1. background to the project

SPRAY IRRIGATION COST BENEFIT STUDY REPORT TO THE ENVIRONMENT AGENCY

J. Morris, E. K. Weatherhead, J. Mills, J. A. L. Dunderdale, T. M. Hess, D. J. G Gowing, C. L. Sanders, J. W. Knox 1999

CONTENTS 1. BACKGROUND TO THE PROJECT ............................................................................................................. 1 1.1 POLICY CONTEXT ................................................................................................................................................ 1 1.2 EXPLORATORY STUDY ........................................................................................................................................ 1 1.3 AIM AND OBJECTIVES ......................................................................................................................................... 1 1.3.1 Aim ................................................................................................................................................. 1 1.3.2 Objectives ....................................................................................................................................... 2 1.4 METHODS AND APPROACH .................................................................................................................................. 2 1.5 REPORT STRUCTURE ........................................................................................................................................... 3 2. DEFINITION OF STUDY TOPIC ................................................................................................................... 5 2.1 IRRIGATION ......................................................................................................................................................... 5 2.1.1 Irrigation scheduling...................................................................................................................... 6 2.1.2 Irrigation benefits .......................................................................................................................... 9 2.1.3 Irrigation costs ............................................................................................................................. 10 2.2 THE CURRENT LICENSING SYSTEM ................................................................................................................... 11 2.2.1 Licence conditions........................................................................................................................ 12 2.2.2 Restrictions on abstraction .......................................................................................................... 13 2.2.3 Exemptions from the need for an abstraction licence .................................................................. 14 2.2.4 Abstraction charges ..................................................................................................................... 14 2.3 NON-AGRICULTURAL AND ENVIRONMENTAL CONSEQUENCES .......................................................................... 16 2.4 SUMMARY ......................................................................................................................................................... 16 3. CASE STUDY AREA ...................................................................................................................................... 17 3.1 THE SOUTH LEVEL ............................................................................................................................................ 17 3.1.2 Hydrological issues ...................................................................................................................... 17 3.2 SOILS................................................................................................................................................................. 18 3.3 CLIMATE ........................................................................................................................................................... 20 3.4 LAND USE ......................................................................................................................................................... 20 3.5 ABSTRACTION LICENCES................................................................................................................................... 20 3.6 EXPERIENCE OF RESTRICTIONS ON IRRIGATION ABSTRACTIONS........................................................................ 21 3.6.1 Restrictions in 1995 ..................................................................................................................... 21 3.6.2 Restrictions in 1996 ..................................................................................................................... 22 3.7 SUMMARY ......................................................................................................................................................... 24 4. FINANCIAL IMPACTS OF RESTRICTIONS ON IRRIGATION ABSTRACTION IN THE SOUTH LEVEL .................................................................................................................................................................. 28 4.1 APPROACH TO BENEFIT ASSESSMENT ............................................................................................................... 28 4.2 MARKET AND PRICES ........................................................................................................................................ 29 4.3 BENEFITS OF YIELD ASSURANCE ....................................................................................................................... 30 4.3.1 Potential crop yields and prices ................................................................................................... 30 4.3.2 Yield response .............................................................................................................................. 30 4.3.3 Irrigation water requirements ...................................................................................................... 33 4.3.4 Benefits of yield assurance ........................................................................................................... 34 4.4 BENEFITS OF QUALITY ASSURANCE .................................................................................................................. 34

4.5 COMBINED YIELD AND QUALITY ASSURANCE BENEFITS .................................................................................. 36 4.6 DISTRIBUTION OF WATER REQUIREMENTS THROUGH THE IRRIGATION SEASON ............................................... 37 4.7 DISTRIBUTION OF IRRIGATION BENEFITS THROUGH THE SEASON...................................................................... 39 4.7.1 Yield assurance benefits ............................................................................................................... 39 4.7.2 Quality assurance benefits ........................................................................................................... 40 4.7.3 Monthly distribution of combined yield and quality assurance benefits ...................................... 40 4.8 IMPACT OF ABSTRACTION RESTRICTIONS ON IRRIGATION PERFORMANCE ....................................................... 42 4.9 ESTIMATION OF FINANCIAL IMPACTS OF IRRIGATION RESTRICTIONS IN SOUTH LEVEL ..................................... 45 4.9.1 Cropping patterns ........................................................................................................................ 45 4.9.2 Estimation of financial impacts due to cessation ......................................................................... 45 4.9.3 Estimation of water use and value ............................................................................................... 46 4.9.4 Incremental financial impact of irrigation restrictions on total licensed quantity ...................... 48 4.9.5 Incremental financial impact of Section 57 restrictions............................................................... 51 4.10 ECONOMIC ANALYSIS OF THE IMPACTS OF IRRIGATION RESTRICTIONS ........................................................... 51 4.11 FARMER COPING STRATEGIES ......................................................................................................................... 52 4.12 CONCLUSIONS AND CAUTIONS ........................................................................................................................ 55 4.12.1 Conclusions ................................................................................................................................ 55 4.12.2 Cautions regarding approach and results ................................................................................. 56 4.13 SUMMARY ....................................................................................................................................................... 56 5. NON-AGRICULTURAL USES OF WATER................................................................................................ 57 5.1 ENVIRONMENTAL RISK ASSESSMENT ................................................................................................................ 57 5.2 APPROACH TO ASSESSMENT.............................................................................................................................. 58 5.2.1 Risk Assessment ............................................................................................................................ 61 5.2.2 Economic Evaluation ................................................................................................................... 62 5.3 ASSESSMENT OF IMPACTS ................................................................................................................................. 63 5.3.1 Industrial abstraction ................................................................................................................... 66 5.3.2 Hydro-power ................................................................................................................................ 67 5.3.3 Commercial fisheries.................................................................................................................... 68 5.3.4 Flood defence ............................................................................................................................... 68 5.3.5 Waste assimilation ....................................................................................................................... 69 5.3.6 Angling ......................................................................................................................................... 70 5.3.7 In-stream recreation..................................................................................................................... 72 5.3.8 Out-of-stream recreation ............................................................................................................. 74 5.3.9 Archaeological Features .............................................................................................................. 75 5.3.10 Aesthetics ................................................................................................................................... 76 5.3.11 Ecology ...................................................................................................................................... 77 5.3.12 Water quality issues ................................................................................................................... 82 5.4 SUMMARY ......................................................................................................................................................... 83 6. POLICY IMPLICATIONS AND RECOMMENDATIONS ........................................................................ 84 6.1 DUTIES AND POLICY .......................................................................................................................................... 84 6.2 POLICY IMPLICATIONS OF COST BENEFIT ASSESSMENT OF RESTRICTIONS ON ABSTRACTORS .......................... 85 6.3 GENERALISED METHOD FOR COST BENEFIT APPRAISAL OF RESTRICTIONS ON ABSTRACTION.......................... 87 6.3.1 Cost:benefit impacts on irrigation ............................................................................................... 87 6.3.2 Environmental impacts................................................................................................................. 88 6.4 RECOMMENDATIONS ......................................................................................................................................... 89 7. REFERENCES ................................................................................................................................................. 91

APPENDIX I

CROP COMMODITY PRICES ............................................................................................ 95

APPENDIX II MARKETING SYSTEMS AND QUALITY BENEFITS OF IRRIGATED PRODUCTS... 99 APPENDIX III

CROP PROFILES ............................................................................................................... 110

APPENDIX IV IRRIGATION WATER REQUIREMENTS ...................................................................... 142 APPENDIX V MODELLED FLOW RESTRICTIONS ............................................................................... 143 APPENDIX VI IRRIGATION AND WATER QUALITY ........................................................................... 144

LIST OF TABLES Table 2.1 Critical moisture sensitive periods ........................................................................................................... 5 Table 2.2 Area of outdoor crops irrigated ............................................................................................................... 6 Table 2.3 Available water capacity and soil type .................................................................................................... 7 Table 2.4 Volume of water applied during the year (tcma) ..................................................................................... 9 Table 2.5 Dry year position assuming adequate water supply ................................................................................ 9 Table 2.6 Summary of average total costs of irrigation ......................................................................................... 11 Table 2.7 Abstraction charges (1996/97)............................................................................................................... 15 Table 2.8 Calculation of annual abstraction charges ............................................................................................ 15 Table 3.1 Soil available water capacities in the study area ................................................................................... 18 Table 3.2 Summary of annual climate data for Mepal........................................................................................... 20 Table 3.3 Cropped areas and % of crop area by soil type, South Level ................................................................ 20 Table 3.4 Random sample of licensed and actual quantities (1995 or 1996) ........................................................ 21 Table 4.1 Example of yield and quality losses associated with withdrawal of irrigation on potato crop, medium AWC soil, design dry year, South Level................................................................................... 29 Table 4.2 Potential yields, price, and net margin, design dry year ....................................................................... 31 Table 4.3 Typical depths of irrigation water applied, design dry year, South Level ............................................. 33 Table 4.4 Benefits of yield assurance due to irrigation by depth applied and soil type, design dry year, South Level ............................................................................................................................................ 35 Table 4.5 Quality assurance price benefits due to irrigation, according to soil AWC .......................................... 36 Table 4.6 Benefits of quality assurance, design dry year....................................................................................... 37 Table 4.7 Combined yield and quality assurance benefits, design dry year, ......................................................... 38 Table 4.8 Typical monthly distribution of irrigation, medium AWC soil, .............................................................. 39 Table 4.9 Estimation of yield and quality assurance benefits of irrigation, medium AWC soil, design dry year, South Level .............................................................................................................. 40 Table 4.10 Monthly distribution of yield and quality assurance benefits due to

irrigation, medium

AWC soil, design year, South Level................................................................................................... 41 Table 4.11 Depth of irrigation (mm/ha) under different design standards and restrictions on licensed

quantities ............................................................................................................................................ 43 Table 4.12 Financial losses associated with restrictions on irrigation of potatoes ............................................... 44 Table 4.13 Impact of restriction on irrigation water availability to meet crop requirements: potato crop; design dry year, South Level, assuming 2.5 mm/day capacity ..................................... 44 Table 4.14 Cropping pattern and distribution of crops by irrigation and soil type for the South Level................ 45 Table 4.15 Financial impacts of cessation at beginning of month for rest of season, medium AWC soil, South Level .......................................................................................................... 46 Table 4.16 Water use and value by month, medium AWC soil, design dry year,

South Level ............................ 47

Table 4.17 Summary of water requirements and benefits of yield and quality assurance, by month, in the South Level .............................................................................................................................. 47 Table 4.18 Whole season water use and benefit assurance, by soil type,

South Level ....................................... 48

Table 4.19 The cost of irrigation restrictions (£/ha on total licensed quantity.…..………….……………………..47 Table 4.20 The cost of irrigation restrictions (£/ha) on unconstrained licensed quantity (20% of total) for typical cropping pattern, South Level, Anglian Region......................................... 51 Table 5.1 Non-agricultural and environmental users/interests ............................................................................. 59 Table 5.2 Summary of methods for assessing the impact of changes in watercourse levels on non-agricultural users and environmental quality ........................................................................ 61 Table 5.3 Assessment of environmental risks associated with reduction with water levels and flows in rivers and watercourses, South Level............................................................................................. 64 Table 5.4 Economic evaluation for South Level .................................................................................................... 65 Table 5.5 Monthly variation in visit patterns as % visiting each month by activity .............................................. 72 Table 5.6 Number of trips per adult per year by activity and region to a river/canal (10 000s) ......................... 75 Table 5.7 Population over 16 by region ................................................................................................................ 75 Table 5.8 The likelihood of significant impacts on each of the interest groups from each of the abstraction scenarios. .............................................................................................................. 80

LIST OF FIGURES Figure 2.1 Example irrigation schedule for maincrop potatoes on a low and medium AWC soil ......................... 8 Figure 3.1 Site location and hydrological information ......................................................................................... 19 Figure 3.2 Ely Ouse Levels 1996 ........................................................................................................................... 25 Figure 4.1 Cost of irrigation restrictions on total licensed quantity ................................................................... 49 Figure 4.2 Cost of irrigation restrictions on unconstrained licensed quantity .................................................... 50 Figure 5.1 Vulnerability of non-agricultural water users and environmental quality to reduced water levels ..... 63 Figure 5.2 A simplified flow chart of trophic levels and provision of habitat structure around a lowland watercourse ........................................................................................................... 78

1.

BACKGROUND TO THE PROJECT

1.1

Policy Context

The Environment Agency is committed to the process of sustainable development which, amongst other things, requires that the need for water for commercial applications is reconciled with those of the natural environment. In pursuit of its powers, the Environment Agency must consider the likely costs and benefits of its policies. This is the case with respect to decisions under Section 57 of the Environment Act 1995, which allow the Agency to impose restrictions on licensed water abstractors in order to protect water resources. In drought conditions, farmers in particular may be required to limit or cease abstraction, with potential consequences for farm production and farm incomes. The Environment Agency has an obligation to identify the likely economic impacts of its cessation orders and set these in general terms against the benefits of the protection and maintenance of water resources and the water environment.

1.2

Exploratory Study

In October 1996 the consultants completed an exploratory investigation of the financial consequences to farmers of the introduction of total bans. This drew on existing knowledge and data regarding crop yield and quality benefits attributable to irrigation, and estimated the lost income due to cessation beginning in each month of the irrigation season. This was done for a range of important irrigated crops. The study produced a simple spreadsheet matrix containing unit rates for estimating income losses and applied these to a hypothetical hydrological unit to show impact at catchment level. The study recommended that further enquiry was justified to improve the reliability of the estimates and suggest a framework for policy formulation. This document reports on this further enquiry and examines the impacts of total bans and partial restrictions.

1.3

Aim and Objectives

1.3.1

Aim

The broad aim of the study is to determine the costs and benefits and implications for sustainable development including conservation impacts, of the imposition of Section 57

1

restrictions on abstractors.

The overall purpose is to help determine appropriate water

resource policies and related implementation guidelines for the Environment Agency which, as far as possible, reconcile agricultural, environmental and other interests during periods of potential water deficit. 1.3.2

Objectives

Specific objectives of the study are: •

to develop a methodology for estimating the costs and benefits to farmers associated with the introduction of restrictions and total bans on irrigation abstraction;

•

to apply this method with respect to a selected hydrological study area, and, in so doing: determine the effects of not imposing restriction or bans on water quality and quantity and the consequences for environmental and other legitimate interests; formulate and evaluate strategies which avoid total bans, such as restrictions or conditions on abstraction; summarise the costs and benefits of proposed restrictions, with particular reference to the consequences for farmers; identify practical ways in which the execution of the Agency's duty with respect to drought restrictions on abstractions can be carried out; and,

•

1.4

drawing on the site specific study, to recommend how the findings can be used to formulate a general framework for policy design.

Methods and Approach

In accordance with the terms of reference, the study objectives were pursued in the context of a selected study area, namely the South Level in the vicinity of Ely, north Cambridgeshire. This was chosen following discussions with the Environment Agency because it contains intensive irrigated agriculture which has been subject to restrictions on abstractions in the recent past. There were two main components of the study. One related to the financial and economic impacts of water restrictions on irrigation for agriculture and the other the impacts of low water levels on other water users and the environment if abstraction was allowed to continue. With respect to the assessment of irrigation economics: Study site specific information was derived mainly from Environment Agency, Ministry of Agriculture, Fisheries and Food (MAFF) and Internal Drainage Board (IDB) sources regarding the hydrological characteristics of the study area, including licensed quantities of water and recent experience of restrictions; and climate, soils, and land use and cropping patterns. 2

A personal interview survey of 20 farmers was carried out to confirm farming and irrigation practices for the major irrigated crops, including information on yields, prices, impacts of and responses to restrictions on irrigation. The consultants used their contacts with the UK Irrigation Association (UKIA). Other information on irrigation practice and likely impacts was obtained from key informant discussions with regional farm management specialists (University of Cambridge), representatives of fresh produce marketing groups and irrigation research specialists in other institutions. Irrigation models developed at Silsoe College were used in support of estimates derived from the farm survey and to predict the likely impact of water restrictions. An Irrigation Water Requirement (IWR) model was used to determine the depths (mm) of water required to meet the evapotranspiration requirements of crops and thereby avoid water stress in the so-called ‘design‘ dry year (the fifth driest year in 20). The model has been used in this study to estimate loss of potential yield if water requirements are not met. A geographical information system (GIS) variant of the model was used to estimate the theoretical volumetric water requirements of the major crops currently irrigated within the study area. The IWR model was also used to test the sensitivity of crops to partial restrictions on irrigation and to limits imposed by the operating capacities of irrigation systems themselves. Information on commodity markets and prices were obtained from official published sources (MAFF Agricultural Market Reports, Potato Marketing Board), trade journals, farmers, marketing agents, and trade associations and retailer organisations. Particular attention was paid to price quality relationships and to commodity prices during dry years. Drawing on the aforementioned data and relationships, a spreadsheet routine was developed to estimate, for the circumstances found within the case study area, the impact of irrigation restrictions in a dry year on crop yield and quality and thereby income to irrigators. With respect to the impacts on non-agricultural water users, a literature review of water and environmental economics was carried out and a simple profile was compiled to summarise the risk and possible economic consequences to other water users of reduced water levels in water courses.

This profile was applied to the study area using data obtained from mainly,

Environment Agency, Local Authority, and Non Government Organisation sources. The findings of the case study were interpreted with respect to the Environment Agency’s policy duties. Recommendations were made on how the methods developed in the case study could be used to provide a generally applicable model for use in other catchments and regions.

1.5

Report Structure

This report summarises the objectives, methods, results and conclusions of the study. Chapter One defines the aims and objectives of the study and the methodology. Chapter Two defines 3

the study topic and issues relating to irrigation. The case study area is described in Chapter Three. The impact of irrigation on yield and quality is discussed in Chapter Four. The impact on environmental and non-agricultural water users of low water levels and flows are discussed in Chapter Five and Chapter Six considers the policy implications and contains recommendations. The report is supported by references and a series of appendices.

Note: The consultants are providing recommendations and the Environment Agency must consider the impact of implementing any such recommendations.

4

2.

DEFINITION OF STUDY TOPIC

This chapter summarises the purpose and practice of irrigation and outlines the benefits and costs. A summary of the current licensing system in England and Wales is presented and the concept of restrictions on abstraction introduced.

2.1

Irrigation

Water is essential for crop growth. When water supply does not meet crop requirements water stress develops in the plant which adversely affects crop growth and yield. The effect of this stress varies according to the crop type, variety and growth period in which the water stress occurs. Two sensitive periods are common to nearly all vegetable plants. First, during establishment at sowing or planting and second, two to three weeks before harvest. Legumes, such as peas, are also sensitive at flowering and pod swell. These moisture sensitive periods are important, for relatively small inputs of irrigation give a high return in terms of yield. Critical moisture sensitive periods for a variety of crops are shown in Table 2.1. Irrigation is used to prevent adverse levels of moisture stress building up in the crop.

Table 2.1

Critical moisture sensitive periods

Crop Apple Beans (Runner) Beetroot Broccoli Brussel sprouts Cabbage Cauliflower Celery Leek Bulb onion Parsnips Potato Strawberries Sugar beet Turnip Source: Bailey, 1990

Critical moisture sensitive growth periods Flowering and fruit set Flowering Root enlargement Head development Sprout formation Head development Head development Continuous Continuous Bulbing and bulb enlargement Root enlargement Stolonisation, tuber initiation and yield formation Fruit development and flower initiation Root enlargement Root expansion

The requirement of the crop for water and therefore, the depths of water applied through irrigation, vary spatially according to soil and agroclimatic factors and temporally, depending on the year to year variation in climate (rainfall and evaporation).

5

The areas of outdoor crops irrigated in the UK in recent years are shown in Table 2.2. The areas irrigated from year to year vary depending on factors such as cropping patterns and climate. Table 2.2

Area of outdoor crops irrigated

Area of outdoor crops irrigated, ha

1987

1990

1992

1995

Total Area Irrigated Potatoes: harvested by 31st July harvested after 31st July Sugar beet Orchard fruit Small fruit Vegetables for human consumption Grass Cereals Other crops grown in the open

76520 5360 29520 10110 1330 2230 11040 6970 7510 7510

164460 8510 43490 27710 3320 3470 25250 15970 28100 8650

107940 8180 45290 10520 2280 2750 20200 7240 7240 4230

156340 8730 53380 26830 2840 3310 27310 10700 13440 8930

Source: MAFF Statistics, 1995 2.1.1

Irrigation scheduling

When the pores in a free-draining soil are filled with water, the soil is temporally saturated and is said to be at ‘field capacity’. In an average summer, a crop sown or planted in such a soil will give a profitable yield with rainfall as the only source of water. In many years, however, the soil is rarely at field capacity throughout the whole growing season and as water is removed from the soil through drainage and by the crop in transpiration, a soil moisture deficit (SMD) builds up in the absence of rainfall. This SMD is expressed as the amount of rainfall or irrigation required (mm) to return the soil to field capacity. If the SMD continues to build up and there is no rainfall, the SMD will reach a critical level (critical SMD) at which point the crop growth is affected. The crop continues to extract water from the soil but at a continually reducing rate until all the available water is used, and in the absence of further rainfall, transpiration ceases and eventually the crop will wilt and die. This available water capacity (AWC) is often used to classify the soil and is an important factor in determining the need for irrigation (Table 2.3). Critical soil moisture deficit levels for irrigated crops are given in the crop profiles in Appendix III. These critical SMDs vary between crops according to their physiology and sensitivity to lower rates of photosynthesis which result under conditions of critical SMD. The SMDs presented in this report are calculated using the ‘old style’ equation and do not take account of evapotranspiration.

6

Table 2.3

Available water capacity and soil type

Available water capacity (AWC) (mm/m)

Soil type

Low (< 100 mm/m) Medium ( (100 - 175 mm/m)

Coarse sand, loamy coarse sand, coarse sandy loam Loamy sand, clay, sandy clay, silty clay, clay loam, sandy loam, loam Silty loam, peaty soils

High (> 175 mm/m) Source: After Knox et al, 1996, Soffe, 1995

The average total irrigation requirements for the crop are well documented (Bailey, 1990, Weatherhead et al, 1994) for a variety of soil types with varying AWCs. These irrigation requirements are used as the basis for creating a strategic irrigation schedule. Some farmers have a set irrigation schedule which they follow each year and which was devised when the irrigation system was designed. The capacity of an irrigation system may be defined as the amount of water which the system is able to supply to the crop within a given period during one application. As a general rule of thumb, irrigation systems are designed to apply the equivalent of 25 mm of rainfall over the whole irrigated area at an interval of 10 days. In designing the irrigation system and schedule, the size and shape of field, soil type, climate, cropping pattern and irrigation equipment available are considered. In the UK, hosereel machines are the commonest irrigator used and the amount of water applied is regulated by the speed of travel of the machine. The system is designed to ensure that the end of a run occurs at a convenient time of day so that the irrigator can be turned around to travel in both directions, up and down the field. With careful management a modern irrigation system can be kept in operation for 20 - 22 hours per day. Farmers generally, make a decision on when to apply irrigation either by applying water when soil moisture deficits rise above a particular level, or, by targeting irrigation during crop sensitive periods. The interval between irrigation applications is usually based on a fixed SMD, the aim of which is to apply water before the crop begins to suffer from moisture stress and before the soil reaches the critical SMD. For example, for maincrop potatoes on a medium AWC soil, the first irrigation is typically applied when the SMD reaches 15 mm. This is usually in late May/early June to aid stolonisation and tuber initiation. Later in the season, the SMD may be allowed to reach 55 mm before water is applied. This process is illustrated in Figure 2.1.

7

Typically, the lighter soils with a lower AWC (eg. coarse sandy loam) require the first irrigation earlier in the season than soils with a medium (eg. loam) or high (eg. peaty) AWC, for given climatic conditions. Subsequent application rates and intervals are determined by crop growth and rate of depletion of soil moisture through transpiration, drainage and evaporation. Volumes of water applied (tcma) on outdoor crops in recent years are shown in Table 2.4. Table 2.5 shows the dry year position assuming adequate water supply, in terms of areas irrigated, water applied and likely depth applied. Figure 2.1

Example irrigation schedule for maincrop potatoes on a low and medium AWC soil Maincrop potatoes 55

Soil moisture deficit

30

(SMD) (mm)

1st application

15

Field capacity Time Medium AWC

Low AWC

8

Table 2.4

Volume of water applied during the year (tcma)

Volume of water applied during the year (Tcma) Total Volume of Water Applied Potatoes: harvested by 31st July harvested after 31st July Sugar beet Orchard fruit Small fruit Vegetables for human consumption Grass Cereals Other crops grown in the open

1987 33630 2350 14700 3430 550 970 4640 3550 2160 1270

1990 133790 6770 51170 20320 2930 3180 18450 13100 11830 6040

1992 75070 5590 38520 4860 1220 2000 12180 4280 2260 4160

1995 162690 9340 74460 21290 2420 4340 25500 9920 5620 10990

Source: MAFF Statistics 1995

Table 2.5

Dry year position assuming adequate water supply

Dry year position assuming adequate water supply

1987

1990

1992

1995

Area of crops likely to be irrigated in a dry year (hectares)

n/a

202620

218550

194000

Volume of water likely to be applied in a dry year (thousand cubic meters)

n/a

179460

233610

244090

Depth of water likely to be applied in a dry year (millimeters)

n/a

90

110

130

Source: MAFF Statistics 1995 2.1.2

Irrigation benefits

Irrigation serves to increase crop yield over and above that obtained through rainfed crop production. This additional yield is determined by crop type and variety, the stage in the crop cycle whenever water is applied, the standard of crop husbandry and environmental factors; especially soil and climate (Morris, 1994). The value added by spray irrigation per unit of water applied is expressed in terms of £ /ha mm. Thus the benefits of irrigation can be expressed in value-added associated with irrigation relative to rainfed cropping. Traditionally, in the UK, potatoes, sugar beet, salad vegetables and soft fruit were irrigated in order to increase crop yields (irrigated areas are shown in Table 2.2). Whilst sugar beet is still sometimes irrigated to increase yields, the emphasis for potatoes, salad crops and soft fruit has switched to quality assurance. Whether producing for the fresh food market or for the food processing industry, farmers are required to supply agreed quantities of high quality, closely specified produce at prescribed delivery times. Irrigation is thus a necessity. It is no longer a low cost, marginal activity to secure yields when rainfall is limited, but is an integral 9

component of an increasingly sophisticated production system (Weatherhead et al, 1996). A water supply failure as a result of irrigation restriction may leave expensive irrigation equipment idle and render totally wasted all the previous inputs into the crop, including irrigation. Reliability of water supplies is now of paramount importance. In addition to the benefits of irrigation for yield and quality, irrigation: • • • • • • • •

enables a wider range of crops to be grown; enables multiple cropping; improves seed bed preparation; cools the soil and atmosphere, thereby making a more favourable environment for growth; provides protection against frost damage; enables effective use of herbicides and fertilisers; softens tillage pans and clods; and, washes out or dilutes salts in the soil.

2.1.3

Irrigation costs

The costs of irrigation vary considerably according to local circumstances, therefore generalisation of costs is difficult (Morris, 1994). Costs vary according to: • • • • •

the crop requirements for irrigation; source of irrigation water (surface or groundwater); the need for water storage; type of application system; and, the size, configuration and topography of the irrigated area, its distance from and height above the water source.

Direct abstraction from surface sources and application by mobile hosereels is the most common irrigation system in the case study area. A summary of average total costs for this main irrigation system is presented in Table 2.6. Capital (initial investment) costs without storage are typically £ 2000 - 3000 /ha (1996 prices). Typically, winter storage increases capital costs by 55 % and by more on less suitable sites. The annual fixed costs (amortisation of capital costs plus insurance), annual variable costs (repairs, fuel, labour and water charges) and the average costs per mm depth of water applied for the selected systems are also shown in Table 2.6. The unit cost of a hosereel system with direct abstraction from a surface source is approximately £ 0.44 per m3 (£ 4.40 per ha mm applied).

10

Water storage increases the average costs per ha mm by an additional 30 % and 70 % for unlined and PVC lined reservoirs respectively, compared to direct abstraction. Average costs for storage based systems are approximately £ 5.7 per ha mm (£ 0.57 per m3 ). Lining of reservoirs increases this to about £ 7.5 per ha mm (£ 0.75 per m3 ), although there may be economies of scale for larger reservoirs. The structure of average costs per unit of water applied is important. Fixed costs account for approximately two thirds of average total costs. Following the initial investment in irrigation equipment, farmers are particularly interested in recovering costs. Variable or running costs are typically £ 1.6 per ha mm for hosereel systems (£ 0.16 per m3 ). Water charges in 1996/97 for unsupported direct summer abstraction for spray irrigation are £ 0.0225 per m3 in the Anglian Region and £ 0.00225 per m3 for winter abstraction. Table 2.6

Summary of average total costs of irrigation

Water Source Direct Abstraction / Storage Application

Surface Direct Hosereel £

%

Borehole Direct Hosereel £

%

Surface Storage (unlined) Hosereel £

Initial Capital Cost £/ha 2530 2970 4320 Annual Costs Fixed Costs * £/ha/yr 350 64 390 68 530 Variable Costs £/ha/yr repairs 94 17 85 15 104 fuel 53 10 57 10 62 labour & machinery 18 3 18 3 18 water 33 6 21 4 3 subtotal £/ha/yr 198 36 181 32 187 Total Costs £/ha/yr 548 100 571 100 717 Total Costs £/ha mm 4.38 4.56 5.74 of which: fixed 2.80 3.12 4.24 variable 1.58 1.44 1.50 Note: Assumes 24 ha irrigated area at 125 mm depth applied/year * Including amortisation of initial capital cost Water costs at 1996 abstraction charges per m3 * depth applied + 20 % contingency

2.2

%

74 15 9 2 175 mm/m, loamy peat). The areas of the South Level under the three AWC soil classes are shown in Table 3.1.

Table 3.1

Soil available water capacities in the study area

Soil type Loamy sand Medium sandy loam Loamy peat Total

Area (ha)

Area (%)

Soil AWC class

1279 56815 23660 81754

1.56 69.49 28.95 100

Low Medium High

18

Figure 3.1

Site location and hydrological information

19

3.3

Climate

The South Level on average receives 536 mm of rainfall per year. The nearest weather station to the case study area is Mepal, near Ely. A summary of the annual data is given in Table 3.2. Table 3.2

Summary of annual climate data for Mepal Rainfall, P (mm)

Potential Evapotranspiration, PETg (mm)

376 667 536

414 587 487

Minimum Maximum Mean

o

o

Note: data for 1973-92, at Mepal, Cambridgeshire (0.18 E 52.48 N)

3.4

Land Use

Table 3.3 shows land use and cropping pattern for the South Level (derived from the MAFF 1994 Agricultural and Horticultural Census). The dominant crops are cereals, sugar beet, potatoes, field vegetables and grass. The percentage area of each crop type found on high, medium and low AWC soils is also shown in Table 3.3.

Table 3.3 Crop category

Cropped areas and % of crop area by soil type, South Level South Level * Area (ha) Area (%)

% area of crop by soil type Low AWC Medium AWC High AWC

Total potatoes 5716 10.1 2 Sugar beet 10899 19.2 2 Orchard fruit 223 0.4 0 Soft fruit 78 0.1 2 Vegetables 5259 9.3 2 Grassland 5237 9.2 2 Cereals 29441 51.8 2 Note: Vegetables refers only to crops grown in the open

3.5

70 70 54 75 63 67 70

28 28 46 23 35 31 28

Abstraction Licences

The licensed quantities of water abstracted for spray irrigation are held by the Environment Agency in their Licensing Data Archive. The licensed quantities for 50 randomly selected abstractors for spray irrigation in the South Level are shown in Table 3.4. Data on actual abstracted volumes for these 50 abstractors are also shown. It is not possible to comment on these data without knowledge of the cropping pattern followed by the licence holder concerned. At the time of writing, information on the total licensed volumes and actual volumes abstracted within the South Level were not available.

20

Table 3.4 No.

Random sample of licensed and actual quantities (1995 or 1996)

1 2 3 4 5 6

Licenced Amount Tcma 3.200 6.500 6.545 10.540 11.364 7.270

7

10.000

9.965

31.00

32

18.181

17.794

55.35

8

6.820

0.005

0.02

33

8.000

5.318

16.54

9 10

70.500 260.000

57.513 256.181

178.90 796.90

34 35

45.500 27.273

45.348 22.533

141.06 70.09

11

31.818

31.817

98.97

36

9.227

3.734

11.62

12

182.000

22.820

70.99

37

54.500

32.468

101.00

13

9.100

6.537

20.33

38

12.500

12.411

38.61

14 15 16

6.800 4.545 12.000

3.151 4.091 9.152

9.80 12.73 28.47

39 40 41

250.000 45.460 80.000

213.092 29.359 43.202

662.86 91.33 134.39

17 18

20.000 27.300

11.520 17.130

35.83 53.29

42 43

68.181 54.500

42.394 54.393

131.87 169.20

19

45.000

15.137

47.09

44

17.840

12.700

39.51

20 21

7.273 9.091

5.899 7.610

18.35 23.67

45 46

195.450 22.730

174.237 16.463

541.99 51.21

22

15.911

15.761

49.03

47

22.730

8.120

25.26

23

68.200

66.595

207.16

48

45.455

24.138

75.09

24 25

13.500 122.700

8.596 120.295

26.74 374.20

49 50

127.291 6.818

41.534 5.152

129.20 16.03

Mean

Licenced amount Actual amount

3.6

Actual Amount Tcma 2.318 6.500 4.942 5.370 6.192 0.007

Actual as % of mean 7.21 20.22 15.37 16.70 19.26 0.02

No. 26 27 28 29 30 31

Licenced Amount Tcma 13.636 58.700 363.636 18.200 50.000 45.500

Actual Amount Tcma 0.930 0.780 25.300 10.152 47.646 23.067

Actual as % of mean 2.89 2.43 78.70 31.58 148.21 71.75

52.59 Tcma 32.15 Tcma

Experience of Restrictions on Irrigation Abstractions

In recent years, the South Level has been subject to a series of restrictions on abstraction for spray irrigation. During 1995 and 1996, voluntary and subsequently formal restrictions under Section 57 of the Water Resources Act 1991, were introduced. Details of events during the period of restrictions are described below.

A time series diagram, Figure 3.2, presents

information on the timing of events, weather conditions and summer retention levels of the Ely Ouse during the period of restrictions in 1996. 3.6.1

Restrictions in 1995

Outflows from the South Level at Denver were high following a wetter than average winter. Monthly rainfall from April 1995 onwards was below average, leading to a rapid fall in surface runoff and very low flows at Denver in July. Flows at Denver dropped below the minimum residual flow (MRF) (114 tcmd) on 1st August 1995 due to exceptionally dry weather in July.

21

Voluntary restrictions were introduced in Mildenhall IDB area on 19 July and on 10/11 August for the remainder of the South Level. A request to restrict abstraction to 12 hours daily between 7 am - 7 pm was made by the National Rivers Authority. On 14 August, levels in the IDB main drain at the Hundred Foot Pumping Station (TL508 890) were below the cessation level of 97.25 mSLD (South Level datum) and irrigators sourced from this watercourse were banned from further abstraction due to cessation clauses in their licences. Four days later, Section 57 of the Water Resources Act 1991 was used to impose a reduction of 50 % of the daily licensed quantity by all South Level surface water spray irrigators, with abstraction restricted to the period between 7 pm and 7 am. Abstractors were advised that if levels continued to fall at Ely, there may be problems with low levels of dissolved oxygen, navigation and salt intrusion through Denver Sluice. On the same day abstractors from the upper reaches of the rivers that feed the South Level system were asked to restrict abstraction to 50% daily rate (night time only). On 23 August, further Section 57 restrictions were imposed and abstraction was limited to 50 % of the daily quantity with abstraction restricted to four nights per week between the hours of 6 pm and 6 am. This also applied to the upper reaches of the rivers that feed the South Level system. In mid September (12th) flow conditions had improved to such an extent that all irrigation restrictions were cancelled. 3.6.2

Restrictions in 1996

In March 1996, in accordance with the MAFF guide ‘Irrigation Good Practice’ a press release was issued, giving warning that the outlook for irrigation was ‘moderate with locally poor irrigation water availability’. By late May, it was clear that water resources were limited with river flows below average and rainfall over the previous 12 months had been less than 70 % of the long term average. A drought liaison meeting was held in May between the Environment Agency, farmers from the South Level and representatives from NFU, CLA, IDB Clerks, Engineers and Chairmen. Everyone was fully briefed on the situation. Requests were made for farmers to voluntarily restrict their abstraction. Inflow into the South Level continued to fall and Section 57 letters were sent to all irrigators in Mildenhall IDB on 20 June, stating that with immediate effect, irrigation should be 22

undertaken at nightime only between the hours of 6 pm to 6 am with abstraction at 50 % of the licensed daily rate. Letters requesting voluntary restrictions by all irrigators sourced from the Soham Lode were issued on 24 June. With immediate effect irrigation should be carried out at night between the hours of 6 pm to 6 am, at 50 % of the daily licensed rate. Section 57 restriction letters were sent to all surface water irrigators in the South Level on 28 June, requiring irrigation to be restricted to 4 nights only (Monday - Thursday) between 6 pm - 6 am at 50 % of the licensed daily rate, with effect from July 1st. These restrictions were necessary in order to protect the river environment and the rights of other users such as navigation, fisheries and recreation. In mid July (10th), following relatively cool and showery weather, Section 57 restrictions were relaxed in the South Level to allow irrigation 7 nights per week at 50 % of the daily rate between 6 pm and 6 am. On the following day restrictions in Mildenhall IDB were also eased from 4 nights out of 7 to 7 nights at 50 % of daily rate. However, further dry weather meant that water levels were below cessation level at Fordham gauging station on the Soham Lode on 18th July so cessation conditions were enforced on irrigators. Also low levels recorded in the South Level on 19th July meant that all South Level irrigators were again restricted to abstracting 4 nights out of 7. On the 23rd July irrigators in the upper reaches of the Ely Ouse were restricted to 7 nights at 50% of daily rate. On 22nd August, Section 57 restrictions were relaxed to 7 nights of the week at 50 % of the daily rate (6pm to 6am) throughout the whole South Level. Following further cooler weather and heavy rainfall, all restrictions were removed on 3rd September, although restrictions for the upper reaches of rivers feeding the South Level remained in force for longer. In summary, restrictions have included: Specific cessation conditions (contained within the licence): abstraction for spray irrigation must cease when the flow of water at point x is less than or equal to x litres/second. 50 % restriction: spray irrigation may only take place between the hours of 6 pm and 6 am with abstraction at 50 % of the daily rate specified in the licence. Time restriction: spray irrigation may only take place on the 4 nights commencing Monday pm, Tuesday pm, Wednesday pm and Thursday pm.

23

In the South Level, since 1992, all new and renewed licences, excluding licences sourced from the Hundred Foot River, are subject to a cessation clause based on flows at the Denver Sluice; the outfall for the South Level.

3.7

Summary

The location of the case study area, hydrological issues, soils, climate and cropped areas have been described in this chapter. The yield and quality benefits of crops grown within this area are presented in the following chapter.

24

Figure 3.2

Ely Ouse Levels 1996

25

Figure 3.2 (continued) Ely Ouse Levels 1996

26

Figure 3.2 (continued) Ely Ouse Levels 1996

27

4.

FINANCIAL

IMPACTS

OF

RESTRICTIONS

ON

IRRIGATION ABSTRACTION IN THE SOUTH LEVEL This chapter considers the benefits of irrigation and the financial impact on farm incomes of imposing restrictions on the abstraction of surface water for irrigation. The chapter develops a methodology for irrigation benefit assessment and applies this to the South Level case.

4.1

Approach to Benefit Assessment

Where rainfall is adequate to meet the water requirements of crops without subjecting them to water stress, providing other husbandry requirements are met, crops will deliver full potential yield and quality. Where rainfall is inadequate, supplementary irrigation can help to reduce the risk of water stress. Thus, the benefits of irrigation are the avoidance of losses in yield and quality associated with water stress. The analysis below adopts this perspective. For irrigated crops two broad possibilities exist: Combined rainfall and irrigation water are sufficient to meet crop water requirements such that stress is not experienced. This implies that the irrigation water applied is sufficient to meet needs. Combined rainfall and irrigation are insufficient to meet crop water requirements and the crop suffers water stress. Irrigation water applied to the crop is insufficient to meet needs because one of the following applies: •

the licensed quantity of water available (either in terms of rate or total volume) is insufficient;

•

irrigation system capacity is insufficient to apply required depths at required intervals;

•

total bans or restrictions have been imposed on irrigators; or

•

cessation clauses contained in the licence have been enforced.

The impact of restrictions on irrigation in any one year depends on the circumstances and outcomes which would occur if they had not been imposed. In very dry periods associated with drought orders, it may be that even in the absence of restrictions by the Environment Agency, licensed water quantities and system capacity would result in water related stress and loss of potential yield and quality. The analysis must consider, therefore, the possibility that for many farmers the ‘without irrigation restriction’ situation is one of less than full potential. 28

Withdrawing irrigation impacts on yield (t/ha) and quality (£/t), with consequences for revenue (£/ha). For example Table 4.1 shows the impact on potato yield, price and revenue for ‘with’ and ‘without’ irrigation on a medium AWC soil in a design dry year.

The

assessment method assumes loss in potential yield valued at the potential price for a quality crop, and a reduction in price reflecting quality loss on the yield actually achieved.

Table 4.1 Yield Price * Revenue

Example of yield and quality losses associated with withdrawal of irrigation on potato crop, medium AWC soil, design dry year, South Level t/ha £/t £/ha

With Irrigation 50 148.8 7440

Without Irrigation 36.4 96.3 3505

Difference due to Irrigation 13.6 52.5 3935 **

Loss of benefit associated with yield loss (£/ha) (13.6 t/ha * £ 148.8 /t) 2024 Loss of benefit associated with quality loss (£/ha) (36.4 t/ha * £ 52.5 /t) 1911 Total loss (£/ha) 3935 ** Note: * prices adjusted for 15 % direct additional costs per tonne. ** before irrigation costs, after irrigation costs (at approx. 170 mm * £1.6 /mm) £3665 (as in Tables 4.9 and 4.10). Figures are subject to rounding for the purpose of presentation.

4.2

Market and Prices

A review was made of agricultural prices pertaining to irrigated crops in England and Wales. Appendix I shows the trends in the average prices of selected crops over recent years. In real terms, agricultural commodity prices have continued to decline. Crops such as potatoes have demonstrated annual price fluctuations reflecting market demand and supply conditions. High prices for potatoes have often been associated with unfavourable climate conditions, especially inadequate rainfall, which have reduced market supply. Annual price fluctuation is highest where a large proportion of the crop is sourced domestically as with potatoes, and where alternative supplies cannot easily be accessed within the season. Many horticultural crops face competition from imports and market conditions are less sensitive to variations in domestic supply. An increase in winter water storage may also reduce price sensitivity to drought. A review was also made of the variation in prices according to quality classifications. These vary considerably between crops, market segments and within and between years (Appendix I). Class 1 and Class 2 differentials are often 20 % to 30 % of Class 1 price. In periods of oversupply, poor quality produce is often rejected completely. In periods of shortage, poor quality produce may still attract normal prices. Of all crops, potatoes have shown the greatest

29

variation in prices in recent years. Deregulation of, and subsequent increase in potato planting in 1995/96 was partly responsible for the recent downturn in prices. The impact of irrigation restrictions on market conditions will vary according to commodity type, the proportion of the national crop affected, whether alternative international sourcing is feasible,

and

the

kind

of

relationships

that

exist

between

producers

and

traders/processors/retailers. There is evidence that supermarkets for example, see benefit in establishing long term, stable contractual arrangements with growers which meet particular market requirements.

Where the quality of a large proportion of the national crop is

threatened, retailers may adjust quality standards accordingly, communicating the reasons to customers. In some cases, however, especially for crops subject to international competition, failure to meet quality standards may lead to commodity rejection or high price discounting.

4.3

Benefits of Yield Assurance

4.3.1

Potential crop yields and prices

Table 4.2 contains estimates of potential yields of crops for the South Level based on farmer interviews and Regional Farm Management Survey results (Murphy 1996, Renwick, 1997), together with estimates of farm gate commodity prices (expressed in 1996/97 constant prices). The latter are based on the top quartile of average annual prices over the last five years reflecting price levels associated with supply shortages in dry years, especially for potatoes. Table 4.2 also indicates the net margin (£/t) after deducting extra direct costs (£/t) per unit of output, such as handling, storage, grading, packing and in some cases transport, which may be saved if output falls. 4.3.2

Yield response

The yield benefit provided by irrigation depends on many factors such as crop type and variety, the growth stage at which irrigation is applied, crop husbandry and environmental factors such as soils and climate. The avoidance of potential yield loss is particularly great on drought prone sandy soils compared to heavier more water retentive soils (Bailey, 1990). Irrigation has particularly encouraged the movement of field scale vegetables and root crops to light soils in order to facilitate timeliness of planting and mechanical harvesting. Estimates of yield benefits attributable to irrigation were derived from farmer interviews and research evidence. Table 4.2. shows the average yield responses of crops to irrigation. These

30

are based on available experimental data and field experience for well managed crops in areas of established irrigation need (ADAS 1977, MAFF 1984). They represent the average returns to water application over the relevant range of water applied, with the latter varying according to soil and climatic conditions. Whereas, crop response to water and hence irrigation is reasonably documented for potatoes, sugar beet, grass and some fruit and vegetables under specific circumstances, for many, especially horticultural crops, reliable data on yield response to irrigation is limited. Table 4.2

Potential yields, price, and net margin, design dry year

31

Crop

Maincrop potatoes Early potatoes Sugar beet Cereals Peas - dried Peas - vining Carrots Parsnips Beetroot Turnips (culinary) Swede (culinary) Celery Leeks Cabbage (spring) Calabrese French beans Runner beans Brussel sprouts Cauliflower Lettuce (outdoor) Bulb onions Salad onions Radish Asparagus Grass-graze Grass-silage Strawberries Raspberries Blackcurrants Rhubarb (in the open) Dessert apples Pears Plums Cherries

Additional costs Combinable crops Sugar beet Potatoes and field scale vegetables Fruit and Horticulture Grass grazed Grass silage

Potential Yields (t/ha)

Crop Price Design Year (£/t)

Extra Crop Costs (£/t)

Extra Net Margin (£/t)

Crop Response (t/ha.mm)

Extra Net Margin less irrig. costs (£/ha.mm)

50 25 42 7 4 5 45 40 40 35 32 25 25 35 8 7 21 13 15 30 40 18 5 3 6 6 8 6 6 35 15 10 8 8

175 200 42 100 130 200 110 200 60 110 110 450 550 160 700 300 520 375 270 460 150 1000 500 500 95 95 1690 2000 650 600 400 450 1400 1000

26.25 30.00 4.20 3.00 3.90 6.00 16.50 30.00 9.00 16.50 16.50 67.50 82.50 24.00 105.00 45.00 78.00 56.25 40.50 115.00 22.50 250.00 125.00 125.00 0.00 20.90 422.50 500.00 162.50 150.00 100.00 112.50 350.00 250.00

148.75 170.00 37.80 97.00 126.10 194.00 93.50 170.00 51.00 93.50 93.50 382.50 467.50 136.00 595.00 255.00 442.00 318.75 229.50 345.00 127.50 750.00 375.00 375.00 95.00 74.10 1267.50 1500.00 487.50 450.00 300.00 337.50 1050.00 750.00

0.08 0.08 0.13 0.02 0.04 0.04 0.13 0.13 0.13 0.13 0.14 0.08 0.08 0.14 0.05 0.06 0.05 0.04 0.07 0.05 0.08 0.08 0.03 0.02 0.03 0.03 0.03 0.03 0.03 0.05 0.02 0.03 0.02 0.02

10.32 12.02 3.33 0.36 2.83 6.18 10.58 20.52 5.05 10.58 11.51 29.02 35.82 17.46 28.17 13.72 20.52 11.17 14.49 15.67 8.62 58.42 9.67 5.92 1.27 0.64 36.45 43.42 13.05 20.92 4.42 8.55 19.42 13.42

% of gross output 3 10 15 25 0 22

Notes: Average response based on ADAS (1977), MAFF (1984). Prices based on upper quartile of 1991 to 1995 year series Extra cost include additional harvesting, handling, drying, and where relevant, direct packaging and marketing costs. Estimates based on Nix (1995), ABC (1996), Outsider's Guide (1995), Renwick (1997) Irrigation costs from Morris et al (1996), charged at £ 1.58 /ha.mm

Table 4.2 expresses yield related benefits in terms of extra value-added (revenue from extra output less costs of extra input). The estimates include allowance for the enforced savings in the marginal costs of the dominant hosereel irrigation system supplied by direct surface abstraction from stream, ditch or river (£ 1.58 /ha.mm, £ 0.16 /m3, 1 ha.mm = 10 m3). These net margins show the average yield related benefit per unit of water applied to the main irrigated crops. For example, on average for the assumptions made, irrigation of maincrop potatoes generates a yield benefit of about £ 10.30 /ha.mm (£ 1.03 /m3) in the design dry year. 32

The yield related benefits per unit of water applied in terms of extra net margin, are highest for soft fruits, followed by horticultural crops, field vegetables and maincrop potatoes. The benefits of irrigation to cereals and grass are relatively low. 4.3.3

Irrigation water requirements

With respect to the South Level, Table 4.3 shows the typical depths of irrigation water applied in order to avoid water stress on the three major soil AWC classes in the design dry year. These estimates were derived from multiple sources, namely farmer interviews, the consultants’ prior knowledge, and from simulation using an irrigation water requirements (IWR) computer model (Hess, 1997). The IWR model used local data on rainfall and evapotranspiration, crop specific irrigation scheduling and agronomic data relating to crop development and rooting characteristics. The model was run using historical daily weather data over a 20 year period (1973 - 1992) from Mepal, Cambridgeshire (0.18 0E, 52.48 0N) which lies within the South Level. The model was run to simulate a daily water balance and to estimate irrigation water requirements for the major crops and for three soil types. The soil types represented the texturally contrasting soils found on the South Level, namely with low (loamy sand), medium (medium sandy loam) and high (loamy peat) available water capacities (AWC). Modelled irrigation applications were based on a strategic irrigation schedule for each crop designed to maintain critical water deficit within acceptable levels. For example, for maincrop potatoes on a medium AWC soil, from June to August, 30 mm of water were applied whenever the soil water deficit reached 55 mm. The ranked annual irrigation needs for all crop categories were probability plotted to determine the 20 % exceedence or ‘design’ irrigation needs.

These are approximately

equivalent to the 5th driest year in 20 typically used in irrigation design. These depths (mm) were compared with farmers’ estimates. For the most part there was a reasonable fit between farmer reported and modelled depths.

Table 4.3

Typical depths of irrigation water applied, design dry year, South Level

33

Crop High AWC Maincrop potatoes Early potatoes Sugar beet Cereals Peas - dried Peas - vining Carrots Parsnips Beetroot Turnips (culinary) Swede (culinary) Celery Leeks Cabbage (spring) Calabrese French beans Runner beans Brussel sprouts Cauliflower

150 45 70 0 70 55 0 75 120 60 60 80 100 60 70 70 90 60 60

Depth (mm) Medium AWC 170 60 105 50 90 60 105 90 140 100 100 100 125 100 110 100 120 100 100

Crop Low AWC 225 80 145 90 105 75 170 150 160 130 130 150 135 135 115 150 140 150

Lettuce (outdoor) Bulb onions Salad onions Radish Asparagus Grass-graze Grass-silage Strawberries Raspberries Blackcurrants Rhubarb (in the open) Dessert apples Pears Plums Cherries

High AWC

Depth (mm) Medium AWC

Low AWC

180 120 100 80 0 50 50 0 0 0 80 75 75 75 75

200 135 125 100 80 70 70 55 50 50 100 100 100 100 100

220 170 160 100 100 90 90 75 70 70 100 125 125 125 125

Note: not all these crops are grown in the South Level

4.3.4

Benefits of yield assurance

Estimates of yield response (t/ha.mm) were combined with data on depths of water applied (mm) in the design dry year to give estimated yield (t/ha) and financial (£/ha) benefits for the major soil types in the South Level (Table 4.4).

4.4

Benefits of Quality Assurance

The benefits of irrigation in terms of quality assurance are substantial and relate to the whole crop, not just to that part of total yield attributable to irrigation.

Quality criteria are

increasingly specified as a condition of contract and sale. Failure to meet quality standards can lead to large price discounting and possibly to rejection. The link between crop quality and irrigation is a complex one. Much of the evidence is anecdotal. A review of research literature, information derived from interviews with farmers and marketing agents operating in the South Level, and analysis of published price data were used to derive estimates of possible price reductions due to poor quality.

Key quality

indicators, such as size or skin quality, were identified and related to market prices. The link between quality indicator, water stress and hence irrigation was explored in an attempt to attribute quality assurance benefits to irrigation.

34

Table 4.4

Benefits of yield assurance due to irrigation by depth applied and soil type, design dry year, South Level

Crop

High AWC Soil

Maincrop potatoes Early potatoes Sugar beet Cereals Peas - dried Peas - vining Carrots Parsnips Beetroot Turnips (culinary) Swede (culinary) Celery Leeks Cabbage (spring) Calabrese French beans Runner beans Brussel sprouts Cauliflower Lettuce (outdoor) Bulb onions Salad onions Radish Asparagus Grass-graze Grass-silage Strawberries Raspberries Blackcurrants Rhubarb (in the open) Dessert apples Pears Plums Cherries Note:

Design Depth (mm)

Yield Benefit (£/t)

Design Year Net Margin Benefit (£/t)

150 45 70 0 70 55 0 75 120 60 60 80 100 60 70 70 90 60 60 180 120 100 80 0 50 50 0 0 0 80 75 75 75 75

12.00 3.60 9.10 0.00 2.45 2.20 0.00 9.75 15.60 7.80 8.40 6.40 8.00 8.40 3.50 4.20 4.50 2.40 4.20 9.00 9.60 8.00 2.40 0.00 1.50 1.50 0.00 0.00 0.00 4.00 1.50 2.25 1.50 1.50

1548 541 233 0 198 340 0 1539 606 635 691 2322 3582 1048 1972 960 1847 670 869 2821 1034 5842 774 0 64 32 0 0 0 1674 332 641 1457 1007

Medium AWC Soil Design Year Design Yield Net Margin Depth Benefit Benefit (mm) (£/t) (£/t) 170 60 105 50 90 60 105 90 140 100 100 100 125 100 110 100 120 100 100 200 135 125 100 80 70 70 55 50 50 100 100 100 100 100

13.60 4.80 13.65 1.00 3.15 2.40 13.65 11.70 18.20 13.00 14.00 8.00 10.00 14.00 5.50 6.00 6.00 4.00 7.00 10.00 10.80 10.00 3.00 1.60 2.10 2.10 1.65 1.50 1.50 5.00 2.00 3.00 2.00 2.00

1754 721 350 18 255 371 1110 1847 707 1058 1151 2902 4478 1746 3099 1372 2462 1117 1449 3134 1164 7303 967 474 89 45 2004 2171 652 2092 442 855 1942 1342

Low AWC Soil Design Depth (mm)

Yield Benefit (£/t)

Design Year Net Margin Benefit (£/t)

225 80 145 90 105 75 170 150 160 130 130 150 135 135 115 150 140 150 220 170 160 100 100 90 90 75 70 70 100 125 125 125 125

18.00 6.40 18.85 1.80 3.68 3.00 22.10 19.50 20.80 16.90 18.20 12.00 18.90 6.75 6.90 7.50 5.60 10.50 11.00 13.60 12.80 3.00 2.00 2.70 2.70 2.25 2.10 2.10 5.00 2.50 3.75 2.50 2.50

2322 962 483 32 298 464 1798 3078 808 1375 1496 5373 2357 3803 1578 3078 1564 2173 3447 1465 9347 967 592 114 58 2733 3039 913 2092 553 1068 2428 1678

Design year, assuming unconstrained application, net of operating costs

In the absence of evidence to the contrary, it was assumed that total irrigation water applications and the total quality benefits due to irrigation are positively and linearly related. Generally, the greater the irrigation need, the greater is the vulnerability of the crop to quality deterioration. In the event of restrictions on irrigation, drought prone soils which require greater depths of irrigation water are likely to produce poorer quality crops than heavier, water retentive soils. Table 4.5 gives the estimates of price reductions due to crops subjected to water stress on the three soil types in the South Level for the design dry year. The bases for the estimates are also shown. Table 4.6 summarises the benefits of quality assurance due to irrigation for the South Level in the design dry year.

35

Table 4.5

Quality assurance price benefits due to irrigation, according to soil AWC

Crop Maincrop potatoes Early potatoes Sugar beet Cereals Peas - dried Peas - vining Carrots Parsnips Beetroot Turnips (culinary) Swede (culinary) Celery Leeks Cabbage (spring) Calabrese French beans Runner beans Brussel sprouts Cauliflower Lettuce (outdoor) Bulb onions Salad onions Radish Asparagus Grass-graze Grass-silage Strawberries Raspberries Blackcurrants Rhubarb (in the open) Dessert apples Pears Plums Cherries

4.5

High AWC 25% 11% 0% 0% 11% 11% 6% 3% 8% 2% 0% 40% 7% 4% 5% 9% 9% 6% 6% 40% 14% 13% 3% 6% 0% 0%

3% 14% 8% 8% 8%

Medium AWC 30% 23% 0% 0% 18% 16% 15% 6% 13% 8% 0% 40% 13% 7% 12% 17% 16% 14% 14% 40% 24% 20% 8% 16% 0% 0% 11% 11% 11% 8% 20% 14% 14% 14%

Low AWC 40% 40% 5% 5% 25% 25% 30% 10% 20% 10% 0% 50% 20% 15% 20% 25% 25% 25% 25% 50% 40% 30% 10% 30% 5% 5% 20% 20% 20% 10% 25% 20% 20% 20%

Dominant indicator scab scab processing quality n/a uniform size & colour uniform size & colour shape, colour & cracks uniform size & shape scab, shape & colour taste n/a blackheart Length, diameter, variability size, head compactness uniformity uniform size & colour uniform size & colour firmness, uniformity discolouration tip burn skin, size uniformity splitting uniformity digestibility digestibility bright, uniformity size, seediness size size, turgidity skin quality, size shape, colour skin, shape splitting

Source Farmer Farmer n/a n/a Literature Literature Trade prices - 30% Farmer Farmer Literature n/a Farmer Farmer Trade prices - 13% Literature Literature Literature Trade prices - 26% Trade prices - 33% Farmer Farmer as bulb onions as parsnips Trade prices - 37% Research Research Trade prices - 34% Trade prices - 22% Trade prices - 22% Trade prices - 22% Trade prices - 35% Trade prices - 25% Trade prices - 25% Trade prices - 25%

Combined Yield and Quality Assurance Benefits

Table 4.7 summarises the whole season combined yield and quality assurance benefits per hectare for selected crops for the design dry year in the South Level. These benefits indicate the loss in value-added borne by farmers if they are not able to apply irrigation water to meet crop requirements. For reasons previously mentioned, farmers may not have the capacity to deliver these requirements, even without restrictions. Table 4.7 also shows the average return (£/m3) to water applied (net of irrigation operating costs).

36

Table 4.6

Benefits of quality assurance, design dry year South Level

Crop

Maincrop potatoes Early potatoes Sugar beet Cereals Peas - dried Peas - vining Carrots Parsnips Beetroot Turnips (culinary) Swede (culinary) Celery Leeks Cabbage (spring) Calabrese French beans Runner beans Brussel sprouts Cauliflower Lettuce (outdoor) Bulb onions Salad onions Radish Asparagus Grass-graze Grass-silage Strawberries Raspberries Blackcurrants Rhubarb (in the open) Dessert apples Pears Plums Cherries

4.6

High AWC

Medium AWC

Low AWC

Quality

Quality

Quality

Loss

Loss

Loss

(£/ha)

(£/ha)

(£/ha)

1663 471 0 22 62 297 182 117 60 0 3348 655 170 158 76 772 239 175 3864 638 1300 39 75 0 0 0 756 279 728 520

1911 929 0 0 20 83 517 340 170 194 0 3091 1073 235 210 51 1248 473 302 3680 1051 1600 80 72 0 0 1180 990 322 1440 1040 441 1176 840

2240 1488 49 26 11 100 756 410 230 199 5625 1430 386 175 8 1755 694 304 4370 1584 1560 100 75 16 16 1944 1560 507 1800 1250 563 1540 1100

Distribution of Water Requirements through the Irrigation Season

A combination of research literature, farmer interviews and computer modelling was used to derive the distribution of irrigation water application during the irrigation season according to 37

crop and soil type in the South Level for the design dry year, assuming applications were not constrained by irrigation system capacity or abstraction restrictions. Table 4.8 shows monthly distributions by crop for medium AWC soils in the design dry year. In dry conditions, irrigation schedules are usually earlier than otherwise.

Appendix IV contains details of

monthly irrigation schedules by crop and soil type.

Table 4.7

Combined yield and quality assurance benefits, design dry year, South Level

Crop

Maincrop potatoes Early potatoes Sugar beet Cereals Peas - dried Peas - vining Carrots Parsnips Beetroot Turnips (culinary) Swede (culinary) Celery Leeks Cabbage (spring) Calabrese French beans Runner beans Brussel sprouts Cauliflower Lettuce (outdoor) Bulb onions Salad onions Radish Asparagus Grass-graze Grass-silage Strawberries Raspberries Blackcurrants Rhubarb (in the open) Dessert apples Pears Plums Cherries

Total Irrigation Benefits High Medium

Low

Total Irrigation Benefits High Medium

Low

AWC soil

AWC soil

AWC soil

AWC soil

AWC soil

AWC soil

(£/ha)

(£/ha)

(£/ha)

(£/m3 )

(£/m3 )

(£/m3 )

3211 1012 233 0 221 402 0 1721 723 694 691 5670 4237 1218 2129 1036 2619 909 1044 6685 1673 7142 813 0 64 32 0 0 0 2232 1163 920 2185 1527

3665 1650 350 18 275 454 1628 2186 877 1251 1151 5993 5550 1981 3309 1423 3710 1590 1751 6814 2215 8903 1047 546 45 45 3185 3161 974 3532 1482 1296 3118 2182

4562 2450 532 110 308 564 2553 3488 1038 1574 1496

2.1 2.2 0.3

2.2 2.8 0.3

0.3 0.7

0.3 0.8 1.6 2.4 0.6 1.3 1.2 6.0 4.4 2.0 3.0 1.4 3.1 1.6 1.8 3.4 1.6 7.1 1.0 0.7 0.1 0.1 5.8 6.3 1.9 3.5 1.5 1.3 3.1 2.2

2.0 3.1 0.4 0.1 0.3 0.8 1.5 2.3 0.6 1.2 1.2

6803 2744 3978 1585 1585 2258 7817 3049 10907 1067 667 130 74 4677 4599 1420 3892 1803 1631 3968 2778

2.3 0.6 1.2 1.2 7.1 4.2 2.0 3.0 1.5 2.9 1.5 1.7 3.7 1.4 7.1 1.0 0.1 0.1

2.8 1.6 1.2 2.9 2.0

4.5 2.0 2.9 1.4 1.1 1.6 3.6 1.8 6.8 1.1 0.7 0.1 0.1 6.2 6.6 2.0 3.9 1.4 1.3 3.2 2.2

38

Table 4.8

Typical monthly distribution of irrigation, medium AWC soil, design dry year, South Level

Crop

April

Maincrop potatoes Early potatoes Sugar beet Cereals Peas - dried Peas - vining Carrots Parsnips Beetroot Turnips (culinary) Swede (culinary) Celery Leeks Cabbage (spring) Calabrese French beans Runner beans Brussel sprouts Cauliflower Lettuce (outdoor) Bulb onions Salad onions Radish Asparagus Grass-graze Grass-silage Strawberries Raspberries Blackcurrants Rhubarb (in the open) Dessert apples Pears Plums Cherries

0 15 0 0 0 0 0 0 0 10 0 10 0 0 0 0 0 0 0 10 10 10 10 10 5 30 0 0 0 5 0 0 0 0

Monthly Distribution of Irrigation (%) May June July August September 15 80 0 0 20 20 30 25 10 30 25 20 20 20 20 20 20 20 10 15 20 20 20 20 25 40 25 10 0 30 10 25 0 0

30 5 40 0 40 25 30 35 30 30 25 25 25 25 25 25 25 40 20 20 30 30 20 25 35 30 35 25 40 30 20 25 15 15

30 0 40 70 40 30 35 30 35 30 25 30 30 30 25 30 30 40 30 25 30 30 20 25 30 0 35 25 25 30 25 25 25 30

25 0 20 30 0 20 5 10 25 0 25 15 15 25 30 25 20 0 35 20 10 10 20 20 5 0 5 25 20 5 25 25 50 40

0 0 0 0 0 5 0 0 0 0 0 0 10 0 0 0 5 0 5 10 0 0 10 0 0 0 0 15 15 0 20 0 10 15

4.7

Distribution of Irrigation Benefits through the Season

4.7.1

Yield assurance benefits

Total 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100

The percentage distribution of total irrigation water applied in any one month was used to estimate the monthly distribution of yield assurance benefits within the irrigation season. The example of maincrop potatoes on a medium AWC soil is shown in Table 4.9, part (a). The critical periods were identified when crops are most vulnerable to water stress (Appendix IV) and when withholding water might have most impact on saleable yield.

39

International research, mainly in situations where irrigation provides the major part of crop water requirements, suggests that water has a varying physiological effect according to the crop’s stage of development (FAO 1977). Weighting factors can be used to reflect this, for example by giving relatively more weight to water applied at the time of tuber initiation on potatoes compared to the later vegetative stage. However, in the UK under conditions of supplementary irrigation, there is insufficient information to construct reliable weightings and it was felt that the relative distribution of water within the season already reflected the relative impact on yield. Furthermore, sensitivity analysis showed that weighting had limited effect on the over all monthly distribution of yield benefits.

For these reasons, yield response

weightings were not used at this stage of the enquiry.

Table 4.9

Estimation of yield and quality assurance benefits of irrigation, medium AWC soil, design dry year, South Level

Irrigation water requirement (mm) Potential yield (t/ha) Unirrigated yield (t/ha) Yield Benefit (£/ha) Quality Price Reduction (%) Quality Benefit (£/ha)

170 50 36 1754 30% 1911 April

May

June

July

% of total mm

0 0

15 26

30 51

30 51

25 43

0 0

100 170

% of total % of total £/ha

0 100 1754

15 100 1754

30 85 1491

30 55 965

25 25 439

0 0 0

100

(b) Quality benefit Quality loss on cessation * Quality Losses on cessation *

% of total % of total £/ha

0 100 1911

10 100 1911

50 90 1720

30 40 764

10 10 191

0 0 0

(c) Total Loss on Cessation * Losses per m3 saved

£/ha £/m3

3665 2.16

3665 2.16

3211 2.22

1729 1.85

630 1.48

0 0

(a) Irrigation water requirement Irrigation water requirement Yield Benefit Yield loss on cessation * Yield Losses on cessation *

August September

Total

1754

100 1911 3665

* Cessation asssumed to occur at start of month

4.7.2

Quality assurance benefits

In a similar way, research evidence and farmer views were used to apportion the total quality assurance benefits to particular months of the irrigation season.

This reflected the

vulnerability of crops to water stress as it affected key quality indicators such as scab in potatoes, or skin blemish or size in onions. In this respect, quality benefits were not linearly related to irrigation applications in each month. The total quality assurance benefit was distributed amongst the months of the irrigation season accordingly (Table 4.9, part (b)). 4.7.3

Monthly distribution of combined yield and quality assurance benefits 40

Monthly yield and quality assurance benefits were aggregated for each month for each crop/soil type combination for the design dry year. The cumulative benefit was identified for each month, and conversely the benefits foregone if irrigation was stopped completely in any one month for the rest of the season. Table 4.9 part (c) shows this for potatoes on medium AWC soils (design dry year, South Level). Table 4.10 summarises the financial losses (net of savings in irrigation costs) of cessation for a range of crops on medium soils in the design year for the South Level.

Table 4.10

Monthly distribution of yield and quality assurance benefits due to irrigation, medium AWC soil, design year, South Level

Crop Maincrop potatoes Early potatoes Sugar beet Cereals Peas - dried Peas - vining Carrots Parsnips Beetroot Turnips (culinary) Swede (culinary) Celery Leeks Cabbage (spring) Calabrese French beans Runner beans Brussel sprouts Cauliflower Lettuce (outdoor) Bulb onions Salad onions Radish Asparagus Grass-graze Grass-silage Strawberries Raspberries Blackcurrants Rhubarb (in the open) Dessert apples Pears Plums Cherries

April £/ha 3665 1650 350 18 275 454 1628 2186 877 1251 1151 5993 5550 1981 3309 1423 3710 1590 1751 6814 2215 8903 1047 546 45 45 3185 3161 974 3532 1482 1296 3118 2182

May £/ha 3665 1449 350 18 275 454 1628 2186 877 1145 1151 5702 5443 1981 3309 1423 3710 1590 1751 6501 1993 8012 950 491 43 32 3185 3161 974 3427 1482 1296 3118 2182

June £/ha 3211 129 350 18 224 380 1191 1725 755 731 863 5122 4333 1608 2626 1144 3093 1366 1515 6031 1708 6392 741 375 32 14 2448 2746 974 2368 1334 994 2883 2182

July £/ha 1729 0 210 18 114 254 755 1010 458 317 576 4397 2892 1148 1767 785 2103 683 1105 5404 1306 3881 524 220 16 0 1274 2005 649 1020 1037 604 2121 1813

August £/ha 630 0 70 5 0 93 159 321 177 0 288 3526 1227 531 930 353 865 0 579 4620 432 1050 306 95 2 0 218 1066 357 105 615 258 1283 1074

September £/ha 0 0 0 0 0 19 0 0 0 0 0 0 448 0 0 0 123 0 72 3993 0 0 97 0 0 0 0 326 130 0 192 0 194 285

Total £/ha 3665 1650 350 18 275 454 1628 2186 877 1251 1151 5993 5550 1981 3309 1423 3710 1590 1751 6814 2215 8903 1047 546 45 45 3185 3161 974 3532 1482 1296 3118 2182

41

4.8

Impact of Abstraction Restrictions on Irrigation Performance

It was earlier recognised that constraints may occur because licensed quantities are insufficient, systems capacity may be inadequate to meet peak demands, licence cessation clauses are enforced or restrictions are imposed by the Environment Agency, or water supply simply runs out. The impact of restrictions on irrigation were examined using the IWR model applied to the major irrigated crop, potatoes, which in the South Level account for 49 % and 62 % of the irrigated area and water use respectively (Appendix V). Table 4.3 shows the estimated annual water requirements for potatoes on the three groupings of soil AWC in the South Level based on estimates derived for the period 1973 to 1992, confirming the year to year variation in unconstrained irrigation. In 5 years out of 20, water requirements exceed 170 mm (20 % exceedence) on medium AWC soils. In recent years, there has been a trend to design system capacity accordingly, capable of delivering 5 mm/day for potatoes. Previously, however, the standard design was 2.5 mm/day and many licences reflect this. Table 4.11 shows that this would limit seasonal delivery to 149 mm, a 12 % reduction imposed by system constraints. In practice it is likely that farmers could accommodate this limit by careful scheduling, especially if crops with different schedules are being irrigated. The imposition of formal restrictions on abstraction rates can, however, have considerable impact on ability to meet water requirements. A restriction on abstraction rate and/or hours of operation which reduces capacity to 1.2 mm/day or 0.6 mm/day would reduce design dry year delivery to 99 mm or 68 mm respectively, ie. a 40 % and 60 % reduction respectively. The extent to which restrictions impose real constraints on capacity are difficult to generalise. Much depends on particular farm circumstances regarding licence conditions (specified hourly, daily and seasonal abstraction limits), irrigation system characteristics and the irrigation schedules of the crops irrigated. For example, some farmers may find that they can accept reductions in licensed abstraction rates (m3/hour or m3/day) without compromising their total system capacity. This was the case with many farmers in the South Level where system capacity imposes greater restrictions on abstraction rates than licence conditions. In contrast, the imposition of restrictions which confine irrigation to particular days (e.g. only 4 out of 7) does place pressure on the scheduling and operation of the irrigation system such that 42

there is an increased risk that crops are exposed to water stress. The greater the restrictions on abstractions, the greater are the likely impacts. Table 4.11

Depth of irrigation (mm/ha) under different design standards and restrictions on licensed quantities

Flow Rate Year 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 20% Exceedence IWR mean stdev

Unlimited Potato Design Standard Design 50% restr. 25% restr. (10 mm/day) (5 mm/day) (2.5 mm/day) 1.2 mm/day 0.6 mm/day 72 54 192 264 96 12 72 72 90 54 180 138 72 90 54 66 228 216 114 108

72 54 192 264 96 12 72 72 90 54 180 138 72 90 54 66 228 216 114 108

72 54 192 204 84 12 72 60 90 54 150 138 72 90 54 66 198 174 114 96

72 54 102 114 72 12 72 36 90 54 90 96 72 90 54 54 126 102 72 84

42 54 72 72 42 12 42 24 60 42 60 54 42 60 54 42 84 72 42 84

170

170

149

99

68

112 68

112 68

102 55

76 27

53 19

Table 4.12 shows the financial impacts of the restrictions described in Table 4.11. For the assumptions made, whole season cessation of irrigation on potatoes on medium AWC soils would result in a £ 3665 /ha loss of potential net income, whereas a 50 % restriction would result in a loss of £ 1540 /ha. A 75 % restriction on licensed quantities results in a financial loss equivalent to about 60 % of that which would be incurred as a consequence of a total ban for the whole season. Generally, for every 10 % restriction in water application imposed by limited abstraction rate or system capacity, there is approximately an 8 % loss in potential net income from irrigation. The estimates of the impact of partial restrictions are likely to overestimate actual loss because farmers can adopt strategies to minimise loss by rescheduling to reduce peak demands and to make the most of water available.

43

Table 4.12 Potato Design 5 mm/day

Financial losses associated with restrictions on irrigation of potatoes

Income Loss Compared to Design Appl. £/ha High AWC soil 150 3210 Medium AWC soil 170 3665 Low AWC soil 225 4370 Index of income loss 100

Standard design 2.5 mm/day

Income Loss Compared to Design Appl. £/ha

50% Restriction 1.2 mm/day

Income Loss Compared to Design Appl. £/ha

75% Restriction 0.6 mm/day

Income Loss Compared to Design Appl. £/ha

141

2990

56

1220

149

3230

71

1540

102

2200

208

4020

93

1790

149

2880

91

86

1830

40

60

The IWR model was also used to assess impact of partial restrictions imposed at different times in the irrigation season. Table 4.13 shows, for example, that a 50 % restriction on abstraction in June for the rest of the season would reduce water available for irrigation from 170 mm to 103 mm, a 40 % reduction. For the assumptions made, the percentage reductions in water applied are indicative of the percentage reduction in net income. A 50 % restriction beginning June will result in a 40 % loss of the potential benefit of irrigation, or conversely, 60 % of potential benefits will be obtained. In practice, June is a very sensitive time for potatoes. Losses could be greater due to scab attack. But there again, growers may limit scab risk by irrigating more than usual in May to increase soil moisture. Prior knowledge of restrictions would encourage this practice. Table 4.13

Impact of restriction on irrigation water availability to meet crop requirements: potato crop; design dry year, South Level, assuming 2.5 mm/day capacity High AWC

Unrestricted Requirement Restrictions on abstraction rates beginning 50% July 50% June followed by 75% July 50% in June, relaxed in August

mm 150

% 100

Medium AWC mm % 170 100

100 74 124

67 50 83

103 80 123

61 47 72

Low AWC mm 225

% 100

170 118 165

76 53 73

These estimates indicate the effect of Section 57 restrictions on licences which are otherwise not subject to cessation clauses.

44

4.9

Estimation of Financial Impacts of Irrigation Restrictions in South Level

4.9.1

Cropping patterns

Table 4.14 contains estimates of cropping pattern for the South Level area, based on MAFF relevant parish statistics derived from the Annual Agricultural Census. The latter uses broad categories of crops which have been converted into crop types using information derived from the survey of farms in the study area. The proportion of crops which are irrigated was estimated from MAFF’s periodic irrigation survey results made available at County level, modified to reflect South Level conditions on the basis of farmer and IDB information. It is estimated that about 19 % of the total South Level area is irrigated in a dry year, compared to an all Cambridgeshire estimate of about 9 %. An existing GIS database developed at Silsoe (Knox et al, 1997) was used to combine information on cropping pattern with soil type data to determine cropping pattern by soil AWC type. Low AWC soils account for less than 2% of all soils. Irrigation has been associated with the adoption of arable farming on these soils. For this reason, it was assumed that all crops on these soils would receive irrigation in very dry years. It was assumed that the remaining proportion of the irrigated area for each crop was distributed between medium and high AWC soils in the proportions shown in Table 4.14. Table 4.14

Cropping pattern and distribution of crops by irrigation and soil type for the South Level

Total area (ha)

Potatoes

53323

maincrop early total

Sugar beet

Area (ha) 5518 600 6118 10601

total Cereal

26118

Grassland Vegetables

Salad crops

Soft fruit Orchard fruit

4.9.2

848

2

70

28

3

784

2

70

28

1

51

1

68

31

80 70 50 75 60 73 100 100

1440 1455 98 200 115

2 2 2 2 2 2 2 2

63 63 63 63 63 63 63 63

35 35 35 35 35 35 35 35

26 26 0 0 19

6 0 0 0 10114

2

75

23

0

54

46

26118 5107

total onions carrots and other roots brassica (using calabrese as indicator) other (using leeks as indicator) peas / beans (using French beans as indicator) total lettuce celery total strawberries total apples total

8 10601

total

Grand total

% of croprigated area Crop by soil type (%) irrigated (ha) Low AWC Medium AWC High AWC 70 3863 2 70 28 85 510 0 70 30

5107 1800 2078 195 267 191 4531 500 246

500 246

746 22 22 80 53323

80 53323

Estimation of financial impacts due to cessation

The financial impacts per hectare of stopping irrigation at the beginning of a specified month for the remainder of the season were identified for each crop for each soil type and aggregated 45

according to the cropping pattern previously defined for each soil type. Table 4.15 presents the information for Medium AWC Soils. Data for other soils is given in Appendix IV. Table 4.15 shows that, in the design dry year, stopping irrigation in April for the rest of the season results in a loss of potential yield and quality benefits on 6220 ha of irrigated medium soils of £18.1 million. Table 4.15

Financial impacts of cessation at beginning of month for rest of season, medium AWC soil, South Level

£000 Potatoes

Sugar beet Cereal Grassland Vegetables

Salad crops

Soft fruit Orchard fruit

maincrop early total total total total onions carrots and other roots brassica (using calabrese as indicator) other (using leeks as indicator) peas / beans (using French beans as indicator) total lettuce celery total strawberries total apples total

Grand total

4.9.3

Area (ha) 2680 357

April £000 9824 589

May £000 9824 517

June £000 8606 46

July £000 4635 0

August £000 1688 0

September £000 0 0

Total £000 9824 589

454 187 0 903 908 60 125 71

159 3 0 1999 1479 199 695 101

159 3 0 1799 1479 199 682 101

159 3 0 1542 1082 158 543 81

95 3 0 1179 685 106 362 56

32 1 0 390 144 56 154 25

0 0 0 0 0 0 56 0

159 3 0 1999 1479 199 695 101

315 155

2146 929

2048 884

1900 794

1702 681

1455 546

1258 0

2146 929

4

13

13

10

5

1

0

13

0

0

0

0

0

0

0

0

6220

18137

17708

14924

9511

4492

1314

18137

Estimation of water use and value

The quantities of irrigation water used in each month of the design dry year were estimated for the South Level, based on estimated depths of water per ha of crop for specified soil types and the relevant irrigated areas. For example, Table 4.16 shows the quantities of water used by crop on medium AWC soils in the design dry year, and hence the amount of water potentially saved in the event of ceasing (and not re-commencing) irrigation at a particular point in the season. The table shows that crop water requirements peak at about 2.5 million m3 per month in June and July. A total water use of 8.5 million m3 over the season delivers a potential benefit of £ 18.1 million, equivalent to an average benefit of just over £ 2 /m3. Average depth is approximately 1400 m3 per ha (140 mm/ha) and average benefits are approximately £ 2920 per ha. The table also indicates the average marginal value (£/m3) of supplying water for the rest of the season and for a specific month. These estimates are based on net crop water requirement.

Estimates of abstraction water requirement and benefits per m3 should be

adjusted up or down about 15 % respectively to reflect system and other delivery losses.

46

Table 4.16

Water use and value by month, medium AWC soil, design dry year, South Level

Water use, medium AWC soil, by month

Area (ha) 2680 357

April 000m3 0 32

May 000m3 683 171

June 000m3 1367 11

July 000m3 1367 0

August 000m3 1139 0

September 000m3 0 0

Total 000m3 4556 214

Potatoes

maincrop early

Sugar beet Cereal Grassland Vegetables

total total total onions carrots and other roots brassica (using calabrese as indicator) other (using leeks as indicator) peas / beans (using French beans as indicator)

454 187 0 903 908 60 125 71

0 0

0 0

191 0

191 65

95 28

0 0

477 93

122 0 0 0 0

244 286 13 31 14

366 286 17 39 18

366 334 17 47 21

122 48 20 23 18

0 0 0 16 0

1218 954 66 157 43

Salad crops

lettuce celery

315 155

63 15

95 31

126 39

158 46

126 23

63 0

630 155

Soft fruit

strawberries

4

0

1

1

1

0

0

2

Orchard fruit

apples

0

0

0

0

0

0

0

0

232 8594 18137 2.11 1.84

1569 8362 17708 2.12 1.77

2459 6792 14924 2.20 2.20

2612 4333 9511 2.20 1.92

1643 1721 4492 2.61 1.93

79 79 1314 16.70 16.70

8594

Total (ha) Water use per month 000m3 Cumulative water use 000m3 Benefit per month £000 Average value of water over remaining season £/m3 Marginal value of water per month Average depth m3/ha Average benefit £/ha Average benefit £/m3

6220

1382 2916 2.11

Table 4.17 summarises the estimates of water requirements and the benefits of yield and quality assurance for each month in the irrigation season for the South Level as a whole. June and July are the peak months of water use and benefit. Total water use is estimated to be 12.7 million m3 in a dry year (adjusted to 14.6 million m3 to allow for losses of about +15%). At the time of writing, the total licensed quantities issued in the South Level had not been confirmed. Table 4.17 shows the loss of income to farmers if irrigation is stopped at the beginning of a given month and not recommenced, and the volume of water saved by doing so.

Table 4.17

Summary of water requirements and benefits of yield and quality assurance, by month, in the South Level April

May

June

July

August

Water use per month

000m3

339

2302

3654

3929

2404

September 120

Cumulative water use

000m3

339

2641

6295

10224

12628

12748

Benefit per month

£'000

602

3866

7477

7068

4588

2115

Average value of water per month

£/m3

1.78

1.68

2.05

1.80

1.91

17.60 *

Total benefit loss with cessation beginning in month

£'000

25716

25114

21247

13770

6703

2115

Water saving with cessation beginning in month

000m3

12748

12410

10107

6453

2524

120

Average value of water over remaining part of season

£/m3

2.02

2.02

2.10

2.13

2.66

17.60

*reflects high returns on end of season horticultural and salad crops

47

Table 4.18 summarises relevant statistics on whole season water use and benefit assurance by soil type and for the South Level as a whole. Average depth applied is 1260 m3/ha, and average benefit is £ 2.02 /m3 before water loss adjustment. The average returns to irrigation water are lower on the low AWC soils because of the tendency to irrigate relatively less valuable crops in dry years such as sugar beet, cereals and some grass compared to the much higher value cropping on other soil types.

Table 4.18

Whole season water use and benefit assurance, by soil type, South Level Total

High

Medium

Low

All Soils

AWC

AWC

AWC

Water used, 000m3

12748

2910

8594

1244

Benefit, £000

25714

6544

18137

1032

Irrigated area, ha

10114

2892

6220

1002

Average depth, m3/ha

1260

1006

1382

1241

Average benefit, £/ha

2542

2263

2916

1030

Average benefit, £/m3

2.02

2.25

2.11

0.83

The overall average value of water for the South Level in the design dry year is about £ 2 /m3. This is considerably higher, by a factor of at least 2, than the average returns to irrigation over a number of years, reflecting the high prices and high incremental benefits attributable to water in dry years. The above estimates must be interpreted with caution. For the most part, they are based on secondary data sources (especially regarding cropping patterns and proportions of crops irrigated) and best available information on crop yield and quality response. A critique of the method for benefit assessment is presented in Section 4.12. 4.9.4

Incremental financial impact of irrigation restrictions on total licensed quantity

Figure 4.1 and Table 4.19 demonstrate the effect of introducing restrictions on total licensed quantity at different times of year for the South Level. 100% restriction implies a total ban. A 75% restriction reflects a 75% reduction on the licensed rate of abstraction and a financial loss equivalent to 60% of the whole season cessation loss. 50% and 10% restrictions result in financial losses of 40% and 8% respectively. 48

Figure 4.1 Cost of irrigation restrictions on total licensed quantity

49

Figure 4.2 Cost of irrigation restrictions on unconstrained licensed quantity

50

Table 4.19 The cost of irrigation restrictions (£/ha) on total licensed quantity for typical cropping pattern, South Level, Anglian Region % restricted April May

June

July

August

September

10

203

199

167

106

51

14

50

1,017

996

834

529

254

71

75

1,525

1,495

1,251

793

381

107

100

2,542

2,491

2,084

1,322

636

178

4.9.5

Incremental financial impact of Section 57 restrictions

Figure 4.2 and Table 4.20 demonstrate the incremental financial impact of restriction to irrigation at different times of the year for licences which are not subject to cessation clauses. For the Hundred Foot catchment within the South Level, approximately 20% of spray irrigation licensed quantities are unconstrained. The remaining 80% of the licensed quantities are subject to a cessation clause which comes into affect when water levels/flows drop below a specified limit. It is assumed that Section 57 restrictions would apply simultaneously to the introduction of cessation clauses specified in licences. Table 4.20 The cost of irrigation restrictions (£/ha) on unconstrained licensed quantity (20% of total) for typical cropping pattern, South Level, Anglian Region. % restricted

April

May

June

July

August

September

10

41

40

33

21

10

3

50

203

199

167

106

51

14

75

305

299

250

159

76

21

100

508

498

417

264

127

36

4.10 Economic Analysis of the Impacts of Irrigation Restrictions The preceding analysis adopted a financial perspective whereby yield and quality losses, net of savings in expenditure, were valued at the market prices paid and received by farmers. The analysis thus shows the effect of irrigation restrictions on farmer income and is consistent with the Environment Agency’s duty to consider the impact of its policies on individuals, businesses and organisations (see Section 6.1). For the purpose of cost benefit analysis, the Environment Agency is also required to adopt a broader economic assessment whereby policies or actions are judged in terms of their impact on the efficiency of resource use and the achievement of social welfare objectives. Amongst

51

other things, this requires adjusting financial prices to economic values to reflect the real value of resources used and outputs produced. This adjustment is particularly difficult in agriculture because of the complexity of direct (such as commodity price support) and indirect (trade protection) measures. Two relatively straightforward (but not necessarily reliable) measures of adjustment involve removing relevant taxes and subsidies, and or expressing commodities values at international rather than protected internal market prices. MAFF recognise the importance of adjusting financial to economic prices to obtain a better estimate of economic value-added to the national economy. In the flood defence sector, MAFF advise the use of adjustment factors to net out the costs of support and subvention for commodities which are heavily supported and or regulated. With respect to the impacts on the economic value-added from irrigation, however, it is argued that the preceding financial analysis can be used as a reasonable indicator of the short term economic impact, without the need for further adjustment, because: • the commodities affected are mainly non-regulated produce (now including potatoes) operating in a relatively free market where prices reflect willingness to pay and benefit derived in consumption; • the significant rise in prices during supply deficit periods is indicative of the value of consumption of these commodities, (and the relatively high consumer surplus enjoyed during years of normal supply); • shortfalls in irrigated produce are partly substituted by imports which involve foreign exchange costs and balance of payment impacts. The same applies to lost exports; and, • the loss of output from irrigation reduces activity levels in local agri-business and food industry sectors which are major employers and income generators in predominantly agriculturally dependent communities. If it appears, however, that restrictions on abstraction are likely to become more frequent, a more detailed strategic review of the economic performance of the irrigation sector will be justified.

4.11 Farmer Coping Strategies Farmers in the South Level are cognisant of the value of water for irrigation and the vulnerability of high value cropping to water stress, whether too much or too little. Drainage to remove excess and irrigation to supplement rainfall are key elements of farming systems on the South Level.

52

The economic importance of irrigation is confirmed by the preceding analysis. The analysis shows that the costs of complete cessation are potentially very high. Most farmers would draw benefit from partial restrictions introduced early such that the risk of complete cessation is reduced. It is important therefore that farmers are informed of the likelihood of restrictions as early as possible and that they can be party to their introduction, if possible under voluntary arrangements. Prior knowledge of partial restrictions will allow farmers to apply coping strategies which suit their particular circumstances. In the short term (within the season of restriction) these might include: •

rescheduling the timing of water abstraction, possibly beginning earlier (to reduce soil water deficit) or later to save total licensed quantities;

•

rescheduling allocation of water amongst crops;

•

modifying depths applied and/or irrigation intervals; and,

•

the retention of high levels in farm and arterial drainage systems.

The viability of these options depend on licence conditions, soil water characteristics, cropping practices, crop market requirements and the degree of flexibility afforded by irrigation systems. Coping strategies also reflect personal attitude to risk. Observations in April 1997 in the South Level confirm earlier applications than normal in response to dry conditions. The IDBs have retained higher than normal levels in the ditch system in order to maintain soil water levels. This technique of sub irrigation is important for all cropped areas, whether surface irrigated or not. (Indeed a reduction of levels in the drainage system in the summer period could compromise the un-irrigated farming, which is the majority of the area). Where water is limited, farmers have a choice whether to reduce application depths over the intended crop area, maintain design depths on a reduced area, or abandon irrigation on some crops altogether. For example, spreading available irrigation water evenly over the potato crop may result in poor quality (scab, growth cracks) resulting in tubers which will not sell into a quality conscious market (Bailey, 1988). It may therefore, be advisable to irrigate the whole potato crop at the normal application rate at the expense of other crops. A lower output of high quality produce is often better than a higher output of poorer quality produce. The vulnerability of crop yield and quality to water stress, and the price differentials for quality produce, will influence the decision to irrigate some crops at the expense of others. Where

53

water is short, farmers will divert irrigation to other more profitable crops, such as potatoes and vegetables. Farm circumstances influence choice of strategy. There was a preference on relatively small farms producing for sale on the open market rather than against contracts to spread available irrigation water over the existing area of crop, usually in anticipation of rain. Larger or specialist farmers not wishing to place market contracts at risk, preferred to concentrate available irrigation on particular fields and crops to ensure an acceptable supply of quality produce. Preference might also be given to existing good quality which can be maintained. Some farmers reported giving priority to soils with a low AWC (sands) where crop vulnerability is greatest, although licence conditions and abstraction points may limit flexibility in use. All farmers interviewed preferred restrictions on abstraction if these reduced the risk of cessation (although strength of feeling depended on whether they had access to stored water). Some farmers expressed a preference for 50 % irrigation restrictions, with irrigation only at night rather than during the day, as this was felt to be more water efficient. Many large operators already irrigate at night. Some of the smaller farmers dislike night application as this may involve extra capital costs and can increase work load. For some, it would be necessary to invest in new equipment to cope with night-time irrigation. Other concerns included safety aspects associated with irrigators and workers moving at night and the noise impact of irrigation adjacent to residential areas. Benefits from night time spray irrigation relate to improved uniformity of application and to lower evaporation. Evaporative losses, however, are not normally significant in the UK, except in dry years. Wind is the major factor influencing uniformity of application. Research has shown that there are more than 200 % more ‘ideal’ hours with wind speeds below 3 m/s during the night than during the day. Conversely, most ‘unacceptable’ hours (windspeed above 5 m/s) occur during the day (Bailey, 1987). One advantage of irrigating only at night, from the regulators point of view, is that those operating irrigation during the day can easily be seen and therefore checking that bans are not being breached is simplified. Some farmers recognised the public perception benefits of restricting irrigation to nigh time, although this was less of an issue in predominantly agricultural communities.

54

Farmers generally felt that restrictions up to a 50 % reduction in daily abstraction (during the day or night) could be coped with as long as enough warning of the restriction was given. The least favoured restriction option was 4 nights out of 7 at 50 % of the 24 hour rate, which not only limited the daily amounts applied but made scheduling difficult and extended the time intervals between irrigation. A number of farmers reported that they felt more comfortable with a formal restriction fairly enforced rather than one left to voluntary compliance. The above responses reflect short term in season responses.

Strategic responses to the

increased risk of abstraction limits, such as changes in land and water use, irrigation technology, and water storage are referred to later.

4.12 Conclusions and Cautions 4.12.1 Conclusions The conclusions of the preceding case study of the financial impact of restrictions on abstraction for irrigation in the South Level in the design dry year are as follows: •

The financial losses to farmers of cessation and restriction are substantial. The value added by water in intensive irrigated agriculture of the type found in the study area is high by any standards.

•

Much of the benefit of irrigation relates to quality assurance. Unreliable water supplies reduce farmer ability to meet market needs. Buyers will look elsewhere for supplies, and local producers could suffer both short and long term negative consequences.

•

The early introduction of restrictions in order to reduce the probability of complete cessation is a preferred option and makes financial sense. The estimates of the impact of partial restrictions are likely to overestimate actual loss because farmers can adopt strategies to minimise loss by rescheduling to reduce peak demands and to make the most of water available. Given early warning of possible restrictions farmers can adopt appropriate coping strategies.

•

Whilst the detail of water allocation within the farm should be left to the individual farmer, the Environment Agency should recognise that there are substantial differences in potential irrigation benefits between crops and between soil types, and that these differences should feature in water resource management decisions at a catchment level.

•

The approach developed for the South Level has potential for generic application. This is discussed in the next chapter.

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4.12.2 Cautions regarding approach and results The method developed here provides a framework for irrigation benefit at farm and catchment level for water resource conditions associated with the possible introduction of irrigation restrictions. The key assumptions and risks in the method are: •

The research evidence relating to yield assurance and, more particularly quality assurance benefits, is limited for many irrigated crops.

•

The assessment of yield benefits adopted here assumes linearity of saleable yield response to irrigation. In practice this is unlikely, but a better estimate is not available for most crops (with the possible exception of grass). Available research evidence and farmer assessment was used to apportion quality benefits to the timing of irrigation.

•

The irrigation modelling methods used here estimates water stress in terms of short fall in crop evapotranspiration needs. For some, but not all crops, this is related linearly to vegetation yield, but not necessarily to saleable yield.

•

The assessment identifies the need for and benefits associated with spray irrigation to meet deficit in water from rainfall. The effect of sub irrigation by retained ditch levels is ignored but could be substantial under managed conditions.

•

Crop prices and quality premium are based on typical, observed levels, adjusted to reflect conditions in a dry year. The estimates of benefits are very sensitive to these price predictions.

•

The potential yield and quality contribution of irrigation depends on many other crop husbandry and environmental factors. Delivery of adequate water in itself may not guarantee the potential benefits described here.

•

There is lack of information to substantiate actual application depths of water for irrigation. Modelled estimates and farmer data are used but it has not been possible to relate these to actual depths applied in given climatic years. Information regarding actual use of licensed quantities of water is limited. Similar cautions are expressed regarding estimates of the percentage of crops actually irrigated in the South Level in the design dry year.

4.13 Summary This chapter has developed a methodology for assessing the financial impact on farmers of restrictions on the abstraction of water for irrigation and applied this to the South Level in Cambridgeshire. The next chapter examines the impact on-non-agricultural users of the water environment of reduced water levels.

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5.

NON-AGRICULTURAL USES OF WATER

This chapter considers the impact of low water levels or flows on non-agricultural water users and environmental quality. The chapter develops a methodology for risk assessment and economic evaluation and applies this to the South Level case study.

5.1

Environmental Risk Assessment

The approach to risk assessment involves a number of elements: Identification of Action or Intention of Action Possible Consequences of Actions Size or magnitude of the consequences Probability that consequences will occur Risk Assessment (consequences weighted by probability) Risk Evaluation (interpretation of the acceptability/tolerability of the risk) Risk Management

The concern here is with the assessment of the possible consequences to non-agricultural interests of reductions in levels and flows associated with unrestricted irrigation abstractions from surface waters during periods of drought. Unrestricted abstraction could compromise benefits and standards of service to other water users and to the aquatic environment. The approach identifies the interests placed at risk for example, the extent to which they could be affected (magnitude of the impact), the size and significance of the consequences, the probability that the consequences will occur, and the acceptability of the risk involved (that is the acceptability of the consequences/probability outcome). The overall acceptability rating reflects social preference, priorities and tolerance. Tolerance is often influenced more by perceptions of the significance of consequences than by the probability of occurrence. Risk management usually involves costs in the form of the commitment of resources or modifications to operating strategies in order to reduce the probability of damage or loss. The latter can be measured in monetary terms, for example, incomes or asset values per period placed at risk weighted by the probability of the damaging event.

In the case of irrigation

restrictions, constraints are placed on abstractors (with consequences for value-added in farm production systems) in order to protect non-agricultural interests from exposure to unacceptable risks. 57

In economic terms, a rational risk management strategy for irrigation abstraction would balance net income loss to farmers with the benefits delivered to other users. Income losses to farmers due to restrictions, though difficult to quantify precisely, are relatively easy to determine because agricultural inputs and outputs are traded in the market place. This also applies to other water users who produce tradeable goods and services. Many important and hence significant aspects of the water environment, however, involve non priced public goods which are not conventionally traded. These deliver benefits to both immediate users (such as bird watchers) and non-users (future generations who draw subsequent benefit from a protected environment). Valuation of these environmental attributes is not easy. For these reasons, the application of cost benefit analysis to determine acceptable risk strategies may not be sufficiently complete or reliable, especially as many environmental consequences may be unidentified or unquantifiable.

In such cases, the precautionary

principle may apply whereby strategies aim to deliver acceptable levels of risk, usually defined in terms of some minimum environmental quality to be protected, if not at any cost, at least at reasonable cost. (Hence the criteria of Best Practicable Environmental Option (BPEO) and Best Available Technology Not Entailing Excessive Costs (BATNEEC)). The economic analysis switches to one of cost effectiveness analysis.

That is determining the most

economical way of ensuring tolerable risk levels. A key element of risk management involves defining risk thresholds for the range of interests involved. These thresholds will reflect an evaluation of the combined significance and likelihood of consequences of reduced water levels. These thresholds will trigger actions to protect against unacceptable risks. In the South Level the Environment Agency considers that navigation and features of the aquatic environment will be seriously affected if the level at Ely Depot Level Station at TL 560 804 drops below 1.4 mAOD.

5.2

Approach to Assessment

Table 5.1 identifies the types of non-agricultural benefits attributable to the maintenance of levels in watercourses, and by implication the losses incurred if these are compromised.

58

Table 5.1

Non-agricultural and environmental users/interests

59

5.1

60

The table also indicates the degree of vulnerability to reduced water levels and the methods which might be used to determine the economic value of losses (or the cost of damage avoidance). Two related methods have been used to assess non-agricultural impacts, namely risk assessment and environmental evaluation. These are summarised in Table 5.2. Table 5.2 Sector

Summary of methods for assessing the impact of changes in watercourse levels on non-agricultural users and environmental quality Benefit Type

No of Users or characteristic

a Risk Assessment Method Eg Industry Use Industry

High=3 medium=2 low=1

Economic Evaluation Method Licensed quantities 000m3/period

5.2.1

Unit value of user benefit/ characteristic placed at risk (consequence of impact) b

Vulnerability Rating (probability of occurrence)

Risk Rating and Assessment

c

a x b x c=d

High=3 medium=2 low=1

High=3 medium=2 low=1

Cost of mains water £/m3, net of savings in abstraction charges

probability 0.01

1

Risk Class and Evaluation

High=18-27 medium=8-12 low=1-6 zero=0 Expected value £/period

Refer to expected value

Risk Assessment

The risk assessment approach adopts a simple scoring system which combines, for each benefit type, information on incidence of water user or environmental characteristic, unit value, degree of vulnerability, and a measure of risk which can be evaluated in terms of significance and tolerance. Risk assessment is based on determining whether or not the risk to each benefit type is high (scores 3), medium (scores 2) or low (score 1). Once the scores have been calculated, a further step is to determine whether any of the water users present relate to any statutory or other legal requirements of the Agency. For example, there is a legal duty on the Agency to maintain some rivers as navigable and to protect EC designated fisheries. Those benefit or user types associated with a statutory duty are highlighted. The output of the risk assessment, therefore, is to focus attention on the statutory and ‘high’ risks in a catchment. It is these water uses for which tolerable minimum levels should be determined. It is also possible to aggregate the scores of the risk assessment to obtain a total score. For example, the maximum score which could be derived for any particular river (set of rivers) is 61

1,080 (where this is the sum of risk scores of 27 across all 40 impact categories). An overall rating of 720 to 1,080 gives a high risk classification for the catchment area. A rating of moderate risk would relate to a score falling between 360 and 720, while an overall rating of low risk would fall below a score of 360. However, a high aggregate score could be achieved by a high diversity of non-agricultural water users and environmental impacts, whereas a less diverse set of impacts could score less even though the individual impacts in themselves are very significant. For this reason caution is recommended in adopting such an approach A detailed explanation of the scores used are presented in Section 5.3. Users of this method should use some discretion in applying the magnitude and sensitivity scores to allow for site specific considerations. 5.2.2

Economic Evaluation

The second method builds on the first by using standard monetary estimates for valuing consequences to water users and the environment and estimates of the probability that the consequences will occur. The outcome is an expected economic value which can be placed in a cost benefit analysis. Caution must be taken in using these economic values. The benefit values used have been derived in study areas of different characteristics. When transferring these value to other sites an assessment should be made as to whether they are reasonable given the characteristics of the site. The Economic Evaluation is based on the Low Flow Alleviation Benefit Assessment Guidelines (1997) and users of this method should refer to these guidelines for more details. Both of the methods above require an estimate of the probability of low water levels affecting water users if current spray irrigation abstraction is unrestricted. Figure 5.1 has been created to help describe the relative vulnerability of water users and environment quality to reductions in water levels.

Where data exists the diagram has been used to provide an objective

assessment.

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Figure 5.1 Vulnerability of non-agricultural water users and environmental quality to reduced water levels Water levels as % of normal level normal

Probability of occurrence

Risk class

ecology (aquatic & bankside plants, fish) 75%

3 0.50

angling in-stream recreation 50% commercial fishing ecology (birds, amphibians)

industry/hydro-power waste emmiters

25%

dry

5.3

3 0.30

0%

2 0.15

landscape & archaeology out-of-stream recreation flood defence

1 0.05

Assessment of Impacts

The following sections consider the main impacts of low levels in watercourses by benefit type. The assumption is that the long term frequency of over abstraction and reduced levels is low and that the impacts on water users are short term and non permanent, affecting revenue, operating costs, or enjoyment as the case may be in the period concerned. Impacts and responses of those affected are viewed in this context. If reduced levels became a more frequent phenomena, impacts and response might be different. For instance water abstractors might seek permanent alternative supplies or invest in water recovery or treatment facilities to reduce the impact of low levels and flow. Some sensitive features of the environment such as on aquatic flora, however, may incur impacts beyond the immediate period of low levels. The results of the risk assessment and economic evaluation for the South Level are presented in Tables 5.3 and 5.4.

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Table 5.3 Sector Industrial Abstraction

Assessment of environmental risks associated with reduction with water levels and flows in rivers and watercourses, South Level Type

No. of Users/ Magnitude Probability Risk Statutory Risk Units of Value of Occurence Assessment Duty () Class Sand & Gravel washing 0 0 0 0 Industrial 3 2 2 12 Moderate Industrial - misc 0 0 0 0 Non-consumptive cooling 3 2 2 12 Moderate Consumptive cooling 0 0 0 0

Hydro-power Water mills hydro-power turbines

0 0

0 0

0 0

0 0

Commercial Trout Fisheries Salmon Carp Crayfish

0 0 0

0 0 0

0 0 0

0 0 0

Flood defence Flood risk

3

3

1

9

Moderate

Waste Waste emmiters Assimilation

3

2

2

12

Moderate

Angling

Coarse Non-migratory salmonids Migratory salmonids

3 3 0

3 3 0

2 2 0

18 18 0

 

High High

s s

In-stream recreation

Boating Canoeing Sailing Water sports

3 2 1 2

2 2 2 2

3 2 3 2

18 8 6 8



High Moderate Low Moderate

s

Out-of-streamFootpaths recreation Bridleways Parks

3 2 1

2 2 2

3 3 3

18 12 6

Moderate Moderate Low

Archaeolgical SAMs

2

2

2

8

Moderate

Aesthetics

AONB/Large watercourse

3

2

1

6

Low

Nature Plants aquatic conservation Plants bankside Species Invertebrates Fish Amphibians Reptiles Birds Mammal Habitats Floodplain grazing marsh Fens Reedbeds Raised bog Mesotrophic standig water Eutrophic standing water Chalk rivers

3 3 2 2 2 1 2 1 3 3 3 0 0 0 0

3 3 3 3 2 1 2 2 3 3 3 0 0 0 0

3 3 3 3 2 1 2 2 3 3 3 0 0 0 0 Total

27 27 18 18 8 1 8 4 27 27 27 0 0 0 0 363

High High High High Moderate Low Moderate Low High High High

s s s

Moderate

s

  

0 = no record, 1 = low, 2 = moderate, 3 = high Risk Class column 0 = no record, 1-6 = Low risk, 8-12 = Moderate risk, 18-27 = High risk, s = statutory duty ‘High’ and s indicate those water uses which should be considered as priorities. Total score 1,080-720 = High, 720 - 360 = Medium, 300, Tcma 2 = 100 - 299 Tcma and 1 < 99 Tcma. The value of water to an industry and thereby the impact supply curtailment were assessed in terms of 3 = high, 2 = medium and 3 = low. The probability of low water levels affecting industry if irrigation abstraction is unrestricted was classed as 3 = > 50 % probability, 2 = 10 % - 50 % probability and 1 = < 10 % probability. As the value of water as an input to industry is often quite low, it is assumed, as presented in Table 5.3, that the impact of low water levels is medium and the probability of occurrence is also medium. 66

Economic evaluation In order to obtain an economic value for losses to industry due to low water levels, the licensed quantities for industrial abstraction were identified, 384.33 Tcma for industrial purposes and 522.79 Tcma for non-consumptive cooling. It was assumed that low water levels would occur for less than 6 months per year, so only half the licensed quantities were considered, although it is recognised that some industrial uses are seasonally concentrated such as vegetable washing. The licensed quantities were multiplied by the cost of using an alternative source of water, such as mains water (£0.46 m3), less savings in industrial abstraction charges to provide an economic value of losses to industry. 5.3.2

Hydro-power

Water power such as hydro-electricity and water mills are used for energy generation. Within the South Level water mills are located at Clark and Butchers Mill at Soham, situated on Soham Lode and Parkers mill situated on the River Lark. However, these mills are not in working condition so an assessment of hydro-power for the South Level was not required. Risk assessment To assess the risk to hydro-power in a catchment, the number of water mills or hydro-power turbines in the area are separately identified, and their MW ratings recorded. In the UK, hydro-power plants in irrigated areas are likely to be small installations. The total aggregated power output is expressed as one of three classes, 3 = 5 MW - 1 MW, 2 = 1 MW - 50 kW and 1 = 3 mills, 2= 2-3, 1=1). The magnitude of impact is classed as 2=medium, and probability of occurrence rating is 2= medium. Economic evaluation The total aggregate kilowatt output of electricity generating sites within a catchment is ascertained and weighted by the proportion of the year during which generation is affected by low water levels. This is multiplied by the price per kilowatt of electricity to give an estimate of financial loss, net of savings in the running costs of the mill or station. Where mills are

67

used as tourist attractions, the power costs of running them artificially may be ascertained based on kW rating. 5.3.3

Commercial fisheries

The main commercial fisheries in England and Wales produce rainbow trout. Carp and salmon farming is of less national economic importance. Salmonids, such as trout and salmon require continuous water exchange to maintain appropriate water quality. In the summer there is often a four-fold increase in the amount of water needed to carry the same stock as in the winter. Other fish, such as carp are reared in standing water. Within the South Level there are no commercial fish farms although some commercial eel fishing takes place along the lowland fen sections of the rivers, particularly in sections of the Ely Ouse which are owned and leased by the Environment Agency. Commercial eel fishing is carried out principally between April and October. Eels move from the sea to rivers where they are caught by fishermen using dutch fyke nets. Eels are not very sensitive to low water levels. However, there could be a loss of revenue to the eel fishermen if the eels move elsewhere, assuming they are not caught. Risk assessment To assess the risk to commercial fisheries of low water levels/flows, the number of abstraction licences for fishery purposes and the licensed quantities are obtained from licence records, together with information on the type of fish farmed. The licensed quantities are graded into 3 classes, 3 = > 100 Tcma 2 = 99 - 51 Tcma and 1 50% probability, 2 = 10% - 50% probability and 1 = < 10% probability. Economic evaluation Economic losses to commercial fisheries as a result of low flows are calculated in terms of restocking costs associated with fish mortalities. Expected fish mortalities under low flow conditions can be expressed as a percentage of normal stocking rate and costs of restocking ascertained accordingly. 5.3.4

Flood defence 68

Low water levels/flows may impact on flood defence structures, causing structural damage over time. Low lying areas which are particularly prone to flooding will be at a greater risk from failure of flood defence structures, especially where river systems are embanked and carry highland waters. The South Level is a low lying basin at risk to flooding and has a 1 in 100 year standard of protection. The Denver Sluice Complex controls all the flows from the catchment as well as controlling the retention in the South Level ponded section. Denver Sluice also provides protection to the South Level from the tidal river. The Cut-off channel from Barton Mills on the River Lark to Denver and raised embankment along the Ely Ouse, Lark and Little Ouse have been constructed as part of a flood protection scheme in the area. Risk assessment The flood return period for the South Level was identified and graded into one of the following classes 3 = > 20 years, 2 = 19 - 6 years and 3 = < 5 years. The impact of low water levels on flood defence structures in the South Level was rated in terms of 3 = high, 2 = medium and 1 = low, and considered high in this case. The probability of a flood event due to low water levels damaging flood defence structures was estimated in terms of 3 = > 50% probability, 2 = 10% - 50% probability and 1 = < 10% probability. The assessment gave a rating of 1 in this case. Economic evaluation The economic cost of low water levels on flood defence was assessed in terms of the land use in the catchment and expressed as Household Equivalent (HE) values (see NRA’s Flood Defence Management Manual, 1995). From 6 categories of land use the dominant land type in the South Level was selected. This has a household equivalent per km value of 15 assigned to it which was multiplied by the length of river in the catchment (158km). This was then multiplied by the household equivalent value of £1,261. The probability of a flood event occurring as a result of low water levels was determined and multiplied by the total HE value to derive an economic cost for a flood event in the South Level as a result of low water levels. Flood defence managers in the South Level reported that low levels in watercourses could require an additional cut of channel vegetation. Maintenance cost could double in low flow years. 5.3.5

Waste assimilation 69

Discharge consents issued by Environment Agency allow water users to emit waste to watercourses which, in the event of low water levels/flows may increase the concentration of pollutants in the water. Alternative methods of disposal or pre-treatment may be required. However, in many locations output from sewage treatment works comprises the majority of the base flow in rivers and without this flows would be further reduced. In the South Level approximately 25 discharge consents are issued of which 18 are for main sewage treatment works operated by Anglian Water Services. Risk assessment To assess the risk to waste emitters of low water levels the number of discharge consents issued in the catchment area were identified and graded into the following classes 3 = >20, 2 = 11 - 19 and 1 = 50%, 2 = 10% - 50% and 1 = 70 %, 2= 69%- 21%, 1 = 50%, 2 = 10% - 50% and 1 = 300, 2 = 100-300, 1 = 200, 2 = 100-200, 1 = 100, 2 = 50-100, 1 = 100, 2 = 50-100, 1 =