Irrigation practices and water conservation opportunities in Migina Marshlands D. Nahayoa*, U. G. Walia, F.O.K. Anyemedua Faculty of Applied Sciences, NUR, PO. Box 117, Rwanda
Abstract With a growing world population and the need of food security, irrigation practices have a vital role to play worldwide. Climate changes with rainfall variations during all or part of the year require irrigation water conservation practices. Despite being a country of great lakes and the headwaters of two greatest African rivers, the Nile and the Congo, Rwanda is a water scarce country. Rwanda has about 165000 hectares of marshlands in which only 94000 hectares are in use, but some of them are not used wisely. About 90% of the rural populations are farmer; however, they do not produce enough food to satisfy their needs. This is due to the continuous use of traditional, subsistence and inefficient farming practices which are mainly rain fed. Irrigation is practiced mainly in the marshlands using the inflows into the marshlands. Over the years, the marshlands are becoming less productive, with visible signs of fertility decline. This trend could be attributed to irrigation practices in the marshlands, which tend to drain the marshlands instead of conserving the water. This research aims at studying the current irrigation practices in the marshlands and looks for opportunities of water and nutrient conservation to restore the fertility for improved food production. Using questionnaire to the stakeholder at all level, statistical and hydrological analyses of the existing and acquired data, this study could bring about the promotion of irrigation water conservation practices in the catchment. Seasonality and topographic conditions, with accompaniment of erosion, flooding and drought problems, are discussed to show how rehabilitation and redesigning and reinstallation of new irrigation structures, better maintenance of irrigation structures and introduction of improved irrigation systems in the catchment could contribute to land protection and increase food production. Rainwater harvesting to be used for irrigation during the dry season, groundwater recharge by using boreholes are added to the possible solutions to ensure environmental protection and improvement of irrigation water conservation practices in the catchment. Finally, ways in which irrigation water conservation practices could be utilized are explored as well as possible impediments that might be encountered. Keywords: Environmental protection, Food production, Groundwater recharge, practices, Rainwater harvesting.
1.
Irrigation water conservation
Introduction
Agricultural water management is vital to food security, poverty reduction, and environmental protection worldwide. Climate changes with rainfall variations during all or part of the year require irrigation water conservation practices. Rwanda is one of the great lake countries and has a lot of water resources. Agriculture employs about 80% of the population and provides over 40% of the GDP of the country. Population density of Rwanda is about 305 persons per square kilometer with a growth rate of about 3.5% ( MINIPLAN, 2002).The area under cultivation is about 1,385,000 hectares, which is 52% of the total surface area of the country (MINAGRI, 2003), and the population cultivates even the marginal areas in trying to satisfy their needs in food security. The population is growing but the arable land does not increase. To feed the rapidly growing population, there is a need to increase agricultural productivity in the country. *
Corresponding author. Tel.: +250 08678702; fax: +250 530210. E-mail address:
[email protected] (D. Nahayo)
2 This can be achieved by a change in agricultural practices. Rwanda has about 165,000 hectares of marshlands in which only 94,000 hectares are in use (MINAGRI, 2003). In addition, the used marshlands are not used wisely or exploited in the appropriate manner. Erosion, lack of maintenance of irrigation structures and misuse of available water resources in agricultural activities impose a problem of food security and water and land conservation in the country. Migina, one of catchments of the south province of Rwanda, is faced with problems of erosion and flooding in the main rainy season (from mid-February to the end of May ) and water shortage in the main dry season(from June to mid-September)adding to lack of better maintenance of its current irrigation systems. This study looks at the promotion of irrigation water conservation opportunities in Nyaligina, Nyamugali, Rwasave and Ndobogo, marshlands of the Migina catchment. It begins by evaluating the current irrigation practices in these four marshlands and identifies potentials for improved hydraulic performance. This could help for improvement of the standard of living and environmental conditions in the study area so that land and water will be manageable in a sustainable way.
2. Materials and Methods 2.1. Literature Review Irrigation practices are the techniques of applying an amount of water to the soil in the aim of controlling of water application to arable soil, supplying crop water requirements not satisfied by rainfall, providing crop insurance against short duration droughts, etc. Irrigation methods are summarized into three types which are surface (flooding, furrow and surface drip irrigation), subsurface drip irrigation and overhead irrigation (sprinkler irrigation or hose- end overhead sprinkling). Relative moisture varies the most in furrow irrigation and the least in drip irrigation systems (Texas Water Development Board, 2002). Irrigation water conservation opportunities are defined as the structural improvements in the application systems, better maintenance of existing irrigation systems, altered tillage and soil management, changes in the crops grown, water harvesting to be used in drought season, improved hydraulic performance in the irrigation scheme etc. (Ley, 2003). Efficient agricultural water conservation practices are essential to ensure the viability of water to be used in drought season or in other activities (Texas Water Development Board, 2002). Structural improvements in application systems include practices such as introducing infiltration ditches or replacing open ditches with underground pipe, lining ditches, use of gated pipe, fitting gated pipe systems with surge-flow devices, conversion from furrow to sprinkler irrigation or drip irrigation and installation of tailwater recovery systems. The objective of adopting these practices is to increase application efficiency and to apply conflict management system at farm levels (Texas Water Development Board, 2002). In many instances, they also have the potential of decreasing nonbeneficial consumptive use. Similarly, structural land improvement such as construction of infiltration ditches, terracing structures, the digging of boreholes for reducing runoff on high hill slopes and recharging groundwater, afforestation, antierosive planting and river beds enlargement and land leveling are designed to improve application efficiency, decrease nonbeneficial consumptive use and to reduce the soil degradation by erosion (Allen, 1991; Boyd at al., 2000). Water conservation and soil management are practices designed to increase application efficiency at the farm level (Evans, 1998). Water conservation involves techniques that allow growers to schedule irrigation based on moisture needs of crops. Specific techniques include monitoring soil moisture and maintaining daily
3 records of crop water balance using estimates of consumptive water use from weather data. Use of furrow irrigation and practicing more timely fertilization are examples of altered tillage and soil management. Water conservation techniques can also be used to schedule strategic deficits in water availability during periods when crops are relatively insensitive to soil water deficits. This form of water conservation is generally referred to as deficit irrigation, and results in decreases nonbeneficial consumptive use. Changes in cropping patterns can result in decreases nonbeneficial consumptive water use. Some conservation measures can be implemented at the system level to improve overall application efficiency within a catchment and, in some cases, decrease nonbeneficial consumptive use (Colorado Water Resources Research Institute, 1996). Rainfall data which are used in irrigation water conservation opportunities are treated using Orstm method for large catchments and rational method for small catchment with a surface area not greater or closed to 5 km2 (Daniill at al., 2005). Using surveys and statistical analysis of all information gathered give idea of finding solutions of an improved hydraulic performance (Skogerboe and Merkley, 1996). 2.2 Study area description Nyaligina, Nyamugali, Rwasave and Ndobogo marshlands are located upstream of Migina catchment in south province of Rwanda and situated in the three first subcatchments of Migina: The small subcatchment A of 3.14 km2 which is drained by Rwantarama river and closed by Rwasave earth dam; The small subcatchment B of 3.39 km2 which is drained by Kazibaziba and Nyamugali rivers; The large subcatchment C of 37.50 km2 which are drained by Ndobogo, Nyagashubi and Kidobogo rivers with Nyakagezi, Nyabitare, Musizi and Kabacuzi as tributaries; The climatic rhythm is the followings: i. A small rainy season from mid-September to mid-December; ii. A small dry season from mid-December to mid- February; iii. A great rainy season from mid-February to the end of May ; iv. A great dry season from June to mid-September. The main agro-climatic parameters which are the temperature, radiation, potential evaporation and hydrous regimes that influence crop production (Hargreaves and Merkley, 2004), as they are derived from the stations of Butare (2°36' S, 29°44'E; 1,768 m) and of Rubona (2°29' S; 29°46' E; 1,706 m) for the thermal parameters, are favorable to agricultural activities. The only problems which decrease crop production are erosion and flooding in the great rainy season and water shortage in the great dry season. These could be the results of the topographic conditions with a slope which varies between 2 and 3%, rainfall distribution and variation along the year (109 to 127mm in the great rainy season and closed to zero in the great dry season 7mm (AHT, 2003)), deforestation and of anti-erosive structures and inadequate irrigation water use. The rainfall and hydrous patterns are characterized by an annual rainfall of about 1,170 to 1,270 mm, the rains are concentrated between September and the end of May. April is the rainiest month but the highest amount rain fall during the November to December raining season. November and the period from March to May are sprinkled. The small dry season of DecemberJanuary, observed relatively well in many other parts of the country, is less clear in Migina, because in the least rainy stations of the zone (Save and Rubona) the average rainfall of December and January remains closed or ranked even above 100 mm. The annual average of the relative soil moisture, calculated over the 11 last years is 75.7% with minima in June of 59.8%
4 and the maximum in April of 86.3%. The annual average of evaporations in the area is 917.2mm. Maximum evaporations are during the months of main dry season (June to September) with monthly evaporations going from 80 mm to 120.9 mm (August). The winds speed mostly between 1 to 3m/s and rarely exceed 6 m/s. There is one well marked dry season and an important hydrous deficit between June and the beginning of September. The first rains of September are relatively not very useful for agriculture because of their irregularity and in addition it fall on a hot and drained surface and get evaporated immediately It will be necessary to envisage irrigations between June to beginning of September to safeguard an optimal agricultural production in that season. The only alternative in the event of lack of water to cover this deficit is to adapt the farming calendar and to introduce crop that demand less amount of water. 2.3. Compilation of existing information The first step in this study was to compile existing information about irrigation systems in the marshlands. Some general maps of the project area as well as detailed design maps of the catchment have been collected. Technical reports, socio-economic studies that have been written regarding the project, have been studied. Information regarding difficulties with irrigation practices has been obtained from different groups of farmers scattered throughout the marshlands. Using questionnaire, much have been learnt from the farmers. Here, information has been gathered primarily by asking people questions either by having interviews ask questions and record answers or by having people read or hear questions and record their own answers. Information has been sought from ISAR, RADA, etc, institutions, charged with responsibilities over water and land in Rwanda (ISAR, RADA, etc.). All the information gathered in this step provide the background of the projects and helps the study of irrigation water conservation practices in the study area. 2.4. Identification of irrigation structural damages The second step in this study was conducting field inspection and surveys in order to identify problems related to irrigation structures, its condition, performance and maintenances, for proper quantification allow taking appropriate intervention measures. In case of structural damages the causes are properly assessed for appropriate mitigation.
2.5. Data gathering, handling, analysis and interpretation of the results All the information from the first and the second steps was primarily gathered in packages according to the data type and treatment model and secondly handled. As the agricultural use of the land of the marshlands is related to the availability of water in the catchment, the hydrological or rainfall data were used to estimate the expected maximum amount runoff and base flows, that are used for the design or redesign of some irrigation structures (e.g. channels, dams, weirs, etc.) taking into account the topographic conditions for compliance with Lacey’s regime theory. Average monthly rainfall and the Orstom and Rational methods were used for discharge estimation. The determination of irrigation crop water requirements and the irrigation supply requirements in comparison with the available water in the stream or in the reservoirs was used to suggest the method of water delivery and engineering alternatives. The irrigation water demand
5 was calculated, by considering all surface areas which are irrigated in the marshlands for all crops: rice, maize, sorghum, Irish potatoes, suit potatoes, cabbages, beans and others according to the available data or by using data from (FAO, 1979). Questionnaire were also analyzed. Data for this study were collected from smallholder irrigations farmers of, Nyaligina, Rwasave, Nyamugali and Ndobogo, the upstream marshlands of Migina catchment located in the south province of Rwanda. A stratified sampling method was employed to the smallholder irrigation farmers. Taking into account the cost considerations, the deadline of submission of the study and others limiting factors, sample of 100 farmers was interviewed using a structured questionnaire set in the local language. In trying to study how to improve irrigation water conservation practices in the survey area, two methodologies were used to investigate farmer’s views on irrigation water use, their contribution and the intervention of agricultural institutions for improved hydraulic performance in the marshlands: • Structured interviews on all technical, managerial and irrigation support services participation issues were carried out; • By using Statistical Packages for Social Sciences software (SPSS), descriptive statistics were developed to describe, the farmer’s views on irrigation practices, crop production and water use efficiently in the marshlands. The field visits of structural damages were added to the information from questionnaire analysis to find the normal, catch-up and preventive maintenances in the irrigation scheme. In addition, possible solutions for improved hydraulic performance in the catchment and strategies for attaining irrigation land and water conservation in a manageable and in a sustainable way in all the marshlands would be established. Finally, all information from data analysis would be summarized to conclude and make some recommendations to the stakeholders at all levels. 3.
Results, analyses and discussions
3.1. Hydrological data analysis( Annex 3-9) The agricultural use of the soil of marshlands is related to the availability of water in the catchment and thus the hydrological regime of the marshlands determines the water resources which can be used in irrigation scheme. This has been explained in the study area description. The hydrological study aims at two things: firstly, the determination of the storm runoff for the required frequencies and secondly, determination monthly average flow with the level of the hydrographic network of the catchment area in which the marshlands is located in order to determine whether the water requirements of crops can be met at the various cropping seasons of the year. Considering the scarcity of direct measurements, indirect estimation methods were used to determine certain parameters which are validated by observations on the field. In the absence of other hydrological data, rainfall records were used as a basis for the hydrological study. The Butare Airport’s rainfall records (latitude 02°36’ - longitude 29°44’ - altitude 1760 meters) were used for reference for the study area. In this study, the rational method was used for pick runoff estimation for the small subcatchment (with the surface area not greater than or closed to 5 km2) and the ORSTOM method of runoff estimation was used for the large subcatchments. In the rational method, the Kirpich formula was used to estimate the time of concentration (the time required for the farthest point of the catchment to contribute to runoff), and is given by Eqn. 1.
6
tc =
0.0195L0.77 , Kirpich formula (Daniill et al., 2005) S0.385
(1)
Where tc is the time of concentration in minutes, L is the maximum length of the flow in meters, H is the difference of both upstream and downstream altitudes of the catchment in meters and S is the watershed gradient in meters/meters of the difference in elevation between the outlet and the most remote point divided by the length L (H/L). The formula for peak flow Qp is given by Eqn. 2. Qp= 0.278*C *i* A, (Daniill et al., 2005)
(2)
Where C is the runoff coefficient, i is the rainfall intensity during the return period tr and A is the catchment area. The value of i is assumed constant during tc and the peak flow or maximum discharge continues until the end of the rain. In the ORSTOM method the assumptions remain the same, but the peak flow or maximum discharge is given by Eqn. 3. Qp= K*M, (Daniill et al., 2005)
M=
(3)
(K r * Vp ) TB
Vr = Kr *Vp Vp = a *H*A Where: •
H is the depth of the punctual rain determined by Gumbel adjustment for the rain gauge of reference Butare;
•
Vp is the total volume of rainfall on the catchment;
•
Kr is the runoff coefficient;
•
Vr is the effective volume of runoff;
•
Tr is the return period in yeas;
•
TB is the effective duration of runoff; and
•
K is the independent coefficient determined by experiment and is equal to 2.5 in the ORSTOM method.
3.2. Irrigation crop water requirement and water use analysis The irrigation water demand is calculated, by considering all seasonal surface areas which are irrigated in Migina catchment for all crops: rice, maize, sorghum, Irish potatoes, suit potatoes, cabbages, beans and other.
7 The volume of water used in agricultural sector in Migina marshlands is about 80% of the total surface water abstraction. The net irrigation is defined as amount of water required to be supplied to the crop in order to satisfy its consumption use. This was calculated by using Eqn. 4. Inet= Kc* ETo-Peff, (Michael, 1999)
(4)
And the gross irrigation is given by Eqn. 5: Igros=
K c * ETo - Peff , (Michael, 1999) ef
(5)
Where Inet= net irrigation requirement Kc= crop coefficient ETo = reference evapotranspiration Peff = effective rainfall Pm=monthly precipitation D=daily interception threshold − 1.76 * D Peff=Pm*Exp ( ) Pm0.45 and ef is the global efficiency. The global efficiency is 80% of water abstraction, and the pan coefficient Kpan is 0.70 (FAO, 1979). The daily interception threshold is calculated by using the mean of all the daily interception thresholds applied to all crops; D equals to 0.73. Irrigation water demand studies undertaken in Migina marshlands before this study have been generally done well; however, the problems have been how to implement the recommendations using the required water for irrigation and save an amount to be used in drought season. 3.3.Irrigation practices and irrigation structures analysis The surveys and field visits which have been undertaken in the study area have enable us to divide the area into two zones: The first zone is the marshlands of Nyaligina and Rwasave which are well arranged. This study shows that Nyaligina marshland has 39ha while Rwasave marshland has 80ha under irrigation. The study shows that the irrigated area uses flooding irrigation for rice crop production whereas other crops like beans, potatoes, sorghum etc. are irrigated naturally by rainfall according to the weather conditions. The most part of these marshlands are arranged. However, there are many problems with the irrigation structures. Rwasave earth dam with a total reservoir capacity of 100,000 m3 and its useful volume of 85,000m3 needs rehabilitation. Two side intakes of Rwasave earth dam must be rehabilitated by replacing valves and clearing out weeds in all channels and other irrigation structures. The left intake does not function any more and must be repaired. Channels, over 86 intakes and about 40 chutes must be completely rehabilitated. Rwasave bridge must be rehabilitated. The second zone deals with Nyamugali and Ndobogo marshlands which are not arranged at all. The surveys show that Nyamugali marshland has a surface area of 17ha and Ndobogo marshland has a surface area of 67ha under irrigation. The surveys have found that there is a need of
8 improvement of irrigation and drainage systems. The field visits and discussions with the farmers by using questionnaire analysis have helped to identify the following major issues for improper water and land utilization. Illegal canals cutting Farmers at the Ndobogo marshland reported that the upstream people divert water according to their own wishes without consideration to those downstream. The canals are broken at several points and water is being illegally diverted. The farmers at downstream do not receive enough water for their crops. Also, they reported that the farms which are far off the river do not have channels to feed the crops. Farmers have not any facilitative means of feeding water to the crops, especially for rice crop production. Illegal canals cutting have been identified in Nyaligina and Rwasave marshlands. These problems of canals cutting are the source of underdevelopment of most irrigated lands. Irregular blockage of water by uncontrolled farmers to keep the irrigation water supplies confined to their farms is another problem. This practice not only skewed the distribution of irrigated area but also resulted in wastage of huge investment made on the construction of water channels, which remain almost dry, especially in great dry season. This is attributed to lack of weekly rotational schedule, and insufficient field staff to operate these correctly including monitoring for irregular blockage of irrigation water along canals. Equity in water distribution is very important factor for the management of water resources (Ahmad, 1999). Inequity in water distribution results in frustration, lack of interest in farming and maintenance of watercourses, distrust among water users and disputes over water rights among the users. Inequity in water distribution is the result of nonfunctional water user associations (Ali and Chuddar, 1996; Hussain and Perera, 2004). Improper maintenance of watercourses, poor field channels and inadequate hill slopes protection In Ndobogo and Nyamugali marshlands, watercourses are poorly maintained. Channels are filled with sand and bushes and water overtops the watercourses, especially in rainy season. Watercourses are broken at several places and cleaning of watercourses is not done any more. The designed outlets at several points are broken which reduces the supply of water available to farmers at the tail end of the canals. The proper repair and maintenance of these watercourses is very important for getting long-term benefits of the investment made on irrigation structures. Due to cheap water availability and lack of knowledge, uncontrolled flood irrigation is commonly used. The field channels are earthen, not designed and not constructed properly and are poorly maintained. As a result, considerable amount of water is wasted in the field channels. Due to undulated fields, huge amount of water is wasted. There is need to level these fields, so that scared water could be used efficiently. For doing so, rehabilitation and reinstallation of the conveyance systems, field adjustments, improvement of circulation roads and bridges, construction of Ndobogo earth dam, which has the following characteristics: 50,000m3 of useful volume, 140m of length, 32m and 4m of bottom and top width respectively and maximum height of 5.5m, for irrigation water storage and flood control; the construction of Nyamugali weir for raising water level upstream of the marshlands in order to construct the main channels on the height which dominates all the irrigable land of the marshlands and introduction of anti erosive structures such as the installation of infiltration ditches and terracing structures, the digging of boreholes for reducing runoff on high hill slopes and recharging groundwater, afforestation, antierosive planting and river beds enlargement could contribute to land and water conservation. By using Orstom and rational methods of maximum discharge estimations and considering topographic condition, we have calculated the main emitters or drains in the marshlands. The
9 irrigation water demand was calculated, by considering all seasonal surface areas which are irrigated in Migina catchment for all crops: rice, maize, sorghum, Irish potatoes, suit potatoes, cabbages, beans and others. We have supposed that volume of water used in agriculture sector in Migina marshlands is about 80% of the total surface water abstraction. The net irrigation was calculated as amount of water required to be supplied to the crop in order to satisfy its consumption use. Proposing two seasons of rice production from September to December and from February to May by using flooding boarder irrigation and introducing furrow irrigation for other row crops such as maize, beans and sorghum, and rearranging fields by respecting the maximum slope of 0.5% and introducing chutes where topographic conditions do not permit that maximum slope could contribute to water use efficiently and land conservation. No organized water user associations and incompetent agricultural support services Water regulation is under established organization in Rwanda, however, water user association are not organized and do not functioned properly. There is no formal body to look after the watercourses and irrigation structures in Migina catchment so that there are many problems among the farmers on water distribution according to priorities. So, There is therefore the need to strengthen and empower water users associations to maintain and improve watercourses along with more effective use of water through improved water management practices (Skogerboe, 1996). In addition competent agricultural support services play a pivotal role in the motivation of farmers towards the formation of water user association, adoption of improved irrigation and water conservation practices, and introduction of high yield crops, efficient water use and proper use of non-water inputs. However, it was observed that irrigation support services work hardly in the catchment. Similarly, On-Farm Water Management activities are limited in these marshlands. Improving agronomic and farm water management practices, particularly promoting the use of improved varieties of seeds and enhancing the role of extension services to farmers for dissemination of up-to-date knowledge are very important to improve land and water productivity (Hussain and Perera, 2004). A good coordination and integrated approach by On Farm Water Management and Agriculture Extension Department is needed, starting with operation, maintenance of main watercourse and field channels for overcoming inequities that occur along the watercourse and assisting farmers with improved irrigation and agronomic practices (Skogerboe, 1996; Early et al., 1976). Thereafter, the current agricultural, water resources and environmental management institutions which are responsible for of the promotion of irrigation practices, water and environmental protection have to sit together and study how to increase food production with an acceptable range of land degradation principles.
4.
Conclusion and recommendations
It is a common place to say that rehabilitation and repairing irrigation structures, installations of new irrigation structures or improved technologies of water saving and land conservation are sufficient to reach an improved hydraulic performance. As it is said that prevention is better than cure, the proposed solutions for finding an improved hydraulic performance in Migina marshlands need an additional, systematic and periodic maintenance of all infrastructures in the catchment. In most cases, farmers are interested in operations, not in maintenance, but may be willing to pursue an effective maintenance program if they have control over water deliveries. Best operated irrigation systems in the world are managed by farmers, not by the institutions in charge of irrigation. However, farmers who are not experienced in the management of their
10 system cannot be effective overnight. They need to go through an evolutionary process of developing management skills. This is where institutions in charge of irrigation have to train and equip farmers with skills to manage, operate and maintain irrigation systems. The training should begin with the heads of water users associations on irrigation maintenance. The most important stage in irrigation maintenance is the preventive maintenance. These chiefs would also train other people on how to improve hydraulic performance in the catchment. The institutions in charge of irrigation have also to work together formally or informally with the water users associations. In addition institutions in charge of irrigation could arrange and give on loan basis selected seeds to the farmers, and allow them to pay after harvesting. Communication skills have also to be developed between irrigation institutions, staffs of water users associations and farmers for better mutual understanding in order to maintain a sustainable improved hydraulic performance in the catchment. Finally, this study has been done in only four marshlands of Migina catchment. It would be interesting to see an extension of the study in other marshlands, not only those of Migina, but also in all Rwandan marshlands. The implementation of the recommendations of such studies could improve the standard of living and environmental conditions in the rural area through improved and sustainable water and land management.
5. Acknowledgements
The study was conducted with the financial assistance from National University of Rwanda in association with UNESCO-IHE, the Netherland Institute for Water Education based in Delft.
6. References
Ahmad, S. (1999). Achievements and issues of irrigation in the 20th century. In: Chandio, B.A. (Ed.), Proceedings of The National Workshop on: Water Resources Achievements and Issues in 20th century and challenges for the next millennium, Pakistan Council of Research in Water Resources, Islamabad, Pakistan, pp. 188–201. Ali, A., Chaudhary, M.R. (1996). Water conveyance and distribution at watercourse level. In: Khalid, R., Robina, W. (Eds.), Tertiary Sub-System Management. International Irrigation Management institute, Lahore, Pakistan, pp. 12–23. Boyd Charlotte and Cathryn Turton, January (2000). The Contribution Of Soil And Water Conservation To Sustainable Livelihoods In Semi-Arid Areas Of Sub-Saharan Africa. Chanson Hubert (2004). The hydraulics of open channel flow: An introduction Colorado Water Resources Research Institute (1996).Irrigation Water Conservation: Opportunities and Limitations in Colorado A report of the Agricultural Water Conservation Task Force. Daniil E.I., Michas S.N. and Lazaridis L.S. (2005). Hydrologic modeling for the determination of design discharges in ungauged basins. Early, A.C., Eckert, J.B., Freeman, D.M., Kemper, W.D., Lowdermilk, M.K., Radosevich, G.E., Skogerboe, G.V.(1976). Institutional Framework for Improved on-Farm Water Management in Pakistan. Colorado State University, Fort Collins, Colorado (Special Technical Report, Water Management Research Project). Evans O. Robert, Kerry A. Harrison, James E. Hook, Charles V. Privette, William I. Irrigation Conservation Practices, Appropriate for the Southeastern United States.
11 FAO (1789). Water for agriculture. Segars, W. Bryan Smith, Daniel L. Thomas, Anthony W. Tyson,1998. Irrigation Conservation Practices Appropriate for the Southeastern United States. Hargreaves and Merkley, 2004.Irrigation Fundamentals. Hussain, I., Perera, L.R. (2004). Improving Agricultural Productivity for Poverty Alleviation through Integrated Service Provision with Public-Private Sector Partnerships: Examples and Issues. International Water Management Institute, Colombo, Sri Lanka (Working paper 66). MINAGRI (2003). Groupement HYDROPLAN Ingénieur GmbH-S.H.E.R Ingénieur-conseils s.a, Schéma Directeur d'Aménagement des Marais, de Protection des Bassins Versants et de la Conservation des Sols. MINIPLAN (2002). Recensement Général de la Population et de l’Habitat. Rientjes, 2006. Modeling in Hydrology. Savenije H.H.G and de Laat P.J.M (2002).Lecture notes of Hydrology. Skogerboe V. Gaylord and Merkley P.Gary (1996). Irrigation Maintenance and Operation. Learning Process. Smith D.H., Kathleen Klein, Richard Bartholomay, Isreal Broner,G.E. Cardon, W.M. Frasier, Rod Kuharich, D.C. Lile, Mike Gross, Dan Parker, Hal Simpson, and Eric Wilkinson. Completion (1996). Irrigation Water Conservation: Opportunities And Limitations In Colorado-A Report Of The Agricultural Water Conservation Task Force. Texas water Development Board (2004). Agricultural Water Conservation Practices. Thomas W. Ley (2003). Surface Irrigation Systems.
12
Figures
Figure 1. Location of Migina in Rwanda and the Survey Area in Migina Catchment
13
Average rainfall per months calculated in 25 years 250.0
Rainfall (m m )
200.0
150.0
100.0
50.0
0.0 Jan
Feb
March
Apl
May
June
July
Aug
Sept
Oct
Nov
Dec
Months
Figure 2. Average rainfall of a reference year calculated basing on rainfall records in 25 years
Assesment of Operation of Rwasave Reservoir 90
Volume (*10^3 m^3)
80 70 60
Irrigation Requirements
50 Assessmet of Inflow&Storage in The Reservoir
40 30 20 10 0 may
jun
july
aug
sept
oct
nov
dec
jan
feb
mar
apr
Months From May To May
Figure 3. Monthly evolution in Water Storage of Rwasave Reservoir
may
14
Tables Table 1. Main characteristics of Migina catchment Catchment
Surface area (km2)
Perimeter (km)
Compacity coefficient
Slopes(%)
Flood Runoff coefficient (%)
Mean runoff coefficient (%)
Migina Total Catchment
214,23
79,24
1,52
30
8-12
Subcatchment a
3,14
6,73
1,06
30
8-12
Subcatchment b
3,39
7,33
1,11
30
8-12
Subcatchment c
37,50
27,10
1,24
30
8-12
Subcatchment d
2,67
7,05
1,21
30
8-12
Subcatchment e
4,56
9,06
1,19
30
8-12
Subcatchment f
44,20
29,73
1,25
30
8-12
Subcatchment g
4,29
8,92
1,21
30
8-12
Subcatchment h
3,76
7,89
1,14
30
8-12
Subcatchment i
5,97
10,48
1,20
30
8-12
Subcatchment j
37,51
31,74
1,45
30
8-12
Subcatchment k
11,18
15,14
1,27
Long. = 2 Trans. > 30 Long. = 3 Trans. > 20 Long. = 2 Trans. > 20 Long. = 4 Trans. > 30 Long. = 1 Trans. > 20 Long. = 1 Trans. > 20 Long. = 2 Trans. > 30 Long. = 3 Trans. > 30 Long. = 5 Trans. > 30 Long. = 3 Trans. > 30 Long. = 4 Trans. > 30 Long. = 1 Trans. = 20
30
8-12
Trans: Transversal slope Long: Longitudinal slope
Table 2.: Rainfall intensity at Butare rain gauge station Duration (min) 15
By Season
By year
56.8
66.0
30
45.4
45
By 2 years
15 years
10 years
75.2
87.2
96.4
53.4
61.2
71.6
79.4
34.9
41.3
47.7
56.3
62.5
60
29.2
34.8
40.4
47.8
53.4
75
23.6
28.2
32.7
38.8
43.4
90
20.2
24.3
28.3
33.5
37.6
15
Table 3. Maximum discharges (m3/s) calculated by using ORSTOM method Subcatchment Migina c f j k
tc 10 25 10 25 10 25 10 25 10 25
H 0.0797 0.0895 0.0797 0.0895 0.0797 0.0895 0.0797 0.0895 0.0797 0.0895
a 0.75 0.75 0.82 0.82 0.81 0.81 0.82 0.82 0.86 0.86
A
Vp 12805598 14380189 2450775 2752125 2853419 3204279 2451429 2752859 755300 860525
214230000 214230000 37500000 37500000 44200000 44200000 37510000 37510000 11180000 11180000
Kr 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
Vr 3841679 4314057 735233 825638 856026 961284 735429 825858 226590 258158
TB 36000 36000 25200 25200 25200 25200 25200 25200 14400 14400
M 106.7 119.8 29.2 32.8 34.0 38.1 29.2 32.8 15.7 17.9
K 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5
Qmax 266.8 299.6 72.9 81.9 84.9 95.4 73.0 81.9 39.3 44.8
Table 4. Maximum discharges (m3/s) calculated by using Rational method Subcatchment
Tr (years)
a b d e g h i
L(m)
10 10 10 10 10 10 10
Mean Alt(m) 1670 2130 2340 3150 3340 2430 4170
H(m)
1750 1750 1675 1675 1675 1700 1675
S(m/m)
50 42 40 45 100 122 113
Tc(min)
0.03 0.02 0.02 0.01 0.03 0.05 0.03
23 32 37 49 39 25 48
S. Area (km2) 3.14 3.39 2.67 4.56 4.29 3.76 5.97
i(m/hr)
C
87 77 72 60 69 85 61
Qdes (m3/s) 0.3 0.3 0.3 0.3 0.3 0.3 0.3
22.9 21.8 15.9 22.8 24.8 26.7 30.2
Table 5: Main emitters or drains designed with trapezoidal cross sections Sb. C Sb. Ca Sb. Cb Sb. Cc Sb. Cd S.b Ce Sb. Cf Sb. Cg
QMax (m3/ s) 22.9
h (m) 1.20
1.50
21.8
1.00
72.9
H (m)
K (s/m1/3)
VDes (m/s)
1.04
n (m1/3 /s) 0.03
30.03
4.37
22.9
4.46
0.89
0.03
30.03
4.80
21.4
7.04
9.77
1.39
0.03
30.03
7.48
73.1
0.01
5.44
5.20
0.96
0.03
30.03
2.91
15.1
0.33
0.01
5.64
6.61
1.17
0.03
30.03
3.34
22.1
6.40
0.33
0.02
8.44
1.68
0.03
30.03
6.00
84.8
3.00
0.33
0.03
5.04
14.1 3 4.85
0.96
0.03
30.03
5.07
24.6
B (m)
m (n.u)
S (n.u)
P (m)
A (m2)
3.00
0.33
0.02
5.04
5.25
1.30
3.00
0.33
0.03
5.04
1.45
1.75
5.00
0.33
0.04
15.9
1.05
1.35
3.40
0.33
22.8
1.30
1.60
3.60
84.9
1.70
2.00
24.8
1.10
1.40
R (m)
QDes (m3/s)
16 Sb. Ch Sb. Ci Sb. Cj Sb. C k
26.7
1.00
1.30
2.90
0.33
0.05
4.94
4.33
0.88
0.03
30.03
6.15
26.7
30.2
1.15
1.45
3.50
0.33
0.03
5.54
5.78
1.04
0.03
30.03
5.35
30.9
73.0
1.50
1.80
4.75
0.33
0.04
6.79
9.63
1.42
0.03
30.03
7.59
73.1
39.9
1.55
1.85
5.00
0.33
0.01
7.04
10.3 9
1.48
0.03
30.03
3.90
40.5
Sb.C i: Subcatchment i; Qmax: Maximum Discharge; h: Normal water level in the canal; H: Total height of the canal (including the free board of the canal); B: Base of the canal; m: Cotan θ = side inclination coefficient of the canal; P: Wetted Perimeter of the canal; A: Wetted Cross Section Area of the canal; R: Hydraulic Radius; n: Roughness Coefficient of the canal; K: Manning Coefficient; VDes: Designed Velocity; QDes: Designed Discharge.
Table 6. Crop water Coefficients (Kc) Rice 150
Rice120
Kc Kc ini 1,05 1,05 Kc mid 1,2 1,2 Kc end 0,6 0,6 Phase duration (in days) Init.(Lini) 30 20 Dev.(Ldev) 30 20 Mid(Lmid) 60 50 Late(Llate) 30 30 Cumulative phase duration (in days) Init.(Lini) 30 20 Dev.(Ldev) 60 40 Mid (Lmid) 120 90 Late (Llate) 150 120 In: Initial Phase;Mid: Middle Phase; Dev: Development Phase:
Maize 125
Beans 110
Potatoes13 0
Sorghu m 125
Aubergine
0,7 1,2 0,35
0,4 1,2 0,35
0,5 1,15 0,75
0,7 1,1 0,55
1,05 0,9 0,7
20 35 40 30
20 30 40 20
25 30 45 30
20 35 40 30
30 40 40 20
20 55 95 125
20 50 90 110
25 55 100 130
20 55 95 125
30 70 110 130
17
Table 7. Monthly crop water coefficients (Kc) Month
day 30
Rice 150 1,05
Rice 120 1,06
Maize 125 0,73
Beans 110 0,45
Potatoes 130 0,51
Sorghum 125 0,72
1
Aubergine 1,05
2
60
1,13
1,19
1,06
1,03
0,93
0,99
0,99
3
90
1,20
1,20
1,20
1,20
1,15
1,10
0,91
4
120
1,20
0,89
0,89
0,50
1,06
0,90
0,88
5
150
0,89
0,07
0,00
0,27
0,10
0,25
Table 8: Composition of mixed-crops Denomination
Crops
Mixed 1
Beans
50 %
Peppers
30 %
Cabbages
10 %
Groundnut
10 %
Maize
50 %
Soya
30 %
Beans
10 %
Cabbages
10 %
Corn Ears
10 %
Irish potatoes
20 %
Gren Beans
20 %
Mixed 2
Mixed 3
Proportion
Cropping intensity 100 %
100 %
50 %
Total
250 %
Table 9. Farming calendar for double rice crop production Speculation Rice-rice
Area (ha)
Crop 7.5
Rice 120
7.5
Rice 120 Rice 120
7.5 7.5 TOTAL
15.0
Rice 120
sep t
oct
nov
dec
ja n
feb
mar
april
may
jun
jully
aug
18
Table 10: Farming calendar for mixed-cropping Speculati on
Area (ha)
crop
Mixedcrop
360
Mixed1
360
Mixed2
360
Mixed3
TOTAL
sept
oct
nov
dec
jan
feb
mar
apr
may
jun
july
aug
360
Table 11. Assessment of operation of Rwasave reservoir Volume 10³ m³ Storable volume Losses by evaporation Irrigation water Requirement Outflow volume Assessment In/S
may 60 3 0
jun 0 3 1
july 0 4 15
aug 0 4 42
sept 16 4 0
oct 67 3 0
nov 78 3 0
dec 64 3 0
jan 58 3 0
feb 63 3 0
mar 57 3 0
apr 94 2 0
may 60 3 0
3 85
4 81
19 62
46 16
4 29
3 85
3 85
3 85
3 85
3 85
3 85
2 85
3 85
