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Irrigation Matters Series No. 05/08

Assessment of Evaporation Losses and Evaporation Mitigation Technologies for On Farm Water Storages across Australia Craig Baillie October 2008

BETTER IRRIGATIO N

BETTER ENVIRONMENT

BETTER FUTURE

Assessment of Evaporation Losses and Evaporation Mitigation Technologies for On Farm Water Storages across Australia

Craig Baillie National Centre for Engineering in Agriculture

CRC for Irrigation Futures

CRC for Irrigation Futures Irrigation Matters Series No. 05/08 October 2008 CRC for Irrigation Futures

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CRC IF Copyright Statement © 2008 IF Technologies Pty Ltd. This work is copyright. It may be reproduced subject to the inclusion of an acknowledgement of the source.

Important Disclaimer The Cooperative Research Centre for Irrigation Futures advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, the Cooperative Research Centre for Irrigation Futures (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it.

Acknowledgements This report acknowledges the contribution of the following people for assistance in the collection of data, direction on current and previous work and advice on systems currently in place across the various states to account for farm dams.

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Queensland Department of Natural Resources and Water (NRW): Gerry Bisshop, Jasmine Muir, Tim Danaher, Mark Ely, Tony Horton

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NSW Department of Natural Resources (DNR): Richard Hicks, Phil Moss,

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Environment ACT: Peter Liston

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Sinclair Knight Mertz (SKM): Rory Nathan, Katherine Williams

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Tasmania Department of Primary Industries and Water (DPIW): Robert Phillips

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South Australia Department of Water, Land and Biodiversity Conservation (DWLBC): Craig Walker, Shaun Dwyer, Bruce Murdoch

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Western Australia Department of Water (DoW): Robert Donahue

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Northern Territory Department of Natural Resources, Environment & the Arts. (NRETA): Ian Lancaster

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FSA Consulting: Peter Watts, Ainsley Smith


Executive Summary Australian agriculture is highly dependant on farm dams. Storage sizes range from a few megalitres (ML) for stock and domestic supplies to larger dams used for commercial irrigation. Conservative estimates suggest that in excess of 8 000 000 ML is stored in farm dams (i.e., 9% of total stored water) and that there are more than 2 million farms dams across Australia (Australian Water Association, 2006). Access to data on farm dams across Australia to support this estimate is relatively difficult to obtain. To account for farm dam numbers and volumes across Australia there are broadly two data sources and methods for identifying farm dams. These sources include data that is routinely collected due to licensing requirements and data obtained through remote sensing, which in the past has been specifically employed to assess the impact of farm dams on natural resources. To determine the impact of farms dams there is a need to be able to determine the location and size of farms dams. Recent changes to legislation in various states has tightened the licensing of farm dams and therefore resulted in potentially better records. In many cases however there is still sufficient exemption from licensing, leading to under detection, which has a significant impact on natural resources. In some catchments of southern Australia overland flow diversion due to farm dams is greater than 20% (Schreider and Jakeman 1999). A significant proportion of this is through small dams i.e. ~ 5 ML that don’t necessarily require a licence. Apart from the diversion of overland flows evaporation losses from farm dams can exceed 40% of the storage volume. Although it is generally acknowledged that the total evaporation losses from farm dams across Australia is significant, accounting for these losses is difficult given the large discrepancy between national estimates and the information collated from various state agencies and territories. To illustrate this point less than 50 % of the estimated number of farm dams can be accounted for. Similarly only 60% of the estimated volume of farm dams can be accounted for. Satellite imagery provides the best means of fully accounting for farm dams and can be used to determine the growth, location and surface area of farm dams. In particular these techniques not only provide a snap shot of farm dam development but can also utilise historical imagery to determine changes in farm dams spatially over time. Whilst the data collated to date cannot fully account for the storages estimated nationally the data provides a useful sample in which the characteristics of storage sizes can be determined for each state. These characteristics were extrapolated to a total storage volume of 8 000 GL (i.e. national estimate) to determine the potential losses from on farm storages and the application of Evaporation Mitigation Technology (EMT). It was estimated that evaporation losses from on farm storages was 1 320 000 ML and as high as 2 880 000 ML. The employment of various EMT products could reduce these losses by 480 000 to 700 000 ML depending on the performance of chemical barriers i.e. monolayers. Given that the most significant impact on evaporation mitigation was due to monolayers i.e. potentially 350 000 ML and that performance of these products are highly variable, future research and development needs to focus on this area if potential evaporation savings are to be realised.


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Contents Executive Summary...................................................................................................... ii Acknowledgements ...................................................................................................... ii 1 Introduction ........................................................................................................... 1 2 Systems for Accounting of Storage Dams by State Agencies ......................... 2 2.1 Queensland ..................................................................................................... 2 2.2 New South Wales ........................................................................................... 3 2.3 ACT ................................................................................................................. 3 2.4 Victoria ............................................................................................................ 4 2.5 Tasmania ........................................................................................................ 4 2.6 South Australia ................................................................................................ 4 2.7 Western Australia ............................................................................................ 5 2.8 Northern Territory ............................................................................................ 5 3 Technology Used for Identifying and Quantifying Storage Dams ................... 7 3.1 Overview of Technologies ............................................................................... 7 3.2 Application of Technologies by State Agencies .............................................. 9 4 Collation of Available Storage Size Classes .................................................... 12 4.1 Queensland ................................................................................................... 13 4.2 New South Wales ......................................................................................... 15 4.3 ACT ............................................................................................................... 15 4.4 Victoria .......................................................................................................... 16 4.5 Tasmania ...................................................................................................... 17 4.6 South Australia .............................................................................................. 19 4.7 Western Australia .......................................................................................... 20 4.8 Northern Territory .......................................................................................... 22 4.9 All Data ......................................................................................................... 22 5 Determination of Potential Evaporation Losses .............................................. 25 6 Assessment of Market Potential for Evaporation Mitigation Technologies (EMT) ............................................................................................................................ 27 6.1 Floating covers .............................................................................................. 27 6.2 Shade cloth ................................................................................................... 28 6.3 Chemical barriers .......................................................................................... 28 6.4 Market potential of products .......................................................................... 29 6.5 Case Studies Examples of EMT Products .................................................... 31 7 Conclusion / Recommendations ....................................................................... 33 8 References .......................................................................................................... 35 Appendix A: Determination of Surface Area – Volume Relationship for Farm Dams ............................................................................................................................ 37

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List of Figures Figure 1 Aerial photography identifying farm dams (source SKM) .......................................... 7 Figure 2 Example of a digital elevation model of a farm dam ................................................. 8 Figure 3 Satellite image detailing farm dam (source: SKM) .................................................... 8 Figure 4 Volume of water stored in various class sizes (Queensland) ................................. 14 Figure 5 Number of storages relative to various class sizes (Queensland) .......................... 15 Figure 6 Volume of water stored in various class sizes (Victoria) ......................................... 17 Figure 7 Number of storages relative to various class sizes (Victoria) .................................. 17 Figure 8 Volume of water stored in various class sizes (Tasmania)...................................... 18 Figure 9 Number of storages relative to various class sizes (Tasmania) .............................. 19 Figure 10 Volume of water stored in various class sizes (South Australia) ........................... 20 Figure 11 Number of storages relative to various class sizes (South Australia).................... 20 Figure 12 Volume of water stored in various class sizes (Western Australia) ....................... 21 Figure 13 Number of storages relative to various class sizes (South Australia).................... 22 Figure 14 Volume of water stored in various class sizes (all data) ........................................ 23 Figure 15 Number of storages relative to various class sizes (all data) ................................ 23 Figure 16 Distribution of Farm Dams across Australia .......................................................... 24 Figure 17 EMT - Floating cover ............................................................................................. 27 Figure 18 EMT - Shade cloth ................................................................................................. 28 Figure 19 EMT - Chemical barrier ......................................................................................... 29 Figure 20 Percentage of water in storages ............................................................................ 30 Figure 21 Potential Water Savings from EMTs...................................................................... 30 Figure 22 Volume to Surface Area Relationship (Queensland Overland Catchments) ......... 37 Figure 23 Surface Area to Volume Relationship (Queensland Overland Catchments) ......... 37 Figure 24 Surface Area to Volume Relationship (Queensland Watercourses)...................... 38 Figure 25 Surface Area to Volume Relationship (Queensland Watercourses)...................... 38 Figure 26 Surface Area to Volume Relationship (Tasmania) ................................................ 39 Figure 27 Surface Area to Volume Relationship (Tasmania) ................................................ 39 Figure 28 Surface Area to Volume Relationship (South Australia) ........................................ 40 Figure 29 Surface Area to Volume Relationship (South Australia) ........................................ 40 Figure 30 Surface Area to Volume Relationship (Western Australia) .................................... 41 Figure 31 Surface Area to Volume Relationship (Western Australia) .................................... 41

List of Tables Table 1 Volume in Storages (ML) .......................................................................................... 12 Table 2 Number of Storages.................................................................................................. 12 Table 3 Storage losses across Australia (ML) ....................................................................... 26 Table 4 Case Study Examples of Water Savings from EMTs ............................................... 32


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1 Introduction Australian agriculture is highly dependant on farm dams. Storage sizes range from a few megalitres (ML) for stock and domestic supplies to larger dams used for commercial irrigation. Conservative estimates suggest that in excess of 8 000 000 ML is stored in farm dams (i.e., 9% of total stored water) and that there are more than 2 million farms dams across Australia (Australian Water Association, 2006). Despite these estimates there is no complete record of farm dam numbers, spatial distribution or sizes making it difficult to assess the potential impacts. In some catchments of southern Australia overland flow diversion due to unregistered farm dams is greater than 20% (Schreider and Jakeman 1999). In addition evaporation losses from farm dams can exceed 40% of the storage volume. It is generally accepted that evaporation is one of the larges losses facing farmers and water authorities and that evaporation from farm dams in Australia is regarded as one of the few areas where there are real water savings to be made (Watts 2005). Without any record of storage numbers and sizes it is difficult to define the true benefits of technologies for reducing evaporation losses and to target the development and application of these technologies. In response the aim of this report was to: •

Collate available information on farm dam numbers and sizes;

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Identify processes that could be employed to account for on farm storages across Australia;

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Assess the potential evaporation losses from farm dams across Australia;

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Determine relative storage sizes and their significance to the total water stored on farm;

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Identify the potential application of various Evaporation Mitigation Technologies (EMTs); and

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Determine potential evaporation savings through the adoption of evaporation mitigation technologies i.e. EMTs.


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2 Systems for Accounting of Storage Dams by State Agencies There are various systems is place for accounting of farm dams in each of the states. The mechanism for recording farm dam information includes a licence to take water from a water course, licence to take water from over land flow in declared catchments, licence to construct works and various local permits. Generally in stream dams require licensing while off stream dams in comparison are poorly regulated. Although most jurisdictions hold data on licensed dams there is relatively little information on unlicensed farm dams. Recent water reforms in each of the states has tightened the requirements for licensing farm dams however there are many cases where storages haven’t been recorded or are less than the lower thresholds required for licensing. The best example of this occurs in Victoria, South Australia and Western Australia. In these states a significant number of farms dams are less that 2 Ha in surface area while representing a significant volume (40%) of water stored on farm. Prior to a relatively comprehensive study on farm dams in Victoria, 13% of the total capacity of farms dams could be accounted by licensed storages. In most states farm dam licensing information is supported through electronic data bases. Whilst this data set is not a complete record of the number of farm dams in place it does provide a sample to classify storage sizes. Notably the Northern Territory and the ACT are exceptions where no data could be sourced. Data obtained for NSW was limited to storage location (i.e. latitude and longitude).

2.1 Queensland The requirement for recording information on farm dams in Queensland varies across the state. In broad terms information relating to farm dams is collected through licensing to take or interfere with water; licensing a referable structure and various permits required to construct works and build infrastructure. Generally the licensing requirements to take or interfere with water depend on whether the catchment has regulated or non regulated overland flow. In all cases the storage of water in excavations that are within or connected to a water course requires a licence. For catchments that have regulated overland flow the requirement for licensing farm dams vary and depends on the specific catchment’s Water Resource Plan. In some catchments storages are limited to 5ML while in other areas storages are limited to 250ML before prior approval and licensing is required. Farm dams that are used to contain drainage water to conform to best management practice are exempt (i.e. cotton industry). In catchments with non regulated overland flow, water storages / farm dams may be captured as a referable structure. Generally a dam is referable if a population is at risk

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due to dam failure. A referable dam is determined by a failure impact rating which is dependant on the outcomes of a failure impact assessment. Failure impact assessments are required for dams that are 8 m high and more than 500 ML or 8 m high, more than 250 ML and with a catchment area 3 times the dam’s maximum surface area at full supply level. Information on the states water licenses is collected on the Water Entitlements Registration Database (WERD). The system records details about the prospective or existing licensee or permit holder; the identifier of land which is attached to the authority; the identifier of the land where the works are located; the location and source of the water supply; and the technical information which physically describes the existing or proposed works.

2.2 New South Wales There are a number of categories in which farm dams require licensing in NSW. The total capacity of all dams on a property exceeding the Harvestable Right Dam Capacity (MHRDC), which is greater than 10% of the average regional rainfall runoff from the property requires a licence. Licences are not required for farm dams built before 1999 providing these dams are used for stock and domestic watering purposes. Small dams up to 1 ML in size where the property was approved for subdivision before January 1 1999 are also exempt from licensing providing the MHRDC is less than 1 ML. Other exemptions occur for dams that are not used for irrigation or required by regulation to contain drainage water to conform to best management practice. Access to electronic data on farm dams in NSW was limited to storage location only.

2.3 ACT Apart from water used for stock or domestic purposes (including irrigation of domestic gardens less than 2 Hectares) both a licence to take water and a water allocation is required to use water for any purpose including the collection of overland flows. A land holder must first possess a water allocation to apply for a licence to take water (ACT Government 2006a). In addition a permit is required to construct or alter a dam, water storage or other water control structure, except for a dam less than 2 ML capacity and which is not on a waterway (ACT Government 2006b). The licensing authority responsible for issuing licences to take water and water allocations is Environment ACT. It is understood that the majority of water stored on farm is used for watering stock. Under legislative requirements these storages are not required to be licensed and therefore no electronic record of farm dams exist for the ACT (P. Liston, pers. comm., 2006) It is suspected that a significant amount of water is stored in farm dams and the impact includes large evaporative losses and reduction in overland flow.


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2.4 Victoria All farm dams built on water ways and where dams are used for irrigation or commercial purposes require a license. Licensing includes water extraction (take and use licence) or the construction of works associated with the extraction of water. In some instances operational licences will also be required to set certain operating conditions such as allowing flow to pass the dam at specific times of the year. Take and use licenses are required regardless of the dam being in a water way or not. For dams in place prior to recent changes in the Water Act (Victoria) registration licences were offered from a period of 1 July 2002 to 30 June 2003. Dams built in a water way require a construction licence while dams built off a water way are subject to 5 metres or higher and 50 ML capacity or larger or, 10 metres or higher and 20 ML capacity or larger or, 15 metres or higher, regardless of capacity. Other requirements for licensing might depend on local shire or council permits. In Victoria licensing authorities are responsible for regulating the construction of dams and the use of water. Licensing authorities include Goulburn-Murray Water, Southern Rural Water, Sunraysia Water Authority, Wimmera Mallee Water and Melbourne Water. For new dams the licensing authority will refer the application to Department of Natural Resources and Environment, local government and catchment management authorities before it is approved.

2.5 Tasmania In Tasmania access to water via farm dams is controlled by licensing diversions and the issuing of a water allocation. The dam approval process is regulated by the water management Act 1999. Water taken from a river, stream or stored in a farm dam for irrigation and commercial purposes requires a licence which can be obtained from the Department of Primary Industries and Water. A water allocation must be obtained by establishing a right or transferring water from another licence. Under the water management Act 1999 a dam permit is also required for all dams except a dam that is not on a water course and that holds less than 1 ML of water or a dam constructed from the primary purpose of storing waste. Information on the State’s water licenses, water allocations and dam permits are stored on the Water Information Management System (WIMS) database. Specific details on the database include clients, purpose and amount of water allocated and the size and capacity of dams.

2.6 South Australia The mechanisms for licensing farm dams in South Australia include development approval under the Development Act 1993 and a permit under the Water Resources Act 1997 to assess the impact that the storage will have on water flows and yield

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(DWLBC, 1997). Development approval is required for dams with a wall height greater than 3 m or a capacity greater than 5 ML. The principles in which farm dam permit applications are assessed depend on for example the requirement for by pass flow, the construction of the storage off stream, non erosive and / or ecological sensitive areas. The licensing authority for both development approval and permit of use is the Department of Water, Land and Biodiversity Conservation (Resource Management Division)

2.7 Western Australia The licensing of farm dams in WA is required for all dams that are located in a proclaimed catchment area. Generally licenses aren’t required outside of a prescribed area or for stock and domestic supplies. Presently not all catchments are proclaimed under the Rights in Water and Irrigation Act 1914, but this is constantly under review as demand for water increases or environmental pressures increase. In a proclaimed catchment a permit is required to 'Interfere with Bed and Banks' of a watercourse, i.e. build a dam or riffle on a stream, soak or spring. In an unproclaimed catchment a permit is only required if the watercourse is within a reserve or unallocated crown land, ie freehold land is exempt, but the Department has the power to direct specific actions if the structure is likely to damage the water course or interfere with the rights of existing users. In a proclaimed area where a watercourse is within or contiguous to a property, the owner may claim riparian rights to take water for domestic use, stock watering and the irrigation of up to 0.2ha for non-commercial purposes. Where a property owner has access to a watercourse via a public road or reserve he can claim 'Other Rights' to take the water for the same purposes as for riparian use without a licence. All other usage, ie commercial, requires a Surface Water Licence. In non proclaimed areas the same riparian and 'Other' rights apply but water may also be taken for any other purpose without a licence as long as this does not interfere with the rights of other users and providing the flow is not 'sensibly diminished' (R. Watson, pers. comm., 2006). Farm dam licensing information is collected on the Water Resources Licensing system (WRLS). The WRLS database holds information on individual dams such as dam wall height, storage capacity, usage and water allocation regime (Bonieka 2007).

2.8 Northern Territory The administration of water resources in the Northern Territory is under the NT Water Act. The requirements to licence farm dams in the Northern Territory is dependent on the size and location of the dam wall within the catchment. Broadly there is no requirement


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to licence dams which are either off stream or if the storage has a catchment less than 5 squared kilometres and a wall height less than 3 metres. In practice there is no significant use of surface water in the Northern Territory due to high evaporation rates, high soil porosity, and few suitable dam sites. Water for irrigation is preferably sourced from groundwater. In total there are 3 “large” dams that are licensed, only one of which is used for agricultural uses with the other two dams used for public water supply (I Lancaster, pers comm., 2007) and as a result there is no electronic register of farm dam licensing information.

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3 Technology Used for Identifying and Quantifying Storage Dams 3.1 Overview of Technologies To supplement licensing information numerous investigations have been conducted particularly in the Murray Darling Basin, Queensland, Victoria, South Australia and Western Australia to identify farm dams through remote sensing techniques. As discussed, there are a large number of small dams in these states which represent a significant proportion of the total water stored on farm. Of specific interest is the influence and impact that these storages ultimately have on natural resources. Generally in the past farm dams have been identified through aerial photography which is manually digitised and interpreted (heads up digitising). Variations of this include orthographically rectified digital imagery where some of the manual processes are eliminated by automatically identifying the water body from the contrast of the surrounding landscape and then manually outlined. Aerial photos provide high resolution imagery (30 cm pixels) and convenience where existing data sets occur.

Figure 1 Aerial photography identifying farm dams (source SKM)

In addition to the location and surface area of the storage, surface to volume relationships are derived from a sample of licensed information, ground reconnaissance, topographic maps or digital terrain models (DTMs) from sophisticated aerial survey techniques to approximate storage volumes. Sophisticated aerial techniques (Figure 2), otherwise known as active remote sensing, includes laser scanning (i.e. light detection and ranging, LIDAR).


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Figure 2 Example of a digital elevation model of a farm dam using LIDAR data (source SpatialVision).

Increasingly satellite imagery is being used to identify and trace the outline of farm dams automatically. This dramatically reduces the time and processing costs for identifying farm dams. Image resolution varies from 25 metre pixels to 2.4 metre pixels. Options include Landsat (25 m), Spot (5 m and 10 m), Ikonos (2.4 m) and Quickbird (2.4 m). Satellite images are multispectral (mostly 4 bands including red, green, blue and near infra red) which enables identification of water bodies from spectral analysis techniques. Depending on the satellite, the resolution of the multispectral image can be enhanced or “pan sharpened”. Quickbird images for example can be improved to 0.6 m resolution by using the higher resolution panchromatic (black and white) images also recorded by the satellite.

Figure 3 Satellite image detailing farm dam (source: SKM)

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3.2 Application of Technologies by State Agencies Queensland In Queensland for example state-wide water body coverage has been produced (by Queensland Department of Natural Resources and Water), that shows the spatial extent and location of all large dams. This coverage has been used in applications requiring the determination of water body existence and their persistence. Water bodies were automatically mapped using a time series of Landsat 5 & 7 images, ranging in date from 1986 to 2005, (typically winter imagery of 1988, 1991, 1993, 1995, 1997, and yearly from 1999 to 2005). Whilst the Landsat data provides a temporal record of storages, the spatial resolution is limited to dams larger that 0.25 hectares (25 m pixels). Additional attributes, including the name, primary use and owner/s of dams, have been incorporated into the final dataset, by matching features to point features from a database provided by Dam Safety (Department of Natural Resources and Water), where features were within 100 m of waterbodies derived from satellite imagery. Additionally features smaller than 1 875 m2 (a group of 3x25m pixels or less) have been excluded from the dataset, to meet the requirement of identifying large dams in Queensland. Smaller dams may be mapped in a future project. New South Wales A number of studies have recently been completed which has used satellite data to identify farm dams. This work has included a study on hillside dams conducted by Agrecon and a program of mapping farm dams in the Murray Darling Basin by Geoscience Australia. A similar process to that described for Queensland has been also conducted in NSW for change detection of vegetation. As a result of this work a wet layer of water bodies was compiled, which could be used to identify farm dams. NSW also has relatively high resolution (i.e. Spot 10 m) satellite coverage of the state which can be used to identify farm dam presence. Victoria Across Victoria the number and size of farm dams were determined using a combination of aerial photography and digital topographic information to identify the impact of farm dams on overland flow (Lett and Morden 2004). Identification of farm dams using aerial photography for sample catchments was used to adjust farm dam numbers and sizes from base topographic data to reflect the current level of development. The combination of methods was required as i) the base data set was up to 30 years old (1974 – 1991), ii) generally underestimated the number of small dam sizes and iii) either existing coverage of aerial photography was limited or cost prohibitive. The processing of aerial photography was partially automated. GIS software was used to identify water bodies based on colour and feature in contrast to the surrounding landscape and then manually outlined. Data was manually checked to qualify farm dams from water bodies. Once surface area information for farm dams was obtained dam volumes were derived from surface area to volume relationships. These


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relationships are specific to local regions and where determined from survey information and LIDAR analysis (Figure 2) South Australia In South Australia a number of catchments were studied to determine the impact of farm dams on overland flows (McMurray 2003, Savadamuthu 2002, Teoh 2002, Heneker 2003). Aerial photography was used to identify location and size of farm dams. The identification of farm dams included manually digitising (heads up digitising) the outline of farm dams from aerial photography and digitised ortho-rectified aerial photography. Information obtained from the aerial photos was verified by field surveys to also determine a surface area to volume relationship. Western Australia Recently high resolution Quickbird satellite imagery (2.4 m pixels) was used by Sinclair Knight Mertz (SKM) to identify farm dams in the south west of Western Australia (Williams, 2006) on behalf of the Department of Water (DoW). Using image analysis software a number of factors including spectral analysis of the satellite image was used to define the farm dam including water surface and the cleared banks (full supply level). In this study a comparison with manually interpreted aerial imagery netted similar results. E Cognition software was also used to further select various features i.e. white images near water could be used to determine the banks of the dam. This software was used to also derive the full supply levels of dams when they were less than full. Additional work was conducted by the (DoW) to develop a localised algorithm to convert surface area to storage volume. Murray Darling Basin Commission (MDBC) In late 2007 Geoscience Australia completed mapping of approximately half of the Murray Darling Basin using high resolution satellite imagery (2.5m SPOT5) to determine the growth, location and surface area of farm dams in the basin. This study not only provided a snap shot of farm dam development within the basin (2005) but also utilised historical moderate resolution LANDSAT imagery to qualify changes in farm dams spatially over time. The project attempted to undertake a complete census of farm dams within the study area as opposed to previous sampling techniques. The development of farm dams in the 10 years proceeding 2005 was identified to be 6% although this varied depending on location in the basin. The most significant increases occurred in Northern New South Wales and Queensland (i.e. 12 – 18%). The results of the study gave some insight into the types of monitoring that would be required to monitor farm dam development into the future. The results demonstrated the highly localised nature of dam development where dramatic increases have occurred within catchments. As a result the use of remote sensing needs to be balanced between high resolution and frequent coverage where significant change is likely to occur compared with more systematic monitoring of larger areas to detect changes that are not as predictable. Geoscience Australia (2008) suggested that operationally this may consist of a monitoring program that includes: annual 2.5 and 10 m coverage of intensive land

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uses, annual 10 m coverage over moderately intensive areas and more frequent coverage with reducing resolution such as seasonal coverage at 25 – 60m resolution imagery and weekly coverage at 250m – 1 km resolution.


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4 Collation of Available Storage Size Classes Available data from a range of sources was collated to classify storage sizes across Australia. This data included information from licensing databases i.e. Queensland, Tasmania and South Australia and other studies identifying farm dams from remote sensing techniques i.e. Victoria, South Australia and Western Australia. Data for the Northern Territory and the ACT was unavailable while data for NSW contained only location data. In the Northern Territory irrigation is predominantly from groundwater with small turkey nests (next to bores and less than 1 ML) for watering stock. Similarly, farm dams in the ACT are almost entirely for watering stock. In lieu of the data constraints outlined for NSW additional data was obtained from work undertaken by the MDBC and sourced from Webb, McKeown and Associates (2007) and Geoscience Australia (2008). This data was presented on a catchment basis and in some instances overlapped state boundaries. Data from the various sources mentioned, was collated and filtered to remove storages with a surface area greater than 100 hectares. It was assumed that storages with a surface area less than 100 hectares reflected the upper limit of farm dam sizes or alternatively the lower limit of commercial water supply storages. This indicated that the total storage capacity of farm dams is 4 252 550 ML (Table 1) while the total number of farm dams that could be account for was 735 607 (Table 2). Additional data on farm dams was obtained from the Australian Bureau of Statistics (ABS, 2006) and is compared to the data described above in Table 1. Table 1 Volume in Storages (ML) Storage Size (Ha) 0-2 2-5 5 - 10 10 - 25 25 - 100 > 100 unavailable Total ( 100 127 unavailable Total (