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Charles Sturt University (2011)

Applying user pays principle to optimise salt drainage options in irrigation systems

Rana, Tariq

Titre : Applying user pays principle to optimise salt drainage options in irrigation systems

Auteur : Rana, Tariq

Université de soutenance : Charles Sturt University

Grade : Doctor of Philosophy in Environmental Engineering & Management 2011

Résumé
Irrigation of agricultural lands in arid environments can improve food security and human wellbeing. Poorly managed irrigation practices can raise watertables under the soil surface inducing water logging and salinity. But the problem can be controlled by conjunctive management of surface and groundwater resources. Management of groundwater can be achievedthrough drainage schemes aimed at agro-ecological salinity management by lowering the shallow groundwater to help increase agricultural production and reduce ecological risks due to shallow watertables and soil salinity. The groundwater levels need to be lowered to scientifically determined agroecological limits through optimum operation of pumping wells by managingspatiotemporally varying groundwater dynamics. Groundwater systems canbe optimised if their behaviour is fully known and understood but a keydifficulty in optimisation is dealing with non-linear and non-unique spatiotemporal groundwater dynamics. Changing conditions (rainfall, floodingand irrigation practices) also necessitate a dynamic approach to operatingthe drainage scheme. Some of the pumping wells can prove to be ineffective while others may be drawing more water than their desired designdischarges. Such problems can be optimised using genetic algorithms (GA)aimed at finding near optimal solutions to highly non-linear optimization problems. The major advantages of these algorithms are their broad applicability, flexibility and their ability to find optimal or near optimal solutions with relatively modest computational requirements.This study presents the development of a surface-ground water interaction regional model using MODFLOW and GA based spatio-temporal optimisation of the pumping operation of a subsurface drainage scheme using a spatially zoomed drainage scheme level surface-ground waterinteraction model to achieve a similar or better than on-going level of service both in space and time domains.Paddock-scale groundwaterre charge was estimated using the SWAGMAN Farm model. The Murray Irrigation Area and the Wakool Tullakool Subsurface Drainage Scheme(WTSSDS), from New South Wales, Australia is used as a case study to illustrate the modelling process. The model results are currently being used by the irrigation company to plan the cost-effective operation of thepumping wells to control water logging and salinisation in the area.One of the key operational issues for this scheme is rational sharing of costsand benefits between the primary and secondary beneficiaries. The total capital cost of scheme was around $32 million with grants provided by the Commonwealth Government, under the Federal Water ResourcesAssistance programme, the NSW Government provided the balance. The operation and maintenance costs are collaboratively met by the shareholderswith a cost sharing arrangement with the NSW State Government due to the salt interception value to the Murray River. This study also develops a framework to rationalise salt drainage cost sharing options in irrigationsystems by applying the user pays principle to mitigate waterlogging and salinity impacts. Integrated hydrological, economic, and institutional models are used to convert spatial quantification of groundwater draw down to level of service provided to individual farms and saline flow interception to the surrounding streams for appropriate cost sharing of salinity managementresponsibilities among farmers and the regional water regulation bodies.

Mots clés : Groundwater - Management ; Groundwater - Economic aspects.

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Page publiée le 7 novembre 2011, mise à jour le 3 juillet 2017