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Wageningen Universiteit (2005)

Decision support system for floodwater spreading site selection in Iran

Kheirkhah Zarkesh, Mirmasoud

Titre : Decision support system for floodwater spreading site selection in Iran

Auteur : Kheirkhah Zarkesh, Mirmasoud

Université de soutenance : Wageningen Universiteit

Grade : Doctor Thesis 2005

Résumé partiel
Most aquifers of semi-arid Iran suffer from over-exploitation of groundwater for irrigation. It is therefore important to augment the groundwater resource by artificial recharge, using flood waters that flow into salt lakes or in the sea. The recharge schemes consist generally of diversion of part of the flood discharges of ephemeral rivers in small to medium sized catchments onto infiltration basins. Apart from recharge of groundwater, supporting food production and drinking water supplies, the schemes have other benefits, such as mitigation of flood damages and ‘greening of the desert’. Many governments, including the one of Iran, place now much emphasis on increasing the number of floodwater spreading schemes. A large number of factors play a role in the selection of the most suitable sites for deciding on investment in a scheme. These factors pertain to earth science (geology, geomorphology, soils), to hydrology (runoff and sediment yield, infiltration and groundwater conditions) and to socio-economic aspects (irrigated agriculture, flood damage mitigation, environment, job creation and so on). Hence, the decision depends on criteria of diverse nature. This thesis deals with developing a Decision Support System (DSS) to assist decisions as to where the most suitable catchments and associated infiltration areas are and to work out options of types of schemes, which are adjusted to the characteristics of the selected infiltration area (the site available). After discussion of the bio-physical setting for flood spreading schemes in the Introduction (Chapter 1), attention is given to the selection of the desired approach for multi-criteria evaluation in Chapter 2. The Analytical Hierarchical Processes (AHP) approach was considered to be appropriate for the problem at hand and use was made of the spatial extension of this approach in a GIS environment, after structuring all the major criteria for a flood spreading scheme. Of key importance is of course the expected infiltration of flood water diverted. For such an a-priori estimate the effect of soil textures in a soil column on infiltration and percolation have to be made, as well as an estimate of the effects of sedimentation of clay and sand in a scheme, as well as effect of inundation depth and flooding frequency. One-dimensional soil modelling was done with the SWAP model, Chapter 3, using two pedo-transfer functions for the hydraulic parameters based on textures. It was found that for coarse textured soils there was reasonable agreement between functions used, but quite some differences were found for the soils containing clay and silt. As expected, recharge efficiency was positively affected by inundation depth and by rapid succession of inundations. Because simulation results differed, the recharge of the complex and large Sorkhehesar scheme was analysed, by developing a spreadsheet programme to work out depths, areas and duration of inundation, Chapter 4. It was found that the Mualem-van Genuchten transfer function was the most appropriate one.


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