Modeling approaches to quantify the water balance in groundwater-dominant irrigation systems: an example of Rechna Doab, Pakistan
2002
Khan, S. | Ullah, K. | Christen, E. | Nafees, H.M.
Irrigated agriculture in alluvial basins is characterized by high seepage losses from rivers, channels, and irrigated fields to the aquifer systems. Water accounting at the farm or management unit level tends to underestimate the productive use of water since losses from the supply system can be reused for irrigation through downstream groundwater pumping. However, pumping can mobilize poor-quality groundwater and can cause an overall loss of good-quality water supplies. Increased grounwater pumping also increases seepage losses from irrigation channels and watercourses. This situation required an understanding of spatial and temporal variation of surface-water and groundwater interactions and salt movements under variable scenarios of surface-water availability. This paper describes details of hydrological studies in the Rechna Doab basin, Punjab, Pakistan. The basin has 3 million ha, of which 2.3 million ha are cultivated land with rice, cotton, and fodder crops dominating in the summer and wheat and fodder in the winter. A top-down nodal network was developed to determine the irrigation water balance for individual administrative units. The spatial groundwater recharge estimates obtained from the nodal network were used to check the water balance estimates from a more distributed bottom-up approach. The bottom-up approach used a distributed dynamic model that simulated surface-water and groundwater interactions at the desired level of interest. The distributed nature of the surface-groundwater interaction model enabled a performance assessment of individual administrative units by taking into account downstream beneficial use and quality variation of lost surface water. This water and salt balance approach high-lighted the need for integrated management of surface water and groundwater from the administration unit to the basin level.
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