Data Collection and Processing: A significant amount of data that have been collected to fulfil the requirement of the study activities include rainfall, evaporation, groundwater level, river water level and discharge, aquifer test and bore logs, seepage and percolation. These data were thoroughly checked following the IWM’s standard quality checking procedure. Details on the methodology adopted for quality checking can be found in IWM Data Processing Manual (IWM, 2004).
Assessment of Water Requirement:The total water requirement for the study area is the sum of the water requirement for irrigation, domestic and municipal water use. Upazila wise irrigation water requirement is estimated based on the present crop coverage within the Upazila while domestic & municipal water requirement is estimated based on the present and future projected population of the Upazila and per capita water demand as suggested in NWMP (WARPO, 2004). Irrigation water requirement has been estimated for the major crops with staggered plantation. The idea is to find the optimal planting time when water requirement is minimum. Potential evapotranspiration has been calculated using Penman-Montieth method. Effective monthly rainfall has been taken as the 80% of monthly total rainfall. Percolation rate has been taken from field measurements, which varies from 2 mm/day to 4 mm/day. The maximum unit scheme water requirement corresponding to critical month for each crop is computed with an overall efficiency of 90% as most of irrigation in the study area is based on groundwater through irrigation wells of small scheme, mostly of 2.0 cusec capacity. The CROPWAT version 5.7 of FAO has been used to compute irrigation water requirement.
Development of Models: The main purpose of model study is to assess and evaluate the overall water resources of the study area with the view to bring potential areas under irrigation coverage for increasing agricultural production through optimum utilization of available water resources. To assess the water resources availability in the study area, integrated MIKE 11-MIKE SHE modelling system has been adopted. The modelling system is physically based and distributed and capable of addressing the land water ecosystem in an integrated manner. The model enables better understanding of the river-aquifer interaction, as well as, providing a tool that can be used to manage the water resources in the best possible way considering the relative contribution of the components on the water balance in the area. The models developed are based on MIKE-11 for surface water model and MIKE-SHE for groundwater model. Both the models have been coupled and run dynamically.