PLANNING OF AGRICULTURAL GROUNDWATER DEVELOPMENT FOR DROUGHT MITIGATION

Abstract

The present study addresses the problem of planning cropping pattern in normal hydrological years for drought mitigation through groundwater development. It has been observed that during drought, the irrigation requirement is mostly fulfilled through groundwater development. In the absence of adequate Static storage at the commencement of a drought, the water table decline during the drought may result in severe depletion of the Static storage that may jeopardize the well functionality. Further the depleted Static storage may not recover to the pre-drought level before the onset of next drought. The present simulation-optimization model aims arriving at such optimal cropping pattern that ensures adequate pre-drought Static storage - a prerequisite for the droughteffectiveness of groundwater development. The optimal cropping pattern apart from maximizing the returns from the agricultural activity ensures that the depleted Static storage at the end of drought is adequate for the well functionality. Further, it is ensured that depleted Static storage recovers before the onset of next expected drought. The composite groundwater flow model simulates the minimum water table elevation reached at the end of drought period and its recovery period during normal hydrologic years. The two state variables viz, minimum water table elevation (Hmj,) and recovery period of declined water table (TFR) are function of decision variables i.e. crop areas (A). The model is linked to an optimizer to generate optimized cropping pattern by constraining the two state variables stated above. The model proposed herein is applied to Narmada Command area, Gujrat, India. The study area is mostly prone to moderate drought. The application reveals that the groundwater development corresponding to the prevalent crop areas does not permit adequate Static storage for drought mitigation. As such, the optimized crop areas (smaller than the current areas) ensure that a Static storage corresponding to 15 m depth is available at the drought end. Further, it takes 9 years to recover back the depleted Static storage during normal hydrologic years.