An Ecologically-Sustainable Surface Water Withdrawal Framework For Cropland Irrigation-A case study in Alabama
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Agricultural production in the State of Alabama, USA, mostly depends on natural rainfall. Because of this and also because of low and uncertain precipitation levels during growing seasons, agricultural production in Alabama is high vulnerable, especially during drought years. On the contrary, Alabama receives plenty of rain during winter months. Recently, the state agencies, researchers, and extension personnel in Alabama have been evaluating the feasibility of surface water withdrawal from stream during winter months and storing it for irrigation use in the growing period. A modeling study using the SWAT (Soil and Water Assessment Tool) model was completed for a Southwest Alabama watershed to estimate the quantity of water that could be withdrawn in an ecologically-sustainable manner from streams during winter high flow periods. The model was calibrated and validated separately using base flow, surface runoff, and total stream flow. The streamflows generated by the model at several locations within the watershed were then used to examine how much water can be withdrawn from streams of various orders (1st, 2nd and 3rd order) while satisfying the criteria for ecologically-sustainable stream flows. Although there was a considerable year-to-year variability in the amount of water that can be withdrawn, a sixteen year average simulation showed that 1st, 2nd, and 3rd order streams can irrigate about 11.6 %, 10.3%, and 10.6% of their drainage areas, respectively, per year. The percentage of drainage area that could be irrigated was found to be not a function of the order of the stream.