Groundwater and surface water interactions in flat lands: the importance of ecological and flow regulation perspectives

Recharge in arid zones has been studied thoroughly due to the scarcity of groundwater that is available for extraction. However, the issue of depressed groundwater levels in sub-humid areas is mainly reflected by the contribution of the base flow to a watercourse; this contribution constitutes a very important alteration of the ecological conditions of a watercourse, including its substrate and surroundings. Continuous groundwater records from 2007 to 2014 for six wells located within the Del Azul Creek basin were analyzed. The recharge was calculated using the water table fluctuation method. The relationship between the groundwater level in each well and the base flow through a section of the creek was analyzed on a monthly basis to obtain a quadratic equation. The ecological flow of the stream was also determined, using the 7-day minimum flow method. Due that the base flow variations can strongly affect the ecological quality of this type of basin, with vertical flows more important than horizontal flows, the results are a contribution for water resource management practices in the areas of influence of surface water bodies. Groundwater mean monthly levels in wells located in the lower area of the basin, showed high adjustment coefficients for the quadratic equations that relate these levels to the base flow. These equations are good tools for decision makers regarding land use planning. Because our interest is low-flows, an equation that relates mean monthly base flow versus groundwater levels during the summer months are adjusted.