Potential for groundwater recharge during floods: First-order estimates

Observed variations in water levels of aquifers located in arid and semi-arid areas around the world indicate that significant recharge may occur during flooding events that happen with a frequency of one in every decade or so. It is expected that due to climate change there will be more intense floods during the coming decades. Therefore, it is important to improve the current understanding about the recharge that may occur during such extreme events. We perform simple first-order analytical estimates of focused recharge during flood events and use them to calculate potential watershed-scale recharge. We demonstrate that rapid and significant recharge to groundwater during flooding events may occur, being the main recharge mechanisms in hydrological systems located in arid and semi-arid areas. Such potential may have great significance in those regions where groundwater is the main or sole water source. For example, we estimated that the recharge that may occur during a single flood event of a few days duration can be equivalent to more than 30 times the mean annual rainfall recorded in some arid regions. We also show that the time that infiltrated water requires to travel through the vadose zone to reach relatively deep water tables can be less than a few hours under reasonable assumptions.