Groundwater Evaporation and Recharge for a Floodplain in a Sub‐humid Monsoon Climate in Ethiopia

Abstract

AbstractGroundwater levels are declining at unsustainable levels in many areas of the world. To secure this resource for future generation, well‐documented groundwater level observations are needed to derive recharge rates and sustainable withdrawal amounts. Although groundwater is routinely monitored in most of the world, relatively little information is available in sub‐Saharan Africa including the Ethiopian highlands where groundwater irrigation could greatly increase food security. To obtain sustainable withdrawal rates for the wet Ethiopian highlands, we selected the Fogera plain in the Lake Tana basin with a sub‐humid climate. Weekly groundwater levels were measured in 32 abandoned shallow wells over a 2‐year period in 2014 and 2015. Our observations showed that in the 2 years, the groundwater level reached the surface during the rainy monsoon phase around first week of August. At the end of the dry monsoon phase in May, the average groundwater table was at 4 m depth. The amount of water removed by evaporation during the dry phase was 850 mm year−1. This is replenished through recharge during the wet phase. Rain in excess of the recharge and evaporation is stored on the surface or converted to overland flow. The groundwater flowed slowly towards the lake, but water passing the lakeshore was not a significant term in the water balance of the plain. Irrigation from groundwater seems to be sustainable especially when rivers flood periodically. Copyright © 2016 John Wiley & Sons, Ltd.