Recharge–Discharge Relations of Groundwater in Volcanic Terrain of Semi-Humid Tropical Highlands of Ethiopia: The Case of Infranz Springs, in the Upper Blue Nile

Fenta Nigate,Kristine Walraevens,Alemu Yenehun,Ashebir Sewale Belay,Marc Van Camp

doi:10.3390/w12030853

Abstract

The major springs in the Infranz catchment are a significant source of water for Bahir Dar City and nearby villages, while sustaining the Infranz River and the downstream wetlands. The aim of the research was to understand the hydrogeological conditions of these high-discharge springs and the recharge–discharge relations in the Infranz catchment. The Infranz catchment is covered by highly pervious and young quaternary volcanic rocks, consisting of blocky, fractured, and strongly vesicular scoriaceous basalt. At the surface, these rocks crop out as lineaments forming ridges, delimiting closed depressions in which water accumulates during the rainy season without causing surface runoff. Geology and geomorphology thus combine to produce very favorable conditions for groundwater recharge. Three groundwater recharge methods were applied to estimate groundwater recharge and the results were compared. Groundwater recharge was calculated to be 30% to 51% of rainfall. Rapid replenishment raises the groundwater level during the rainfall period, followed by a rapid decline during the dry season. Shallow local flow paths discharge at seasonal springs and streams, while more regional and deeper flow systems downstream sustain the high-discharge springs and perennial Infranz River. The uptake of 75% of spring water for the water supply of Bahir Dar City, local extraction for domestic and small-scale irrigation use from springs, rivers and hand-dug wells, encroaching farming, and overgrazing are exacerbating wetland degradation.

Highlights

Groundwater is the major source of fresh water across the globe where human and ecological communities depend on it [1]
The high values ranging from 33% to 51% we found in this study are due to the specific geological conditions of the Infranz catchment, with the highly vesicular and fractured scoriaceous young Quaternary basalts, and the typical geomorphology with the closed depressions surrounded by the low basalt ridges
Local shallow flow systems discharge into seasonal springs and stream, while a regional flow system sustains the high-discharge springs and downstream perennial Infranz River

Summary

Introduction

Groundwater is the major source of fresh water across the globe where human and ecological communities depend on it [1]. Sometimes groundwater can become critical to survival when surface water resources run dry during a severe drought. The dynamics, mainly recharge–discharge conditions of groundwater, are essential for the sustainable use of groundwater which affects groundwater-dependent streams, wetlands, and ecosystems [2]. The recharge–discharge mechanism of groundwater highly differs from place to place and depends on different variables. Groundwater occurrence and dynamics in Ethiopia, in the Tana basin, are complex, which is attributed to the wide heterogeneity of geological, geomorphological, topographical, and hydro-climatic conditions [2,3]. Understanding the controls of the recharge–discharge mechanism of groundwater for a given area is essential for the sustainable use of this precious resource

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Conclusion