Modeling the spatio-temporal flow dynamics of groundwater-surface water interactions of the Lake Tana Basin, Upper Blue Nile, Ethiopia

Tibebe B Tigabu,Nicola Fohrer,Paul D Wagner,Georg Hörmann

doi:10.2166/nh.2020.046

Abstract

AbstractThe Ethiopian government has selected Lake Tana basin as a development corridor due to its water resources potential. However, combined use of groundwater (GW) and surface water (SW) is still inadequate due to knowledge gaps about the flow dynamics of GW and SW. Mostly, there is no information about groundwater use. Therefore, this study aims to investigate the dynamics of GW-SW interactions on a spatio-temporal basis in three of the main catchments (Gilgelabay, Gumara and Ribb) that drain into Lake Tana. To this end, the SWAT-MODFLOW model, which is an integration of SWAT (Soil and Water assessment Tool) and MODFLOW, is used. The results reveal strong hydraulic connection between the GW and SW in all the three catchments. In the Gilgelabay catchment, the flow from the aquifer to the river reaches dominates (annual discharge from the aquifer varies from 170 to 525,000 m3/day), whereas in Gumara (annual exchange rate between −6,530 and 1,710 m3/day) and Ribb (annual exchange rate between −8,020 and 1,453 m3/day) the main flow from the river reaches to the aquifer system. The flow pattern differs in the three catchments due to variations of the aquifer parameters and morphological heterogeneity. Overall, this study improves our understanding of GW-SW flow dynamics and provides insights for future research works and sustainable water management in the Nile region.

Highlights

Water availability and water quality are major challenges of the 21st century due to a growing water demand
Results from this study indicated that SWAT-MODFLOW can simulate the surface and subsurface hydrologic processes in the study areas and can provide insights into GW-surface water (SW) interactions
The capability of the model to produce reliable results was reflected by the good match of the simulated and observed streamflow data as well as by the comparison between observed hydraulic head values measured at water wells during the course of drilling and mean simulated hydraulic head values

Summary

Introduction

Water availability and water quality are major challenges of the 21st century due to a growing water demand. The challenge is twofold for developing countries like Ethiopia because of a limitation in technology and financial resources to invest in water resources development. Groundwater is the only reliable water supply option for most rural areas in Africa to meet the dispersed demand (Hiscock ). Extraction of water from the aquifer system is rarely regulated, resulting in over-pumping of the groundwater. The complete drying-up of Haramaya Lake in Eastern Ethiopia since 2005 is one example of the consequences of decreasing groundwater levels due to over-pumping for agriculture and household use (Abebe et al ). A comprehensive understanding of catchment hydrology is essential for sustainable water management in catchments with a strong groundwater (GW) and surface water (SW) interaction (Bailey et al ; Dowlatabadi & Zomorodian ; Guevara Ochoa et al )

Objectives

Methods

Results

Conclusion