Abstract
AbstractUnderstanding the natural low flow of a catchment is critical for effective water management policy in semi‐arid and arid lands. The Geba catchment in Ethiopia, forming the headwaters of Tekeze‐Atbara basin was known for its severe land degradation before the recent large scale Soil and Water conservation (SWC) programs. Such interventions can modify the hydrological processes by changing the partitioning of the incoming rainfall on the land surface. However, the literature lacks studies to quantify the hydrological impacts of these interventions in the semi‐arid catchments of the Nile basin. Statistical test and Indicators of Hydrological Alteration (IHA) were used to identify the trends of streamflow in two comparatives adjacent (one treated with intensive SWC intervention and control with fewer interventions) catchments. A distributed hydrological model was developed to understand the differences in hydrological processes of the two catchments. The statistical and IHA tools showed that the low flow in the treated catchment has significantly increased while considerably decreased in the control catchment. Comparative analysis confirmed that the low flow in the catchment with intensive SWC works was greater than that of the control by >30% while the direct runoff was lower by >120%. This implies a large proportion of the rainfall in the treated catchment is infiltrated and recharge aquifers which subsequently contribute to streamflow during the dry season. The proportion of soil storage was more than double compared to the control catchment. Moreover, hydrological response comparison from pre‐ and post‐intervention showed that a drastic reduction in direct runoff (>84%) has improved the low flow by >55%. This strongly suggests that the ongoing intensive SWC works have significantly improved the low flows while it contributed to the reduction of total streamflow in the catchment.
Highlights
Low flows are the dry season flow in a river where groundwater is the primary source (Bradford & Heinonen, 2008; Wittenberg, 2003)
Integrated catchment management interventions have been intensively implemented in the Agula and Genfel catchments since the mid-2000s but in different degrees
This study aimed at understanding the impact of these measures on the overall hydrological processes, the low flow modification in the catchments
Summary
Low flows are the dry season flow in a river where groundwater is the primary source (Bradford & Heinonen, 2008; Wittenberg, 2003). Accurate estimates of low flow characteristics in a catchment are fundamental for water resources development and management (Castiglioni et al, 2011; Laaha & Blöschl, 2006). To this effect, much of the focus on water management in arid and semi-arid regions has been on finding the balance between the incoming and outgoing water from rivers during the low flow periods (Giuntoli et al, 2013). SWC activities can cause visible changes in the dry season flow regimes (Gebremicael, 2019; Mu et al, 2007; Wang et al, 2013). Various studies (e.g. Schmidt & Zemadim, 2013; Abouabdillah et al, 2014) reported that the introduction of physical SWC structures can increase the base flow by >50%
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