Detecting the short term impact of soil and water conservation practices using stage as a proxy for discharge—A case‐study from the Tana sub‐basin, Ethiopia

Abstract

Efforts to tackle land degradation worldwide have spurred the adoption of soil and water conservation (SWC) practices intended to reduce surface runoff and erosion. Despite their widespread implementation, missing or incomplete monitoring remains a pervasive problem preventing evaluation of how well SWC practices meet these aims. When using runoff and sediment loss as main parameters to evaluate SWC efficacy, the key metrics are the production of flow per unit rainfall (runoff ratio), and exported sediment (sediment concentration). We develop a method to assess changes in these metrics in the absence of a flow rating curve, using more complete and reliable measurements of stage (flow depth). We apply these methods to datasets with incomplete rating curve collected from five watersheds included in the Tana and Beles Integrated Water Resource Development Project (TBIWRDP) in the Abay (Blue Nile) basin, Ethiopia. Changes in runoff ratio and sediment concentration relative to the first year of treatment varied by season. In the long wet season (Kiremt) that generates most runoff and erosion, reductions in runoff ratio and in sediment concentration occurred in four watersheds. Reductions in the runoff ratio were directly proportional to the areal density of SWC treatments in the watersheds, suggesting that SWC treatments were effective in controlling runoff and erosion.We suggest that stage and sediment concentration information can be used to assess watershed responses to SWC treatments. Focusing on these measurements, may facilitate the design of reliable and affordable monitoring programs, and ultimately facilitate improved financing approaches based on reasonable estimates of likely SWC practice performance.

The impact of stress factors on riparian and drawdown zones degradation around dams and reservoirs

“…However, these buffer zones are also among the most sensitive and often non‐recoverable natural ecosystems. Despite the increasing positive global effect of reservoirs, their riparian zones are changing and deteriorating owing to variations in land‐use patterns (Dempsey et al, 2017; Weldegebriel et al, 2021). The impacts of land‐use patterns on riparian health are complex (Castillo et al, 2012), and there is an urgent need to understand the relationship between land‐use variation and the condition of riparian zones in reservoirs (Mello et al, 2018; Yu et al, 2016).…”

To What Extent Is Hydrologic Connectivity Taken into Account in Catchment Studies in the Lake Tana Basin, Ethiopia? A Review

“…Furthermore, Akale, et al [80] noticed that conservation practices increased baseflow by 45% in Guale and 81% in Tikur-Wuha. Weldegebriel, et al [35] also looked at the fact that watersheds with more SWC treatments had less storm runoff.…”

“…Moreover, land use and land cover change modify the hydrological regime of the catchment [34]. Soil and water conservation treatments in the catchment can change the runoff ratio [35]. The numerous environmental problems in the Lake Tana basin have attracted many studies.…”

Assessment of Transverse Runoff in the Terraced Area for Adaptation and Mitigation of Climate Change

“…On the other hand, the soil erosion was severe when the field was not terraced and planted with pineapple across the contour line. As recommended [11][12] [13], reducing the hillslope gradient and length of the terrace and increasing the width of the terraced bench are beneficial to an increase in infiltration rates, reduction of runoff production, and surface flow velocity at the local scale.…”