Effects of check dams on runoff characteristics along gully reaches, the case of Northern Ethiopia

Abstract

In the Highlands of Northern Ethiopia soil and water conservation (SWC) practices, including construction of check dams in gullies, have been widely implemented for the last three decades. Despite this extensive installation of check dams, their effects on runoff response are not well understood as compared to those of other SWC practices. Hence, this study examines the effects of check dams on runoff response in gully channels. 90 degree V-notch weirs were installed to measure a wide range of runoff discharges at the upper and lower sections of five gully reaches: two channel cut in sandstone (a gully with check dams and vegetation (SCV) and an untreated gully (S)) and three cut in limestone (an untreated gully (L), a gully with check dams but no vegetation (LC) and a gully with check dams and vegetation (LCV)). Automatic sensors were installed to monitor runoff depth during two rainy seasons (29/08/14 -17/09/14 and 24/7/15 -14/09/15). All runoff characteristics at the lower section of each gully reaches were calculated for a gully reaches length of 50 m. In the sandstone area, the results show longer lag times of runoff to reach the lower section of the channel reach in the treated gully (SCV) compared to the untreated gully: difference in time lag equal lag to production of runoff equals 51% for runoff initiation, 61% for peak runoff and 44% for runoff end. An increase of hydraulic roughness by check dams and water transmission losses in deposited sediments are responsible for the delay of runoff to reach the lower part of the gully channels. In the limestone area, different time lags were recorded in different gully reaches regardless of the treatment effects (lag to runoff initiation, lag to peak flow and lag to runoff end were larger at LC, L and LCV, respectively). The reduction of peak runoff discharge between the upper and lower gully sections was larger in the gullies with check dam and vegetation (8% -17%) than in gullies without treatment (5% -6%). Reduction of runoff volume between these 2 gully sections was also larger in treated gullies than in untreated gullies: i.e. 18%, 9% and 8% in SCV, LCV and LC, respectively while it was only 4% in S and 6% in L. This study shows that the implementation of check dams combined with vegetation reduced peak flow discharge and runoff volume as large sections of runoff infiltrated in the sediments deposited behind the check dams. As gully check dams are implemented in a large areas of the North Ethiopia Highlands, this contributes to groundwater recharge and increased river baseflows.

Change in low flows due to catchment management dynamics—Application of a comparative modelling approach

“…The different types of terraces and deep trenches constructed across the slopes that follow the contour of the field enhanced soil infiltration capacity of the catchments. Most of the terraces in the catchment constructed in hillslopes and plateau have significantly reduced overland flow and increased the soil moisture (Haregeweyn et al, ; Gebremeskel et al, ; Guyassa et al, ). These structures are the main explanatory candidate for the increased low flow proportion during the dry seasons.…”

“…A number of local studies (e.g. Alemayehu et al, ; Haregeweyn et al, ; Gebremeskel et al, ; Guyassa et al, ; Nyssen et al, ) has also shown that implementation of SWC structures in watersheds resulted in a decrease of surface runoff volume and enhanced availability of water during the dry months. Similarly, some studies (Gebreyohannes et al, , ; Taye et al, ) support the finding of this study that groundwater has significantly increased in the previously degraded lands of the region.…”

The Changing Relationship Between Rainfall and Surface Runoff on the Loess Plateau, China

“…These changes enhance the ability of the soil to resist rainstorm erosion, and instantaneous infiltration intensity increases (because increased roughness allows more time to infiltrate); therefore, infiltration‐excess runoff became a little more difficult to generate in the P2 period. In addition, leaf litter and check dams further promote water infiltration (Guyassa et al, 2017). In other words, more monthly rainfall is needed to keep monthly rainfall and monthly infiltration changing synchronously.…”

“…As is illustrated by Remaître et al (2008), maximum flow height and maximum velocity of debris‐flow events decreased by 63% and 66%, respectively, comparing a scenario with no check dams with a scenario involving 75 check dams. In addition, infiltration around rivers with check dams tends to increase because check dams allow more time for surface runoff (Guyassa et al, 2017). Moreover, they can change channel slopes by intercepting sediment load from upstream, leading some channel lands to develop into a relatively flat landscape.…”

Dynamics of ephemeral streams at the foot of degraded catchments in northern Ethiopia

“…Correlation between maximum 1 hr rain intensity per event and daily rainfall, for two stations in the central and northern Ethiopian highlands: Doketu near Holeta in central Ethiopia (9.246158°N, 38.372717°E) and Adi Kalkwal near Hagere Selam in northern Ethiopia 13.657005°N, 39.210149°E (Guyassa, Frankl, Zenebe, Poesen, & Nyssen, ) [Colour figure can be viewed at wileyonlinelibrary.com]…”