Event-based runoff and sediment yield dynamics and controls in the
sub-humid headwaters of the Blue Nile, Ethiopia
Abstract
Land degradation due to soil erosion presents a challenge for
sustainable development. We investigated the impact of land use type and
land management practices on runoff and sediment yield dynamics in the
northwestern highlands of Ethiopia. The study area included 14
zero-order catchments with a surface area ranging from 324 m2 to 1715
m2. V-notch weirs produced from plastic jars were introduced as
measuring alternatives that met local constraints. Runoff depth at the
weir was registered at 5-min intervals during two rainy seasons in 2018
and 2019. Rainfall was measured using tipping-bucket rain gauges. Runoff
samples were collected in 1-L bottles and suspended sediment
concentration (SSC) was determined. The mean event runoff coefficient
ranged from 3% for forests to 56% for badlands. Similarly, the mean
annual sediment yield (SY) was lowest for forests (0.8 Mg ha-1 yr-1) and
highest for badlands (43.4 Mg ha-1 yr-1), with significant differences
among land use types (14.8 Mg ha-1 yr-1 in cropland, 5.7 Mg ha-1 yr-1 in
grazing land, and 2.9 Mg ha-1 yr-1 in plantations). Soil organic matter
(SOM) reduced runoff and SY, necessitating the consideration of
agronomic and land management practices that enhance SOM. Annual SY
decreased exponentially with the rock fragment cover (RFC). In fields
where RFC was less than 20%, collecting rock fragments for installing
stone bunds resulted in a net increase in SY. Rehabilitating badlands
and enhancing SOM content in croplands can substantially reduce
catchment SY and, hence considerably contribute to the sustainability of
this type of environment.