Soil Erosion Modelling and Risk Assessment in Data Scarce Rift Valley Lake Regions, Ethiopia

Alemu Aga,Bayou Chane,Assefa Melesse

doi:10.3390/w10111684

Alemu Aga, Bayou Chane + Show 1 more

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https://doi.org/10.3390/w10111684

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Abstract

To prolong the useful life of lakes and reservoirs, prioritizing watersheds by severity and risk of soil erosion is an essential index to develop sound sediment management plans. This study aims to predict soil erosion risk and sediment yield using Soil and Water Assessment Tool (SWAT) model in Lake Ziway basin, Ethiopia, and the model result is validated with lake bathymetric changes. The SUFI-2 program was applied for a model calibration and the performance of the model was assessed. The catchment prioritization study indicated that some sub-basins having the same soil type and land use but a higher slope gives higher sediment yield. This confirms that, in the basin, the upland is the main source of sediment for the lake, hence the variation of sediment yield is more sensitive to terrain slope. Furthermore, the soil conservation scenarios demonstrated in SWAT that reduce the slope length of the watershed by 50% for a slope greater than 5% are decreasing the sediment yield of the basin by 55%. The bathymetric differencing of the lake indicates that the sediment was accumulating at a rate of 3.13 t/ha/year while a calibrated SWAT model resulted in 5.85 t/ha/year. The identified reasons for these variations are the existence of outlet for the lake, floodplain depositions and abstraction of sediment (sand mining) from the tributary rivers before flowing to the lake.

Highlights

Land degradation and soil erosion is a serious threat in agroecosystems and is one of the main global environmental crises [1]
H2 O/mm soil) (SOL_AWC.sol), surface runoff lag time (SURLAG.bsn), threshold depth of water in the shallow aquifer required for return flow to occur (GWQMN.gw), soil evaporation compensation factor (ESCO.hru), slope of water shed (HRU_SLP.hru), base flow alpha factor (ALPHA_BF.gw), groundwater delay (GW_DELAY.gw), and moist bulk density (SOL_BD.sol) with different sensitivity ranks
Curve number in a watershed is directly related to land use/cover and soil characteristics

Summary

Introduction

Land degradation and soil erosion is a serious threat in agroecosystems and is one of the main global environmental crises [1]. It has both onsite effects (loss of fertile topsoil) and offsite effects (sedimentation of lake and reservoirs). Loss of top fertile soil will reduce the productive capacity of the land and thereby create risk to global food security. The most significant and broadly impacting effects of sedimentation on lakes and reservoirs are changes in water balances, thereby reducing the live storage of the reservoir [2]. Reservoir storage is vitally important for agricultural irrigation, power generation, municipal water supply and other uses. To prolong the useful life of lakes and reservoirs, analyzing soil erosion risk is an important task to plan land use and soil conservation measures

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