Environmental Implications of Soil Erosion and Sediment Yield in Lake Hawassa Watershed, South-central Ethiopia

Abstract

Background: Assessing soil erosion, sediment yield and sediment retention capacity of watersheds is one of the under researched areas in watersheds of developing countries like Lake Hawassa watershed. The study examined soil erosion, sediment yield and sediment retention and their environmental implications in Lake Hawassa watershed. The quantification and mapping was carried out using Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model. Data such as Land Use Land Cover (LULC), Digital Elevation Model (DEM), rainfall, soil, and management practice were used as input parameters.Results: The empirical analysis confirmed that the watershed has a total soil loss of about 5.27 Mt annually. The mean annual erosion rate from the watershed was estimated to be 37 t ha-1 yr-1. The estimated erosion rate was greater than the maximum tolerable erosion limit in Ethiopia (2-18 t ha-1 yr-1). The total amount of sediment which was exported to the nearby streams and lakes in the watershed was estimated to be 1.6 t ha-1 yr-1. The water bodies receive a total of 226,690.3 t of sediment annually. Although higher soil loss and sediment export per unit of area were estimated from the highest slope gradients, greater contributions to the total soil loss and sediment export were computed from slopes with 5-30% gradients. In terms of LULC, the highest contribution to the total soil loss was computed from cultivated land while the highest rate of soil loss per hectare was observed from bare land. Due to the existing vegetative cover, a total of 18.65 Mt (130.7 t ha-1 yr-1) of sediment was retained. Vegetation-covered LULCs such as forest, woodland, shrub land, and agroforestry revealed the highest sediment retention capacity. As a result of the increasing soil erosion and sediment yield in the watershed, a drying of a small lake and the rise in the water level of Lake Hawassa were identified. Conclusion: Most of the soil loss and sediment yield were contributed by small part of the watershed. Thus, the results underscore the urgent need for targeted soil and water conservation measures of various types to ensure sustainability of the watershed resources.

Land-use/land-cover changes and implications in Southern Ethiopia: evidence from remote sensing and informants

“…The magnitude of LULC change differs with the slope gradient and elevation range. The higher soil loss and sediment export were estimated from the highest slope gradients, from slopes with 5–30% gradients ( Degife et al., 2021 ). They reported the 1.6 ton per hectare per year of sediment exported to Hawassa watershed and water bodies.…”

“…In the basin, there is a high competition for irrigation water, decline of natural woodlands, overgrazing, and cultivation of steep slopes experiencing several featured practices. In the basin, the LULC change trends showed a decline in woodlands, soil erosion, crop yield reduction, sediment yield, drying of small lakes and raise in lake levels ( Garedew et al., 2009 ; Godebo et al., 2018 ; Elias et al., 2019 ; Degife et al., 2021 ). Accordingly, the Rift Valley Basin faced with intensive land cover changes in the current years.…”

Spatiotemporal dynamics of soil loss and sediment export in Upper Bilate River Catchment (UBRC), Central Rift Valley of Ethiopia

“…Generally, soil loss and sediment export negatively affect ecosystem services and functions ( Degife et al., 2021 ; Yohannes et al., 2021 ). It aggravates rocky desertification ( Guo et al., 2022 ).…”

“…Soil loss affects agricultural productivity ( Wolka et al., 2015 ). That affects the rural population's food and nutrition security ( Degife et al., 2021 ; Haregeweyn et al., 2017 ; Yigez et al., 2021 ). It also causes environmental and socio-economic problems due to sediment load in the downstream area.…”

Influência do padrão da paisagem na qualidade da água: contribuições para a conservação dos serviços ambientais hidrológicos

“…12 Para fins comparativos, estimativas para outros estudos com o InVEST SDR foram de 3,6% a 26% para subbacias na Etiópia (áreas de 48 km² a 192 km² e 1426 km²) (ANESEYEE et al, 2020;DEGIFE;WORKU;GIZAW, 2021), 7,7% para uma microbacia (75 km²) em São Pedro -SP (ROSÁRIO; GUIMARÃES; VIANI, 2019), e 6,1% até 10,5% utilizando diferentes parametrizações para a sub-bacia das Posses (12 km²) em Extrema -MG (SAAD et al, 2018).…”