Abstract. Soil erosion is one of the major factors affecting sustainability of agricultural production in Ethiopia. The objective of this paper is to estimate soil erosion using the universal soil loss equation (RUSLE) model and to evaluate soil conservation practices in a data-scarce watershed region. For this purpose, soil data, rainfall, erosion control practices, satellite images and topographic maps were collected to determine the RUSLE factors. In addition, measurements of randomly selected soil and water conservation structures were done at three sub-watersheds (Asanat, Debreyakob and Rim). This study was conducted in Koga watershed at upper part of the Blue Nile basin which is affected by high soil erosion rates. The area is characterized by undulating topography caused by intensive agricultural practices with poor soil conservation practices. The soil loss rates were determined and conservation strategies have been evaluated under different slope classes and land uses. The results showed that the watershed is affected by high soil erosion rates (on average 42 t ha −1 yr −1 ), greater than the maximum tolerable soil loss (18 t ha −1 yr −1 ). The highest soil loss (456 t ha −1 yr −1 ) estimated from the upper watershed occurred on cultivated lands of steep slopes. As a result, soil erosion is mainly aggravated by land-use conflicts and topographic factors and the rugged topographic land forms of the area. The study also demonstrated that the contribution of existing soil conservation structures to erosion control is very small due to incorrect design and poor management. About 35 % out of the existing structures can reduce soil loss significantly since they were constructed correctly. Most of the existing structures were demolished due to the sediment overload, vulnerability to livestock damage and intense rainfall. Therefore, appropriate and standardized soil and water conservation measures for different erosion-prone land uses and land forms need to be implemented in Koga watershed.

Dhaka, the capital of Bangladesh, is home to a population of 15 million people, whose water supply is 85% drawn from groundwater in aquifers that underlie the city. Values of Cl/Br >500 are common in groundwater beneath western Dhaka in areas <3 km from the river, and in rivers and sewers around and within the city. The study shows that groundwater beneath western Dhaka is strongly influenced by infiltration of effluent from leaking sewers and unsewered sanitation, and by river-bank infiltration from the TuragBuriganga river system which bounds the western limit of the city. River-bank infiltration from other rivers around Dhaka is minor. Values of Cl/Br and Cl concentrations reveal that 23 % of wells sampled in Dhaka are influenced by saline connate water in amounts up to 1%. This residual natural salinity compromises the use of electrical conductivity of groundwater as a method for defining pathways of recharge by contaminated surface waters. Concentrations of As, B, Ba, Cd, Cu, F, Ni, NO 3 , Pb, Sb, Se and U in groundwater samples are less than WHO health-based guideline values for drinking water.

Abstract. Soil erosion is one of the major factor affecting sustainability of agricultural production in Ethiopia. This research applied recently validated RUSLE soil erosion model based on 6 to 14 years data for the Ethiopian highlands to estimate soil erosion and to evaluate soil conservation strategies in the Koga watershed. In this study, the average annual soil loss rate determined is 30.2 t ha−1 yr−1. The lowest soil loss is estimated about 12.1 t ha−1 yr−1 around the outlet of the Koga river which is greater than the minimum tolerable soil loss (2 t ha−1 yr−1). The highest soil loss is estimated from the steep slopes of upper watershed which is 456.2 t ha−1 yr−1 by far higher than the maximum tolerable soil loss (18 t ha−1 yr−1). Using ordinary least square regression, existing land use aggravates soil erosion with 92 % overall coefficient of determination (R2). The topographic factor also influences soil loss with 89 % R2 value. Based on the evaluation of technical standards of soil conservation measures, 35.56 % of the existing soil conservation practices fit with the recommended national standard which has less contribution to tackle soil erosion. Therefore, to sustain agricultural practices, appropriate and standardized soil conservation structures on different erosion prone land uses and landforms should be implemented in Koga watershed.