On-site financial costs of soil erosion by runoff from the Mizewa catchment of the Blue Nile basin

This study was conducted in Mizewa watershed which is located in Blue Nile Basin (BNB) to estimate on-site financial cost of erosion in terms of yield reduction taking maize as representative crop. For this purpose, discharge measurement and runoff sampling was made during the rainy season of 2011 at the outlet of three sub watersheds within Mizewa catchment; lower Mizewa (MZ0), Upper Mizewa (MZ1) and Gindenewur (GN0). The samples were filtered to separate the sediment which was subsampled for determination of suspended sediment concentration (SSC), sediment fixed NO3 -, NH4 + and available phosphorous (P) contents. The filtered water was used to assess dissolved nitrate and dissolved phosphate. The on-site financial cost of erosion was estimated based on productivity change approach (PCA) focusing on available NP losses. The result revealed that the SSC and its NP content varied in space and time, in which higher and lower SSC occurred towards the beginning and end of the rainy season, respectively. The mean seasonal discharge was found to be 2.12±0.75, 1.49±0.52 and 0.57±0.20 m3/ sec at MZ0, MZ1 and GN0 stations in that order while the corresponding sediment concentration was 510±370 mg/l, 230±190 mg/l and 370±220 mg/l. This led to the total suspended sediment loss (SSL) of 4 ton/ha/year, 2 ton/ha/year and 3 ton/ha/year from the respective subwatersheds. The on-site financial cost due to N and P lost associated with SSL was estimated to be USD 200/ha, USD 186/ha and USD 227/ha from MZ0, MZ1 and GN0 watersheds, respectively. The study revealed that the economic impacts of soil erosion which is variable based on the characteristics of land resources and management practices are immense and deserve due attention. The result may help in sensitizing both farmers and decision-makers about the risk of soil erosion and in targeting management practices to overcome the challenges

Impact of water harvesting ponds on household incomes and rural livelihoods in Minjar Shenkora district of Ethiopia

This paper presents the findings of the socio-economic impact of household-level water harvesting technology. Before water harvesting was introduced, onions were not grown in the area due to lack of seedlings. Thus onion seedlings were grown on 100 m2 plots using water from the ponds in the dry season, then sold or planted under rainfed conditions during the rainy season. The results obtained show that the average net income from onion seedlings was 155 USper 100 m 2 plot, while those from bulb onions grown rainfed in the field was 1848 US per ha, making the contribution to farmer incomes by onions alone about 2003 US$ per year which is higher than from rainfed teff and wheat combined

Scenario-based decision support for an integrated management of water resources

© 2017 International Association for Hydro-Environment Engineering and Research. In this study, analyses of future scenarios of water demand and supply as well as an assessment of trade-offs for water allocation across the different water use sectors in the upper Blue Nile basin are made. Different periods of regulation of Lake Tana (Ethiopia) and subsequent impacts on the lake level hydrological regime are investigated. A decision support system is developed and available water supply for normal- and low-flow hydrological conditions are determined based on recorded flow data and a simple rainfall-runoff model. Different scenarios have been triggered and simulations are conducted to understand the implications of planned water resource developments in the area. We found that the annual inflows to Lake Tana under an average hydrological condition are about 5.7 × 109 m3 and are estimated to reduce by about 27% when all planned water resources development projects are implemented in the catchment. These projects aim at the generation of 460 MW hydroelectric power and about a billion m3 per annum supply of water to the large-scale irrigation schemes. During low-flow conditions, supply will run short of demands and the lake water level can drop by 0.3 m from the natural outlet level (1785 m a.s.l). Lake water levels and long-term lake level fluctuations have been affected significantly due to regulation with subsequent impacts on the lake ecology. An upstream–downstream cooperation, transparency and participation in the decision making and establishment of an adequate data acquisition system are critically important elements in the management of water resources in the basin.status: publishe