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Title: The effect of community based soil conservation works on runoff and sediment loss in the Ethiopian highlands: case of Birr Watershed

Author
item AYELE, GETANEH - Bahir Dar University
item GESSESS, AZALU - Bahir Dar University
item ADDISIE, MESERET - Bahir Dar University
item TILAHUN, SEIFU - Bahir Dar University
item MOGES, MAMARU - Bahir Dar University
item ENKU, TEMESGEN - Bahir Dar University
item TENESSA, DAREGOT - Bahir Dar University
item Langendoen, Eddy
item NICHOLSON, CHARLES - Pennsylvania State University
item STEENHUIS, TAMMO - Cornell University

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/25/2015
Publication Date: 9/25/2015
Citation: Ayele, G.K., Gessess, A.A., Addisie, M.B., Tilahun, S.A., Moges, M.A., Enku, T., Tenessa, D.B., Langendoen, E.J., Nicholson, C.F., Steenhuis, T.S. 2015. The effect of community based soil conservation works on runoff and sediment loss in the Ethiopian highlands: case of Birr Watershed. In: Proc. 3rd International Conference on the Advancement of Science and Technology (ICAST-2015), May 8-9, 2015, Bahir Dar, Ethiopia. 8 pp.

Interpretive Summary: Since deforestation in the 1970s in-stream sediment concentrations in the Ethiopian highlands have increased significantly because of severe soil and gully erosion. Past soil and water conservation practices have not been effective to prevent this erosion in the (sub)humid highlands as they did not appropriately account for local rainfall-runoff processes. During the 2013 and 2014 rainy seasons scientists at the USDA-ARS National Sedimentation Laboratory in collaboration with researchers at Bahir Dar University (Ethiopia), Cornell University and Penn State University have monitored runoff and sediment concentrations in three subwatersheds of the Birr River watershed located south of Lake Tana, Ethiopia. Saturation-excess was the dominant runoff producing mechanism. Early in the rainy season sediment concentrations were highest in the degraded upslope areas of the watershed indicating contributions of hillslope erosion, whereas the bottomlands produced most soil later into the rainy season indicating gully erosion. Gully rehabilitation in combination with conservation measures on the degraded hillslope reduced sediment loads by 33% at the watershed outlet in 2014. Results of this study can be used by the Ethiopian government and foreign NGOs active in Ethiopia to develop more effective soil conservation measures.

Technical Abstract: Soil erosion is a serious problem in the Ethiopian highlands. Conventional erosion control approaches have generally been ineffective in halting this problem. The presented study measured precipitation, sediment yield and stream flow in 2013 and 2014 in the Ene-Chilala subwatershed of the Birr River watershed to quantify the watershed scale sediment loss before and after community participatory soil conservation practices installed on six gullies. Beginning in 2013 six gullies were rehabilitated by the community and researchers using biological and physical conservation practices such as: check dams constructed from gabions, wood and stones to reduce stream flow power; and upland soil conservation measures as part of the large scale soil and water conservation national program financed by the Amhara regional Bureau of Agriculture. In-stream monitoring was conducted at the watershed outlet (Weir-3) and two nested sub watersheds (Weir-1 and Weir-2). The amount of precipitation was recorded by automatic and manual rain gauges. The total precipitation was 1313 mm and 909 mm in 2013 and 2014, respectively. The infiltration capacity of the soil was measured at 18 locations for different slopes and land uses using single ring infiltrometer. The median infiltration capacity for upland and bottom land were 162 and 8 mm/h, respectively. The upland median infilitration was not exceeded at any time by rainfall intensities but the bottomland median infilitration was exceeded by rainfall intensity 34% of the time. The annual runoff at the watershed outlet was 781 mm and 392 mm in 2013 and 2014, respectively. Both upland and gully erosion were main sources of sediments in the rivers. The measured in-stream sediment concentration indicated high sediment concentration in the nested, hilly subcatchments at the beginning of the rainy season. Subsequently, active gullies on downslope saturated areas were dominant sources of sediment, which caused sediment concentration and sediment load at the watershed outlet (Weir-3) to exceed those at the upslope catchment outlets (Weir-1 and Weir-2). The annual mean sediment concentration was 24 g/l and 15 g/l in 2013 and 2014, respectively. The sediment concentration declined by 33% in 2014. The likely reasons were the community participatory rehabilitation of gullies in 2014 in addition to the upland soil and water conservation works through government mobilization and the low precipitation in 2014.