Connecting hillslope and runoff generation processes in the Ethiopian highlands: the Ene-Chilala watershed

Authors: ADDISIE, MESERET - National Center For Agriculture And Forestry Technologies (CENTA); AYELE, GETANEH - Bahir Dar University; HAILU, NIGUS - Bahir Dar University; Langendoen, Eddy; TILAHUN, SEIFU - Bahir Dar University; SCHMITTER, PETRA - International Water Management Institute, East Africa And Nile Basin Office; PARLANGE, JEAN-YVES - Cornell University; STEENHUIS, TAMMO - Cornell University

Submitted to: Journal of Hydrology and Hydromechanics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2020
Publication Date: 10/19/2020
Citation: Addisie, M.B., Ayele, G.K., Hailu, N., Langendoen, E.J., Tilahun, S.A., Schmitter, P., Parlange, J., Steenhuis, T.S. 2020. Connecting hillslope and runoff generation processes in the Ethiopian highlands: the Ene-Chilala watershed. Journal of Hydrology and Hydromechanics. 68(4):313-327. https://doi.org/10.2478/johh-2020-0015.
DOI: https://doi.org/10.2478/johh-2020-0015

Interpretive Summary: The understanding of hydrology is incomplete in the humid tropical monsoon climate and volcanic region of Ethiopia. Scientists from the USDA, ARS, National Sedimentation Laboratory in collaboration with researchers from Cornell University, International Water Management Institute, and Bahir Dar University, Ethiopia, studied the interactions between precipitation, infiltration, and surface and subsurface runoff over a four-year long period in the Ene-Chilala watershed, Ethiopia. Flow from the hillslope was as interflow, and appeared as saturated-excess overland flow in the valley bottoms as the groundwater table was close to the surface during the rainy phase of the monsoon period. The outcome of this study is intended to aid planning of sustainable watershed interventions in the (sub) humid Ethiopian highlands by improved understanding of the surface and subsurface hydrology.

Technical Abstract: Effective watershed planning requires an understanding of the hydrology. In temperate climates, these processes are well understood. However, the humid tropical monsoon climates, the understanding of watershed processes is incomplete especially in volcanic regions. The Ethiopian highlands is one of those regions. The objective is to better understand the hydrology of the volcanic regions in the humid tropics by linking the hillslope processes with the discharge at the outlet. The Ene-Chilala watershed was selected. The infiltration rate, piezometric water levels and discharge from two nested watersheds and at the outlet were measured during a four-year period. Infiltration rates on the hillsides exceeded the rainfall intensities. The excess rain recharged a perched hillside aquifer. Water flowed in the perched aquifer as interflow, saturating the valley bottoms. Perched water tables heights were predicted by summing up the recharge over the travel time from the watershed divide. Travel times ranged from a few days for piezometers close to the boundary to 40 days near the outlet. River discharge was predicted by adding the interflow from the uplands and overland flow from the saturated valley bottom lands. The predicted and observed values was good after the start to the end of the rain phase.