Fourth Edition
Programme
Young Researchers Overseas Day
15 December 2020
Young Researchers’ Overseas Day Royal Academy for Overseas Sciences Brussels, 15 December 2020
69
Runoff response to land management in small catchments near Lake Tana, Ethiopia Assaye Habtamu
1,2*, Nyssen Jan
1, Poesen Jean
3,4, Lemma Hanibal
5, Tsegaye Meshesha Derege
2,
Wassie Alemayehu
2, Adgo Enyew
2& Frankl Amaury
1Keywords. — Sub-catchment; Quick Flow; Stone Bunds; Curve Number; Lake Tana Basin.
Summary. — The highlands of Ethiopia are severely affected by soil erosion by water. Consequently land management practices such as stone bunds have been widely implemented in recent years. Here, we investi- gate the effect of stone bunds and vegetation on steep slopes on quick flow (direct flow due to rain storm) in six small catchments (20 – 80 ha), which are dominantly agriculture and have seasonal streams. Hydrological monitoring stations were installed at the outlet of each catchment, and discharge and rainfall were recorded every five minutes during the rainy seasons of 2018 and 2019. Event-based quick flows (Qd) were analyzed against rainfall (P) and catchment characteristics. Quick flow was also predicted with the Natural Resources Conservation Service “Curve Number” (NRCS-CN) method, which is an empirical model used to predict ru- noff based on hydrologic soil group, land use and antecedent moisture condition. Calibration of the NRCS-CN runoff model based on observed Qd and P resulted in an Summaryion coefficient (λ) (which is a ratio of the initial Summaryion to maximum potential retention) value of 0.014, much less than the commonly used 0.05.
CNs in July and August are higher than June and September due to high antecedent moisture condition and showed declining trend with increasing stone bund densities. In catchments with high density of stone bunds and vegetation on steep slopes the quick flow was reduced by 43 % compared to catchments without conserva- tion structures; implying that stone bunds and vegetation rehabilitation implemented so far have been effective in reducing quick flow and enhancing soil infiltration and ground water recharge. Based on our results, a value of λ = 0.01 is recommended for runoff prediction using the NRCS-CN method in the sub-humid Ethiopian highlands, rather than the commonly accepted 0.05. Besides, ongoing efforts of soil and water conservation in the highlands of Ethiopia should be promoted in catchments where quick flow is high due to land degradation.
1 Department of Geography, Ghent University, Ghent, Belgium.
2 Department of Natural Resource Management, Bahir Dar University, Bahir Dar, Ethiopia.
3 Department of Earth and Environmental Sciences, KU Leuven, Heverlee, Belgium.
4 Maria-Curie Sklodowska University, Faculty of Earth Sciences and Spatial Management, Krasnicka 2D, 20-718, Lublin, Poland.
5 School of Civil and Water Resources Engineering, Bahir Dar University, Bahir Dar, Ethiopia.
* Corresponding author. Email: [email protected]
