Browsing by Author "Solomon, Berhane"

Now showing 1 - 1 of 1
  • No Thumbnail Available
    Item
    Understanding Runoff Generation Processes and Rainfall Runoff Modeling in Meja Watershed
    (Addis Ababa University, 2013-06) Solomon, Berhane; Birhanu, Zemadim (PhD); Dereje, Hailu (PhD); Assefa, Melesse (PhD)
    Understanding the basic relationships between rainfall, runoff, soil moisture and ground water level are vital for an effective and sustainable water resources planning and management activities. But so far there are no hydrological studies in Meja watershed that aims to understand the watershed characteristics and runoff generation processes. This study was conducted to understand runoff generation processes and model rainfall runoff relationship in Meja watershed having a drainage area of 96.6 km2.The watershed is one of the three research sites of International Water Management Institute (IWMI) developed in early 2010 in the upper Blue Nile Basin Ethiopia. In the study, primary data of soil moisture, shallow ground water level, rainfall and runoff were collected from the hydrological monitoring network in the watershed. Two nested sub- watersheds namely Galessa and Kolu were defined in the watershed for detail analysis of hydrologic variables. Galessa has drainage area of 1.6 km2 and Kolu has a drainage area of 2.5 km2. Hydrological models like HBV and RRL SMAR were configured to understand the relationship between rainfall and runoff in the watershed. Relationships between rainfall, soil moisture, shallow ground water level and runoff were developed to understand runoff generation processes in the watershed. Analysis of rainfall data indicated weak daily correlation (r2<0.35) of areal rainfall between Galessa, Serity and Kolu and similar annual total and average rainfall of the three sites of Meja watershed. However monthly correlation of areal rainfall between the three sites was better than daily correlation (r2>0.8). According to one year and three months data, there is no strong daily rainfall and runoff relationship (r2<0.5) in Meja and Kolu which is nested sub - watershed; this may be due to abstractions such as irrigation and human interventions in the watershed. Ground water level and runoff has strong relationship (r2>0.65) in monthly basis of Kolu nested sub watershed but there is moderate relationship of rainfall and ground water level. There is spatial variability of soil moisture content in Meja watershed, this variation occurs due to heterogeneity of the soil, which means the places are different in soil texture and also the variation is due to vegetation cover and change of slope. There is strong linear relationship of rainfall and monthly averaged volumetric soil moisture in most soil moisture layers of Meja and its nested sub-watersheds. The general relationship between runoff and monthly averaged soil moisture at different layers in Meja watershed and Kolu is strong. Analysis of rainfall runoff models indicated that relationships of rainfall with observed and simulated runoff was similar.HBV model performs better than RRL SMAR model in Meja and Kolu. RRL SMAR model couldn’t capture low flow in Meja and Kolu. This inaccurate result of SMAR model in Kolu sub-watershed may be due to inability of the model to simulate runoff in very small catchments like Kolu.