Impact Of Land Use Land Cover Change On Surface Runoff: The Case Of Ambo Town, Ethiopia

Abstract

The Impact of Land use Land cover change over the world currently develops direct and indirect impacts on surface runoff. Expansion of Ambo town urban areas causes the reduction of Huluka river watershed potential which is the main source of water supply and other miscellaneous use for the residents of Ambo town. Because of increasing of urbanization, floods are the main causes to affect the property, buildings, and infrastructures in case of Ethiopia. The main objective of this study was Impact of Land use Land cover change on surface runoff in the case of Ambo town on Huluka river watershed. Satellite image downloaded for 1997, 2005 and 2011 of the watershed area was taken based on the quality of data and the available resolution. Excel statistical software was used for filling missing value of precipitation data and data consistency was checked up using double mass curve. The surface runoff generated from the watershed was estimated based on the rainfall intensity and major characteristics of the watershed area which are the major factors for designing urban storm water drainage facilities and structures. Arc Geographical Information System and Geographical Information System extension tools were used to extract hydrological characteristics of the watershed; Hydrologic Engineering Center Hydrologic Modeling System to simulate rainfall - runoff process and Hydrologic Engineering Center River Analysis System for flood inundation assessement. The daily rainfall and stream flow data was used for Hydrologic Engineering Center Hydrologic Modeling System calibration and validation. To evaluate the accuracy of the model, calibration and validation was conducted. Nash Sutcliff efficiency during calibration and validation was 0.744 and 0.72 respectively where as coefficient of determination during these two processes was 0.8556 and 0.8122 respectively. The hydrological and hydraulic modeling are accomplished by dividing the watershed in to different sub-basin. Hydrological modeling depending on land use/land cover of the peak discharge was generated 1997, 2005 and 2011 at the outlet was 36.5, 47.56 and 61.04 m3/s respectively. The peak discharge simulated by frequency storm method for 10, 25, 50 and 100 return periods was 38.2, 47.2, 54.2 and 61.4m3/s. The result found from Hydrologic Engineering Center Hydrologic Modeling System frequency storm method used for flood inundation map generation. Flood inundation maps produced using Arc Geographical Information System to visualize flood depth and extent for each return period. Accordingly, maximum flood depth of 17.7632, 17.8779, 17.9548 and 18.0347m for 10, 25,50, and 100 year return periods respectively was found with flood extent of 97.58, 100.56, 103.34 and 105.54 ha for 10, 25, 50 and 100 year return periods at the middle of the final reach of the study area.