Morphometric Analysis To Identify Erosion Prone Areas On The Upper Blue Nile Using GIS (Case Study Of Didessa And Jema Sub-Basin, Ethiopia)

Abstract

Basin morphometric analysis is a means of mathematically quantifying different aspects of a drainage basin. In this thesis, morphometric analysis of Didessa and Jema sub basin was done to assess the hydrological characteristics and soil erosion potentials based on the morphological characteristics. The study was carried out using DEM data (30 m by 30m) in GIS environment. The extracted drainage network for both sub basins has 5th order according to Strahler’s stream orders. The basic parameter (stream order, stream number, stream length, basin area, basin perimeter and basin length) from GIS software were used for analysis of Linear, areal and relief aspect of Morphometric parameter. The linear parameter (bifurcation ratio, drainage density, stream frequency and drainage texture ratio) and relief aspect parameter (basin relief, relief ratio and ruggedness number) have direct correlation with soil erosion. But the areal parameter (form factor, circularity ratio, elongation ratio and constant channel maintenance) have inverse relationship with soil erosion. The Average of all these parameter for each sub watersheds was calculated to determine the final priority classes and categorized as high ( 2.55), medium (2.55 to 3.55) and low ( 3.55). Moreover the final priority Map also indicates that; high priority classes of Jema sub watersheds covers larger area of about 7292.57km2 (49.45% ) for both J-3 and J-1, whereas 5099.43km2 (29.85%) of D-6 from Didessa sub watersheds were vulnerable to soil erosion. This indicates that comparatively; Jema watersheds were more vulnerable to soil erosion than that of Didessa watersheds where phase wise implementation of soil and water conservation measure has to be taken 1st. The Sub-Watershed (J-2 & J-5 from Jema and D-3 & D-4 from Didessa) 2nd priority were needed for reclamation and conservation process. The sub watershed (J-4 from Jema and D-1, D-2 and D-5 from Didessa) have a low risk of land degradation hence it should be given lowest priority in sub-basin conservation practices.