MORPHOMETRIC ANALYSIS OF THE SOUTHERN AL JABAL AL AKHDAR CATCHMENT

Abstract

The study aimed to quantify the morphometric characteristics of 11 watersheds in south Al Jabal Al Akhdar area (Green Mountain)  located on northeast Libya. Where Digital Elevation Model (DEM) data of 1 arcsec resolution for the study area downloaded from USGS Earth Explorer and processed to extract the watershed attributes using ArcGIS software. In addition, the linear, areal, and relief aspects parameters and indices were computed. The stream number for the watersheds varies from first orders to seventh orders, where a large number of streams was found in the first, second, and third orders. Drainage networks of the watersheds are a dendritic pattern reflects the subsurface lithology. The total lengths of streams in the study area are 35757.8 km. Also, the correlation coefficients which calculated for the relationship between the stream number and the stream count and lengths showed strong inverse relation. Moreover, observed bifurcation ratio for the watersheds considered as low with exception of the seventh order in some watersheds, where the streams tend to be braided due to the stream runoff through the depositional zone that consisting of recent uncompacted fluvial deposits. Drainage densities in the study area are coarse which indicated the much susceptibility to flooding and soil erosion. Where the drainage texture in the study area mostly is very coarse with the exception of some watersheds those are considered as coarse texture. Stream frequencies show very low values. Furthermore, the length of overland flow classified as moderate. The results of relief aspects computation show variation among the watersheds from high to low values. For the ruggedness number values, all watersheds show sharp morphology. Finally, The morphometric characteristics of the watersheds show moderate geomorphologic characteristics, stability in tectonic geology, and homogenous lithology, also the watersheds have intermediate to low flooding susceptibility but in case of heavy rainstorms a very strong flash flood may occur, as the upper stream areas of the watersheds prevail high risk of soil erosion, therefore flood protection ,and  soil conservation measures are crucially demanded in the study area especially in the northern parts.