Drainage network extraction and morphometric analysis using remote sensing and GIS mapping techniques (Lesser Zab River Basin, Iraq and Iran)

The Lesser Zab River, in the northeast of Iraq and northwest of Iran, is the largest tributary inside Iraq supplying water to the Tigris River. The majority of the basin lies inside Iraq. The important goals of this study are to estimate the erodibility and flash flood hazard of the Lesser Zab River Basin (LZRB). The present research highlights sub-basins that should be prioritized for conservation and flood risk schemes. The morphometric analysis reveals that the most important sub-basins are Sb1 and Sb2, in terms of water contribution to the main river. They are characterized by higher stream order, larger area, high elevation, low drainage density, low drainage texture, and low relative relief. Because of the relatively high relief in the upper part of the LZRB, the sub-basins are characterized by low drainage density, which indicates more surface runoff compared to the main basin in the lower part. The very fine drainage texture in the upper part of the LZRB reflects low infiltration and higher runoff relative to the lower part. The sub-basins in the upper part of the LZRB, which have a low bifurcation ratio, produce flood hydrographs with marked discharge peaks, while the subbasins in the lower part, which have high ratios, produce low peaks over a long time period. Various morphometric parameters have been used for each sub-basin to calculate compound parameters for the final ranking of the subbasins. Based on utilization of morphometric parameters for the erodibility hazard assessment, sub-basins were divided into seven prioritization classes: critical, very high to critical, high to very high, medium to high, low to medium, very low to low, and lowest. Furthermore, the resultant hazard map indicates that 18 sub-basins have moderate to low risk of flash flooding and 29 sub-basins have low possibility of flash flooding.