Applying SWAT Model to Estimate the Annual Runoff of Wadi Al-Mohammadi Basin, Western Iraq

Abstract

In arid and semi-arid regions, with unexpected periods of floods or droughts as a result of extreme variability in rainfall rates, runoff occurs in separate periods after clear occasional rainstorms. People living in these areas are greatly affected by water shortages during droughts and often have unsafe livelihoods. Wadi Al-Mohammadi is one of the main valleys in the Western Desert flows into the Euphrates River. It is considered an important area, due to many characteristics, including its relatively large area, the amount of water drained through, and has significant storage of groundwater, which is used mainly in agriculture and watering livestock, in addition to industrial purposes such as the production of washed sand, gravel that scattered on both sides of the valley. The Soil and Water Assessment Tool (SWAT) model is proven to be effective as a working platform in the hydrological cycle and to clarify its components and factors affecting the hydrological situation in a region. By applying the SWAT model using the required data set (LULC, slope, and soil types), Wadi Al-Mohammadi is subdivided into 199 HRU (hydrologic response units). The annual average flow discharge was 0.138 m3/s with an average annual water volume about 4.366 Mm3, while the average annual water volume is calculated from runoff which was of about 4.651 Mm3. There is a difference in the average annual volume of water calculated from surface runoff and discharge, due to a little slope, and not all the surface runoff water reaches the mainstream, or it ends in secondary valleys or collecting in pits, and there for the discharge is less than the surface runoff. Peak runoff is observed in Wadi Al-Mohammadi basin mostly during the winter season, from November to March.