Hydrological Estimation for the Runoff of Qalachwalan Basin Using Hydrological Estimation for the Runoff of Qalachwalan Basin Using (SCS – CN) Method (2000 – 2020)

The surface water is a reflection of the climatic and topographical conditions of the basin in the study area, and affects the estimation of the amount of runoff water on the surface inside the basin. It is also possible to measure the amount of running water in the basin and know the periods of increase, and water scarcity in this quantity, on the other hand, take advantage from water for all fields and uses. Qalachwalan basin is one of the water basins located at north of the city of Sulaymaniyah with an area of (876.1) km2, and all of its water sources are within the borders of the Kurdistan Region of Iraq. Due to unsteady rain and heavy precipitation in the recent years, therefore, it was necessary to conduct some researches to know the size and amount of runoff, besides, to see if it is possible to benefit from it for the development and investment of the study areas. Accordingly, Soil Conservation Service- Curve Number (SCS – CN) Method has been used used to estimate the depth and amount of the annual runoff. From this study it became clear to us that the area has seven uses )Bodies of water, dense forests, agricultural lands, grasslands, residential lands, barren lands, paved roads. Besides, it appeared that the greatest amount of runoff, which lies in the grassland equals to (588523320) m3, and the smallest amount with (4442480) m3 lies in the forest area. So, we discover that the total amount of the basin water reached about (700141140) m3. Finally, our data are very vital for the local government and stakeholders in the future to how to deal with this water basin especially with unsteady precipitations.