Estimation of the Curve Number and Runoff Height Using Arc GIS Software with the Arc CN-Runoff Tool (Case study: Nazluchai Basin of Urmia)

Estimating the runoff height potential is important for managing and predicting the flooding of an area. In this regard, the US Soil Conservation Agency (SCS) has provided a method that is very suitable for areas lacking hydrological data. Conventional runoff measurement methods are very costly, time consuming and difficult. The purpose of this study was to calculate the flooding potential and draw a map of the Nazlouchai Watershed curve number by the SCS method. Land use map of the area was compared with the index table and integrated with the soil hydrologic group data, and the runoff curve number, an important factor in the SCS method, was obtained. In the next step, the average rainfall curve number, and runoff height were calculated, and the results were zoned according to the curve number and runoff height maps. Using the Geographic Information System, the average weight of the area curve number was estimated as 96.77. Results showed that the highest amount of runoff curve number under the average humidity conditions in the study area was 100, and the lowest value was 56.00. The high mean value of the area curve number indicates the low permeability of the area, which indicates the strong likelihood of flood occurrence.