Derivation of the Rainfall Intensity- Duration- Frequency Curve for Erbil city, Using SCS II Method

Abstract

Countries in the Middle East region are classified as arid and semi-arid regions in the world. Because of its geographical location, it is characterized by fluctuating rainfall, which is exposed to frequent floods and causes human and material losses, on the other hand there is a lack of short-duration interval rainfall data. Therefore, to achieve hydrological studies of floods and planning for flood mitigation structure, it is necessary to derive the Rainfall Intensity- Duration- Frequency (IDF) curve, as there is a traditional method for calculating IDF curves, which is based only on two statistical distributions and only one statistical test. In this research, Soil conservation service (SCS) Type II for 24-hour rainfall distribution suitable for the arid and semi-arid regions was adopted to derive the IDF curve for maximum daily rainfall data in Erbil city. The method used has few computational steps than the traditional methods, the number of parameters is less, the number of used statistical distributions is 6, and the number of statistical tests is 4, which increases reliability. The optimal distribution was chosen for Erbil city, and the IDF curves were derived. The maximum daily rainfall was used during a specified return period from 2 to 200 years. The results showed that the maximum difference between the IDF curves obtained from the SCS theory and the traditional method is about 11%. Also, empirical relationships for representation IDF Talbot, Bernard and Ishiguro were applied, and through the test, Bernard was found to be the best.

Keywords

• idf curve; max. daily rainfall; return period; scs; hyfran plus
• design rainfall storm.