Development of Intensity-duration- Frequency Curves “idf” for Dohuk City in Kurdistan Region of Iraq

Abstract

Dohuk city is hydrologically located in a relatively narrow watershed bounded by mountain ridges with heavy rainfall seasons. Due to its topographical characteristics and rapid urban development, the city is prone to floods during intense rainfall events or storms and in need of a proper storm water drainage system and flood control hydraulic structures for managing intense storm rainfalls, avoiding urban flooding, property loss, and most importantly human casualties. Nevertheless, the local civil engineers are in need of having up-to-date hydrological formulas, relationships, and information in order to be able to adequately design the flood control hydraulic structures. One of these important relationships is IDF curves which correlates the Intensity, Duration, and Frequency of an observed rainfall event. The authors have been able to develop updated IDF curves and empirical intensity formulas for Dohuk city by converting maximum annual rainfall readings for 21 consecutive years (2000-2020) into sub-daily rainfall records for durations of 10, 20, 30, 60, 120, 180, 360, 720, 1440 minutes with recurrence intervals of 2, 5, 10, 25, 50, 100 years using Gumbel and Log Pearson distribution (LPT III). The accuracy and reliability of the results were statistically confirmed through applying coefficient of determination with the value of (R2=1) and Goodness of fit test (Chi-square) with the confidence degree of (95%)