Investigation of Depth-Area-Duration Curves for Kurdistan Province

Determining Depth-Area-Duration (DAD) curves in drainage basins is one of the applied researches in hydrology. DAD curves exhibit the depth and the area covered by the rainfall with a particular duration. DAD analysis is widely used in characterization of precipitation extremes for specification of so-called design storms. In this study the DAD curves for the Kurdistan province were prepared and investigated. To obtain the rainfall rate for different parts of the region for time durations of 24, 48, 72 and 96 hours, the daily rainfall data from the stations of the Ministry of Energy were studied first and the rainfall data for durations of one to four days were extracted afterward. 19 storms were then selected for the four time durations according to the rule of extensive rainfalls. The rainfall data from the interior meteorology stations and from some of the stations of the neighborhood provinces at the same occurrence time of the last storms were extracted and recorded according to their termination time. In order to determine the average of maximum rainfall depths for different durations for each storm, calculations were performed using isohyetal maps which were prepared by ‘Moving Average’ method. The initial DAD curves were then prepared using those calculations. Since the maximum rainfall is needed, the initial DAD curves for each duration were combined to obtain a final DAD curve, which is basically the envelope depth-area curve for the corresponding duration. This procedure was performed for all four time durations and ultimately four final DAD curves, one per each time duration, were produced.