ESTIMATION OF STORMWATER RUNOFF GENERATED IN BASRAH PROVINCE ROADS FOR DIFFERENT RAINFALL RECURRENCE INTERVALS

The main objective of this research is to estimate the surface runoff which is generated by rainfall for a residential area in Basrah Province, south of Iraq for different recurrence intervals of rainfall. The depth of runoff is based on changing of rainfall intensity when it exceeding the rainfall intensity of 17 mm / hr (the approved value in the design of the stormwater network in the area under consideration). Two common probability techniques (Weibull and Gamma distribution) were used for developing the relationship between annual maximum rainfall intensity and recurrence intervals. Weibull and Gamma probability distribution passed the Chisquared test for degree of freedom equaled to three. EPA Storm Water Management Model (SWMM) is used for simulating a rainfall –runoff routing process. Modified Green-Ampt method is used to describe the infiltration of water into the soil. Kinematic wave routing is used for routing flows through drainage system. The recurrence intervals have been used for estimating of surface runoff are ranged from 5 to 50 years with increment is equaled to 5 years. The depth of runoff is ranged from 16.2 mm for recurrence interval (5 years) to 29.6 mm for recurrence interval (50 years); these values are related to storm with duration is equaled to one hour, while it is ranged from 49.5 mm to 101.6mm for storm duration of three hours.