فهرست مطالب eghbal ehsanzadeh

Intensity-duration-frequency rainfall curves are one of the hydrological tools for calculating hydraulic design of structures, watershed design, collection and disposal of surface water in cities. In this research, using the empirical formulas for the Ghareman (2004), Vaziri (1991) and Bell (1969), as well as Hyfran-plus hydrologic software, the rainfall intensity and intensity-duration-frequency curves was determined. At first, using rainfall intensities with time duration less than 180 minutes, a run test was performed in SPSS software and manually to ensure the homogeneity of the data. Then, different statistical distributions were fitted to the data to calculate rainfall intensity in different return periods. The chi square (K2) fitness tests was used to determine the optimal statistical distribution. The results showed that inverse gamma statistical distribution compared to other distributions had the highest accuracy in determining rainfall intensity. In the next stage, the intensity of rainfall during different return periods was calculated by empirical formulas using daily rainfall data and maximum daily precipitation. Comparison of the results of the empirical models and the hyfran plus software used in this study showed that the maximum difference of rainfall intensity in long duration is less than 1.6% and in short-term duration less than 20.2%. Also, the difference between predicted rainfall intensity in Vaziri (1991) and Bell (1969) empirical models is less than 19.8 percent.

Surface water collection networks are responsible for collecting, transporting and directing runoff to the nearest acceptable outlet. In this research, simulation and evaluation of Ilam City runoff system with the ASSA mathematical model developed by the Autodesk Inc. was carried out. In the present research, the entire study area, which includes in-city and outsides, was divided into 46 sub-basins. The physical properties of each sub-basin were determined using the ArcGIS software and field investigation. Within the Ilam City there are four main channels that lead the runoff of sub-basins out of the city. The runoff from sub-basins was calculated using three methods of rational, modified rational and SWMM. The results of the study showed that the collecting system only had a flood transfer ability during the two year return period and during the return periods greater than five years the major part of the main channels in the city were waterlogged and damaged.