Optimization of Dimension of Crescent Pond Structures in Micro Catchments (Case Study: Dry Farming Land of Estahban in Fars Province)

The crescent structure is one of the water harvesting systems that lacks precision in design, especially in the precision of intake volume of the crescent that may cause damage. The study area includes sloped lands in which figs are grown through dry farming by using the runoff that is collected by the crescent structure. The purpose of this study is to optimize the dimensions of crescent pond structures in Estahban of Fars province. Therefore, a maximum of 24-hour rainfall data for 20 years (1995-2014) from the Estahban station was used in this study. After analyzing the data in terms of accuracy and homogeneity, the time series data were fitted to different functions and after selecting the best distribution function with respect to residual sum of squares, the maximum 24hour rainfall on different return period was calculated. Then, the SCS method was used for calculating the runoff and based on of the 100 square meters area of each micro catchment, the volume of runoff was calculated. The results showed that the use of the log Pearson type ΙΙΙ distribution parameters is the best compared with other functions. By selecting a return period of 10 years as the basis for design and considering the different slopes, the volume of the crescent structure must have a capacity exceeding 2.33 cubic meters in order to increase the likelihood of success for the project.