Experimental investigation of 3D flow over cluster microforms

Design storm estimating is one of the main step in designing and getting the size various structures and hydraulic installations. In some causes by which the capacity of system storage is considerable or returned period of design flood is long such as designing of the spillway of dams using of mathematical model for converting design storm to design flood is usual. In drawing pilgrim method a collection of registered severe rains at studied stations according to 8 base of time (1، 3، 6، 9، 12، 18، 24 and 36) is chosen. Then non-dimensioned cumulative chart is drawn on sheet and cumulative curve of average rain is exploited from each of mentioned continuations. In the Pilgrim method all rains of each continuation are considered and determined being meaningful or meaningless calculated patterns after determining of agreed tables and X2. In half method time distribution of rain is considered in the form of possibly distribution. In this method the shower of specified continuation depends on where the rainfall will be occurred in time-quarter are classified into groups. First shower quarter، second shower quarter، third shower quarter & forth shower quarter. Then the time-distributing of rain in each group is designed by two rainfall curves in from of cumulative rain and continuation of rain. It is represented in the form of 25% from the total time of rain. This methods are done in each of stations، and regional type patterns are gotten by using of all occurred rain. According to the obtained results of pointed possibly patterns، we can say that in the southern regions of province the most rainfalls are in the first quarter rain and in the south and eastern south are in the third quarter rains. The most observed rains in province are in first quarter and third quarter showers. According to the regional patterns، the rain of 1 and 3 hours are in the first quarter، the rain of 6 and 24 hours are in the third quarter and the rain of 9، 12 and 18 are in the forth quarter. The rain of 36 hours is in the first quarter.