EFFECT OF HISTORICAL FLOODS ON ESTIMATION OF LARGE DAMS DESIGN FLOODS

The statistics and data observation of maximum floods recorded at dam site are a major determinant of design floods assessment. For this purpose, the accuracy and correctness of data shall first be insured prior to any calculations and then the weight and value of any quantity recorded shall be scrutinized as dimensions of events within the scope of time in question, and where applicable, the position thereof shall be determined. However, in some cases, the value and position of recorded statistics are not cared about and all information are considered to have the same value. Then, the floods as well as different return periods thereof are assessed applying the common techniques. As a result, there will be no compatibility between the firgures obtained for design floods and catchment area under study. Therefore, great expenses spared for construction of huge concrete structures considering these floods may be likened to a large amount of premium, which would be paid for imaginary events that will never happen. In this investigation, at the beginning, the watershed area of Kuran-Buzan Dam on Seimareh river was selected as the scope of study and the historical floods occurred were distinguished from other floods (systematic series) gauged at hydrometric station through method of US Water Resources council afterwards. The mentioned floods were thence combined through a method offered by the Committee and then obtaining the required statistical parameters, design floods of Kuran-Buzan Dam were adjusted. Therefore, in case the historical floods are recorded at dam site or neighboring stations, this method can be applied for estimation and adjustment of large dams design floods.