خالد اوسطی

Knowledge of rainfall-runoff relationship is one of the most important subjects in hydrology, watershed management, water resource and etc. Hydrograph is effective way to study floods. Derivations of the unit hydrograph from complex storms can be effective in compensate ideal event shortage and calculating an exact unit hydrograph, although it’s complicated calculations. Differences of complex storms and single storms in base flow separation and excess rainfall calculations are discussed. This paper also discusses about a common mistake in unit hydrograph derivation studies, i.e. using “matrix method” instead of “least square method “. Least square method is a method derived from matrix method and is based on rainfall-runoff relationship mathematic basics and simultaneously solution a set of equation derived from Convolution equation, as noted in performed studies. Both LP and least square methods are the best method to derivation the unit hydrograph from complex storms but matrix method is less effective than least square method.