Application of Grey Theory Rainfall - Runoff Modeling for Years of Data Lacking(Case Study: Shahrchay Watershed, Urmia)

Flood estimation in a watershed with little statistic data is of interest for hydrologists، specially in developing countries. Noting the importance of this subject، the ability of Grey theory in flood estimation was investigated in Shahrchay watershed for the years without statistic data. The model was verified by assuming two different cases in the studied watershed. In the first case، on the basis of recorded rainfall and limnograph data for all of the occurred rainfall events، different alternatives were used for the model verification. In the second case، by assuming lack of recorded rainfall gauge data in two selected years، the model verification was evaluated. In this case، hourly precipitation pattern of accumulated rainfall gauge data were estimated by three methods namely world meteorological organization (WMO) method، local amounts of WMO method and the equation presented by Ghahraman & Abkhezr. The results showed that the Grey theory was very sensitive to the actual data and the recorded rainfall gauge data played an important role in estimation of this theory parameters and consequently the Grey theory could correctly simulate the discharge values. The results also showed that WMO method had high ability in flood hydrographs prediction than local and Ghahraman & Abkhezr methods and Ghahraman & Abkhezr method with average relative flood volume variation of 12. 5 %، had the most ability in flood volume prediction in comparison to WMO and local methods.