A method for derivation of flood peak profile along stream networks based on transposition of regional models using GIS

Damages caused by floods are one of the most important concerns of the people Living on the flooding inundated regions. Flood damages constitute a large Fraction pf total damages due to natural disasters in Iran, especially during recent years. For design of hydraulic structures, watershed management operations, setting insurance policies and locating suitable places for designing facilities in the future require knowledge of flood peak values. A requirement for flood mitigation is to estimate spatial variations of flood discharge in main streams for different return periods. Since flood regional analysis is based on available data collected at hydrometric stations, the main objective of this research is to generalize results continuously from gauged stations to all points located along the stream network. In this study, geographical information system (GIS) is used to apply regional relationships and provide flood discharge profile (discharge variations versus distance) and present digital flood maps. As spatial variations of hydro-geomorphic indices in a basin such as area, slop precipitation, and vegetation affect flood peak discharge, advanced GIS techniques are capable of calculating spatial distribution of indices and regionalize relationships in stream network so as to access the flood discharge variations. In this study, spatial generalization methods were applied for watersheds located in north of Iran, called wester-khazar region, as a part of Caspian Sea basin. Flood regional analysis resulted in multivariate regression relationships which indicated that parameters such as area, main stream length and annual precipitation are the most effective factors in selected models for different return periods. To map peak discharge, it is imperative to have rasterized maps of main hydro-geomorphic indices such as flow accumulation, flow direction, flow length and stream network derived from the DEM. The comparison Of observed and estimated values in selected network locations showed that this method has high efficiency and also is a powerful method for peak discharge estimation in the region. Furthermore, the results of research can be used to delineate flood based maps and other necessary criteria for design of hydraulic structure and flood control projects. Key words: Flood regional Analysis, GIS, Flow Direction, Flow Accumulation, DEM