The Study of Paleoflood Hydrology Using Slack-water Deposits(Case Study: Darungar Basin)

Palaeoflood hydrology is the reconstruction of the magnitude and frequency of recent, past, or ancient floods using geological evidences (Baker et al., 2002). The term "palaeo" has contributed to the general misconception that palaeoflood techniques are only used for estimating very old floods over geological timescales. However, most palaeoflood studies involve the study of the last 5000 years with an emphasis on the last millennium, or even the last100 years in ungauged basins (Benito et al., 2005).J. Harlem Bretz (Bretz, 1929) was the first scientist to use geological evidence intensively to elucidate information about past floods during his studies of the pathways followed by the cataclysmic outburst floods from Pleistocene Lake Missoula. However, the term and concepts of palaeoflood hydrology were formally introduced by Kochel and Baker (1982). They emphasized on slack-water deposits (SWD) and palaeostage indicators (PSI) as geological, geomorphological and geobotanical evidences for reconstruction of ancient floods. These indicators represent the high stage of the flood and provide the best natural record of large flood magnitude. Slak-water deposit sites include back-flooded tributary mouths, caves and alcoves in canyon walls, channel expansions where flow separation causes eddies, and overbank floodplain deposits. Ideal palaeoflood sites preserve multiple flood stratigraphic records, which can be separated into individual flow events using sedimentological criteria (Baker, 1987; Benito et al., 2003).