Palaeoflood Hydrology in the Indian Context

Flooding m monsoon-fed rivers profoundly challenges flood hazard management because of large spatio-temporal variability m the monsoon rainfall over the Indian region and scarcity of long-term hydrological data Under such circumstances, pre-instrumental (recent, historic or pre-historic) records of large floods could be reconstructed by using palaeoflood hydrological techniques This paper briefly describes the methodology adopted to reconstruct longterm flood chronologies (over centuries to millennia) using geological and geomorphological evidence, and summarizes the results of palaeoflood studies on eight Indian nvers undertaken during the last two decades The paper also briefly discusses the potential for palaeoflood hydrological studies in different hydro-geomorphic regions of India and the future prospects of palaeoflood hydrological investigations in India for flood-risk assessment of both gauged and ungauged nvers Three conclusions are possible concerning palaeoflood archives m India (a) the palaeoflood records generally span a time period of 1-2 millennia, (b) the post-1950 floods were observed to be the largest at least dunng the last several hundred years, indicating increase in both the magnitude and frequency of large floods m recent decades, and (c) the period between ca W and 19'' century AD was marked by a sharp decline in the frequency of large-magnitude floods on all rivers, suggesting a palaeochmatologic cause This distinct period of low monsoon floods approximately coincides with the Little Ice Age, a global climatic phenomenon In a country like India, where there is paucity of long-term hydrological data, palaeoflood records are a great source of potential information that could play a critical role in formulating design decisions for different types of engineering projects as well as water resource development projects on both ungauged as well as gauged rivers.