River space: A hydro-bio-geomorphic framework for sustainable river-floodplain management.

The lateral dimension of an alluvial river - floodplains - provides a plethora of goods and services for human needs. Also, it supports the richest and diverse riverine ecosystems on Earth. But over-utilization of floodplain resources had impacted functions of river system adversely. So, the present study attempts to formulate a hydro-bio-geomorphological framework to assess the lateral dimension of a river system for sustainable management of river-floodplains and termed as river space in this paper. The study illustrates river space at seven hydro-meteorological sites situated on the main stem of the Ganga river in the ~750 km stretch that lies between Haridwar and Prayagraj cities. For hydrological aspect, the flood frequency analysis is used to identify flood inundation widths for floods of different return periods with the help of the rating curve and derived cross-section from satellite imagery. Bio-geomorphological aspects are taken into consideration for corroborating the hydrologically assessed river widths (lateral dimension). The present study suggests that the minimum river space should be equal to the lateral width corresponding to the 1-year return period flood. In the present hydro-meteorological sites in the middle Ganga plains, it ranges from 2 to 21 km. Overall, the present study gives an insight of a simple and logical approach that could be beneficial for the biomic restoration of rivers and their floodplains.