Geospatial mapping of flood susceptibility and hydro-geomorphic response to the floods in Ulhas basin, India

Flood is a common natural disaster that causes immense damage to the natural environment, construction and casualties every year around the world. The effectiveness of flood is a function of several criterions such flood power, magnitude, frequency, duration of the flow, changes of the planform and cross-section geometry in a river etc. Alternatively, the prevention of flood depends on assessment of various factors which are related to flood occurrence. In an international scale, it may not be possible to prevent flooding by some full scale assessment of environmental factors. However, deterrence of regional floods can easily be done through flood susceptibility mapping. The present work represents an innovative analysis of flood mapping through the analytical hierarchy process (AHP) and hydro-geomorphic response to the floods by implementing geospatial analysis and unit stream power modelling. The subject field is applied in Ulhas catchment, India. The hydrologic assessment of yearly peak discharge shows that the hydro-station located at Badlapur is capable to transport upto 0.5 m boulder during extreme flood events. However, there is no transformation of the cross-section geometry during 2005–2012 at Badlapur. The flood susceptibility map is constructed based on twelve influencing parameters, i.e. elevation, slope, distance from drainage network, geomorphology, drainage density, flow accumulation, rainfall, land-use, geology, stream power index, topographic wetness index and curvature of the topography. Established along the resultant flood susceptibility map, it is found that about 25% area of the Ulhas catchment is under very high flood susceptibility. The efficiency of the analytical hierarchy process is examined by employing area under the curve (AUC) method which shows considerable accuracy (84%). The present study bridges the gap between the hydro-geomorphic assessment of the flood and the geospatial approach towards flood susceptibility.