Geomorphic and Ecological Assessment of Lower Silai Corridor for Stream Restoration

Abstract

The increased intensity of anthropogenic activities, which are mostly concentrated within river corridors, has altered the natural functioning of fluvial systems beyond their regeneration capacity. Therefore, much attention has devolved towards riparian zone conservation and management using integrated hydromorphological approaches for sustaining the overall river health. While such approaches have been adopted for various basins worldwide, they have seldom been applied to Indian rivers, particularly in West Bengal. In this study, the Silai River Basin, which encompasses part of the eastern fringe of the Chotanagpur Plateau in Puruliya and the alluvial plains of Bankura and Paschim Medinipur Districts in West Bengal, has been analysed to ascertain the efficacy of bioengineering solutions in mitigating the common fluvial/anthropogenic hazards prevalent in its riparian zone towards restoring the stream's hydromorphological health. The overall reach-wise ecogeomorphic character of the river and its present health status has been examined using multi-metric indices that seek to assess river health based on the channel's morphological, hydrological and ecological functionality, highlighting sites that are impaired and commonly afflicted by hazards such as floods and riverbank erosion, sand mining activities and consequent soil loss and land degradation. A detailed analysis of these hazards enable pinpointing of sites where possible bioengineering solutions (live grass buffers) can mitigate the ambient river health degradation. The effectiveness of Vetiver grass (Vetiveria zizanioides) as a soil and water conservation tool is investigated along the River Ketia, a spillchannel of the Silai River, to gauge the impacts of this grass' root network on those soil physicochemical properties that contribute towards increased soil cohesion and slope stabilisation. The performed 1-D simulation modelling to examine the effect of the grass' aboveground biomass in reducing flood velocities and retarding excess overland flow also yielded positive results. Therefore, installing these grass buffers along bare, eroded slopes that are affected by soil loss, can become a viable solution to reduce the volume of overland flow and sediments reaching the channel, helping to lessen flooding in the region. Hence such environment-friendly and cost-effective grass buffers can become sustainable riparian conservation tools to restore the already much degraded river basins across India.