MORPHODYNAMICS AND FLOOD HAZARD ASSESSMENT IN THE TAWI RIVER USING MULTI-CRITERIA DECISION ANALYSIS

The Tawi River draining through the city of Jammu in northern Himalaya is fluvially highly dynamic and has been undergoing rapid morphological changes. This region has a long history of flooding worsened by rapid anthropogenic interventions in recent times. The Tawi river exits the mountains near Jammu city and disperses into alluvial plains. The river develops two anabranches, called Nikki Tawi and Waddi Tawi, downstream of Jammu, which rejoins after flowing independently for ~20 km. Both anabranches exhibit significant channel dynamics and severe aggradation at sub-reach scale, marked as ‘hotspots.’ Our analysis shows a continuous reduction in active flood plain and channel belt width since 1968. Among 17 Sub Reaches (SR’s), SR 5 and 6 are identified as hotspots of siltation and dynamics and show maximum decrement of the bar area (6.39 km²) and channel belt area (6.88 km²), respectively. Floodplain encroachments lead to nearly 50% reduction in the channel belt of the Tawi river in several SR’s since 1968, restricting the river to flow into a narrow path and creating severe flood conditions. We used a series of morphometric parameters such as channel slope, bar area/channel area ratio, center-line shift, sinuosity, distance from tributary confluence, floodplain development, and active floodplain width, which were integrated using multi-criteria decision analysis and identified SR 3, 5, 6, 13, 14 and 17 to be at very high and high risk of flooding. We also note significant anthropogenic factors contributing to increased flood risk in recent years, and these include construction of embankments and human settlements within the historic channel belt, continued reduction of the active floodplain, close spacings of bridges, and an artificial lake project. Our assessment suggests that the incorporation of channel morphometric parameters is critical for flood hazard assessment in the Himalayan rivers. We strongly recommend ‘soft engineering’ solutions such as protecting ‘river space’ and promoting land-use regulations for sustainable flood management in this region.