Connectivity structure of the Kosi megafan and role of rail-road transport network

• Anthropogenic impacts over the Kosi megafan analysed in a GIS framework.
• 2-D connectivity structure defined by longitudinal and lateral connectivity.
• Rail/road network significantly impacted the connectivity structure&sediment flux.
• Disconnectivity over the megafan resulted indrainage congestion and waterlogging.

Movement of biophysical fluxes and resultant processes are governed by among other things, the (dis)connectivity structure of a landform. Hence, the quantification of connectivity structure of a landform is important in order to analyze water and sediment fluxes over a surface. Two dimensional connectivity structure through analysis of lateral and longitudinal connectivity for water and sediment flux has been quantitatively defined for the well-known Kosi megafan in north India. The avulsive behavior of the Kosi River has resulted in various paleochannels over the megafan, and they guide the flux transfer over the surface and also control the local topography of the megafan. As (dis)connectivity structure of landform is governed by its physical characteristics and also affected by anthropogenic disturbances, both these factors have been considered to quantitatively analyze the connectivity structure of the Kosi megafan for sediment and water fluxes. Megafan surface characteristics have been defined through local slope variability, land use-land cover map and flow length. These surface parameters have been used to map ‘buffers’ in the area. The distribution pattern of ‘buffers’ on the megafan surface has been used to define the ‘natural’ (dis)connectivity structure. Further, the megafan surface has also been affected by progressive development of the rail-road transport network, which is mostly east-west aligned and intersects the south flowing paleochannels. These rail-road network acts as an anthropogenic ‘barrier’ for water and sediment fluxes across the megafan surface. A detailed mapping of rail and road network in different years (1955, 1983 and 2010) has been used to characterize anthropogenic disturbance on the connectivity structure. The spatio-temporal variation in connectivity structure is attributed to density of the transport network. Finally, natural and anthropogenic disturbances on connectivity structure have also been integrated to quantitatively define the present day connectivity structure of the Kosi megafan for water as well as for sediment flux. Further, the (dis)connectivity structure has been used to explain the spatial variability of waterlogging over the megafan surface, which is presently a serious hazard in the region.