The morphology of a river channel is driven by multiple forcing factors that can be either external or internal. The internal factors, such as the variation in rock strength, lineament orientation, and fracture density can be an impelling force in the landscape evolution of a slow uplifting terrain. The spatial variation in the internal factors may result in heterogeneity in fluvial erosion rates, which may produce false signals of active tectonics in a terrain. The Himalayan orogeny has resulted in an upward flexure in the Indian crust known as a peripheral forebulge. The uplifted Vindhayan plateau is proposed as the depiction of this flexure. The bending of the Indian plate has resulted in the generation of tensile forces in this area. These forces have resulted in the formation of large-scale lineaments, which are roughly aligned parallel to the axial plane of the forebulge. This study highlights the role of lineaments, rock strength, and fluvial erodibility in the tectonics of forebulge. We used N-type Schmidt hammer to measure the intact rock strength of lithologies met in the Vindhayan plateau. We calculated the Normalized steepness index (Ksn) to assess the fluvial erodibility of the channels. We calculated swath profiles and local relief distribution to understand topographic variation. Further, we looked at the knickpoint distribution and tried to correlate it with major lineaments and lithological boundaries. Finally, we tried to understand the relationship between the lineament distribution and regional tectonics of the forebulge. We find that there is a significant difference in fluvial erodibility between the weakest and strongest lithologies. We observed that the lineaments act as the conduits for rapid erosion and knickpoint formation. The Ksn values are relatively high where we encountered the hard lithologies, resulting in the formation of vertical knickpoints (waterfalls). We have observed a correlation between, Rock strength variation, topographic relief, knickpoints, and Normalized steepness index. Our results suggest that spatial variation in rock strength and lineament pattern is playing a crucial role in the landscape evolution of the Vindhayan plateau. We finally propose a model to relate lineament orientations and lithological variations with slow uplift of the forebulge.

Hillslopes are responsible for the production and transport of sediments within a landscape (Gilbert 1877). Since the hillslope gradient and morphology tend to vary across a landscape, it is expected that the erosion and sediment delivery would also be non-uniform. In this study, we explore the probability of the flux at a particular point in the catchment reaching the river mouth using connectivity and the Revised Universal Soil Loss Equation (RUSLE) in the Pranmati river catchment (a small 3rd order Himalayan river catchment within the Ganga River system). Methodology involves characterising the hillslopes of Pranmati river catchment centered on land use and land cover units. Using RUSLE, the sediment yielding capacity of various land cover units are estimated based on which potential source areas are marked. The sediment connectivity within the basin is also calculated by generating a sediment connectivity map of the area using method given by Borcelli et al. (2008). The catchment is categorized into four classes – (A) Highly connected zones with high sediment yielding capacity (B) highly connected zones but low yielding capacity (C) poorly connected zones but high yielding capacity (D) poorly connected zones and low yielding capacity. The area is then mapped on the basis of the defined classes and potential areas of erosion and storage are identified. Our results show that about 62% of the catchment area has low connectivity implying sediment flux generated in these zones have a low probability of leaving the catchment. Only 11% of the catchment area has sediment yield greater than the mean yield per hectare. The sediment generated from this small area of the catchment contributes 93% of the total sediment production of the catchment. References Borselli, L., Cassi, P., & Torri, D. (2008). Prolegomena to sediment and flow connectivity in the landscape: a GIS and field numerical assessment. Catena, 75(3), 268-277. Gilbert, G. K. (1877). Geology of the Henry mountains (pp. i-160). Government Printing Office.