Modelling spatial variation in erosional status and geomorphic evolution of the Limbang river basin in Northern Borneo through hypsometric analysis

Erosional status and geomorphic evolutional stages of the Limbang River Basin (LRB) and its fifteen subwatersheds were investigated in the present research through analysis of hypsometric curve characteristics. Spatial analysis of topographic parameters (elevation, slope and relative relief), shows differential and varying proneness of the subwatersheds to erosion. Hypsometric curve parameters like hypsometric integral (Ea), maximum concavity (Eh), coordinates (a*, h*) of the curve-slope inflection point (I), and normalized heights of the hypsometric curve at 20%, 50%, 80% and 90% of the area revealed similar characteristics of the subwatersheds with more detailed information about its spatial variation. Hypsometric curves showed dominance of concave, convex and mixed concavo–convex shapes in spatial-proximity with integral values indicating an almost equal number of subwatersheds (seven) with old (Ea <0.30) and (eight) mature (Ea >0.30) stages of geomorphic evolution. Parameters such as concavity, slope inflection point, normalized hypsometric curve height at various points revealed varying level of influence of fluvial and diffusive processes in terrain erosion and subwatershed characteristics. Further, subwatersheds with varying Ea and Eh signifies the role of varying lithology to the tectonic processes operated in the region. Spatial variation of lithology in proximity and its differential response to the tectonic processes has induced the variation in erosional characteristics and thus controlled the geomorphic evolutional stages of the subwatersheds in LRB.