Morphology and channel characteristics of an equatorial tropical river in Malaysian Borneo: a detailed evaluation through spatially explicit geomorphometric modelling

Abstract

Geomorphic and morphodynamic characteristics of Akah River in Sarawak, Malaysia in north-western Borneo were modelled using geographical information system assisted techniques and geomorphometric indices. Stream properties such as longitudinal profile, stream length gradient index (SL), channel slope, hypsometric curve, hypsometric integral, sinuosity index and channel cross profiles were analyzed. Morphological features such as meander and channel bar characteristics were evaluated and compared to classify the river and to identify the processes responsible for its present nature. The longitudinal profile, SL index and channel slope indicate the presence of multiple knick points in the channel, which may be indicative of changes in the base level characteristics of the river or lithological differences. The characteristic convex shape of hypsometric toe indicates late stage of deposition due to diffusive processes and the hypsometric integral identifies the geomorphic evolution as in the advanced stage i.e. erosion is significant. The sinuosity index classifies the entire river as meandering and some segments as tortuously meandering with varied stream valleys. Numerous channel bars of various dimensions are found in different reaches of the stream indicating varying channel bottom characteristics and flow mechanism due to the influence of geological process. The information generated from spatial modelling of different geomorphic indices (different terrain variables) and channel characteristics classifies the Akah subwatershed with slope (diffusive) and fluvial dominated geomorphic process having highly meandering channel and showing anomalous characteristics in some segments. These findings will serve as baseline information, while considering the region for hydrological development activities which include check dams, mini hydroelectric projects.