NAHRIM PUBLICATIONS

RESEARCH ON SIMULATION OF THE IMPACT OF CLIMATE CHANGE ON RIVER EQUILIBRIUM MORPHOLOGY IN THE PADAS RIVER BASIN, SABAH

  Report   River Basin

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Author
Ir. Ts. Gs. Dr. Safari Bin Hj. Mat Desa, Ir Liew Yuk San, Mr. Mohd Afzaihelmi Bin Mohd Ariff

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Anthropogenic activities such as deforestation, urbanization, plantation agriculture, logging, and sand mining are well-established drivers of river system degradation and ecological imbalance within river basins. These activities have disrupted natural river flows and significantly altered land cover, adversely impacting both environmental conditions and local ecosystems. This study examines the impacts of land use changes and climate change on river equilibrium morphology in the Sungai Padas basin. The research involved developing digital maps to model storm events for 48- hour critical storm durations across 2-, 5-, 10-, 20-, 50-, 100-, and 1000-year Average Recurrence Intervals (ARI), considering both current and future land use changes (Scenarios 1a and 1b). Additionally, scenarios incorporating a Climate Change Factor (CCF) were assessed for the 2-, 5-, 10-, 20-, 50-, and 100-year ARIs for the Sungai Padas basin (Scenarios 2 and 3). The HEC-HMS model was employed to generate runoff hydrographs that reflect the effects of land use and climate change, while HECRAS was used to develop a hydraulic model simulating open channel and overbank flows under unsteady conditions, resulting in flood inundation maps. Sediment sampling conducted in September and December 2020 from five sites along Sungai Padas identified average bed material sizes (d50) ranging from 0.20 to 0.31 mm, classifying the river as a medium sand-bed system. Sediment rating curves were developed for three locations along Sungai Padas, based on total sediment load and discharge (Q) measurements. Furthermore, a hydrodynamic sediment transport model using Yang’s unit stream power function (1973) was developed to simulate channel-bed profile changes and identify areas of sedimentation and erosion along Sungai Padas and Sungai Pegalan. The simulation indicated a maximum sediment deposition of 5.59 m and erosion of 5.00 m following storm events. In total, 26 digital maps were produced, highlighting changes in bed elevation and potential locations for bank erosion. The simulation results for all scenarios (1a, 1b, 2, and 3) consistently identified bank erosion at the same locations. Based on these findings, a strategic approach to erosion and sediment control in response to land use changes and climate change impacts has been proposed. The management and development plans include eight action plans aimed at minimizing the effects of erosion and sedimentation to achieve sediment equilibrium for the Sungai Padas basin.