Model Assessment of Water Quality in Sarawak River, Malaysia

Kuching City as the state capital of Sarawak is one of the most developed urbanisation township in Malaysia. It is located at the downstream part of the Sarawak River basin with an area of 1,700 km(2). The river basin in particular the Kuching City and its adjacent areas have been experienced frequent floods causing hardships to the local population and significant damages to the economy. In addition, it has been observed that river environment and water quality was also deteriorated. To overcome these problems, the Government of Malaysia has been taken the initiative to carry out the major infrastructural works to alleviate the flood in the river basin. The flood mitigation works for Kuching City have proposed numbers of structural measures within the Sarawak River basin in order to protect the city against the flooding. Tidal control gates, bypass channels, river barrages and causeways are among the major solutions that have been considered to mitigate the overspill of storm water from Sarawak River to the city area. However, the occurrence of severe storm is not frequently happened in a year and the operation of tidal control gates in most of the time is closed. Therefore the capacity of flushing within the system will be an issue and phenomenon of stagnant water within the bypass channels will contribute to the deterioration of river water quality. The assessment of river water quality was carried out by simulating the numerical model for a few calibrated scenarios. The simulations also cover the future conditions of Sarawak River with proposed structural measures and various modes of system operations. Finally, current river water quality status was determined and the optimum duration for flushing in bypass channel to maintain healthy river water quality was recommended.