SALINITY INTRUSION MODELLING FOR THE LOCATION OF A WATER SUPPLY INTAKE ON THE KEMENA RIVER, SARAWAK

摘要

Evaluation of the Kemena River as a water supply source required measurement of flows, water levels, and salinities under drought conditions, survey of river cross sections, hydrological and hydraulic modelling, and salinity modelling. The flow may be stratified or well-mixed, depending mainly on the freshwater inflows. Salinity intrusion was modelled for the well-mixed case using MIKE 11, and was estimated for the stratified case from an experimental study of the mechanism and shape of the arrested saline wedge. As there was no network of level benchmarks extending up the river, the hydraulic model was used, with recorded tidal water level variation at several points, to define the horizontal surface in the tidal reaches. The freshwater inflows for the calibration and design simulations were estimated by hydrological modeling. The hydrological model simulates seven different types of natural storage and the flows between them, and includes kinematic wave routing of flows along the channels. The hydrological model was calibrated using long term flow records for a small tributary of the Kemena, and short term flow records for one of the headwater subcatchments of the Kemena. Freshwater inflows for the calibration simulations were calculated from the rainfall records for that period. The design freshwater inflows were determined by running the calibrated hydrological model for an extended period, using rainfall and evaporation data as input, and performing frequency analysis on the resulting flows.