- Type of project
- Location
- Malaysia
- Continent
- Asia
- Company
- Alkyon Hydraulic Consultancy & Research
- Client
- National Hydraulic Research Institute of Malaysia (NAHRIM)
- Period
- March 2007 - May 2008
- Contract value
- Objective
The objective of the research was to stimulate the hydrodynamic behaviour of the Selangor Estuary at the Malaysian west coast by utilizing a 3D numerical model (Delft3D) and to assess the impact of water extraction for the salt levels in the estuary.
Project information
The west coast of the Malaysian Peninsula is an area which has developed rapidly over the past decades. The centre of this development is the Malaysian capital Kuala Lumpur and, along with the growth in population and wealth, the demand for fresh water has risen. To fulfil this demand the Malaysian authorities constructed infrastructure to extract water from the Selangor River. This river is preserved from large scale pollution, in contradiction to most rivers in the industrial area around Kuala Lumpur. Nowadays more than half of the river discharge is transported as drinking water to Kuala Lumpur. This meant a significant change in the river regime in the downstream stretch of river. The stretch of river near the mouth hosts a valuable ecosystem, with a unique population of synchronous flashing fireflies. These creatures attract many visitors and are the driving force behind the local tourism industry. The part of the river where they live is influenced by the tide and the river discharge. The concern is that the decreasing river discharge will cause the saline sea water to penetrate further upstream. The ecosystem with the fireflies is sensitive for salinity and the decline in the population of fireflies in the last decade is blamed by some to the water extraction upstream.
Description of project
This study used the numerical modelling software Delft3D to simulate the hydrodynamic behaviour, including salinity, of the downstream part of the Selangor River and assess how the decrease in discharge affects this part of the river. The hydrodynamic behaviour in estuaries is determined by the fluvial regime and the tide-dominated marine regime. For the generation of boundary conditions for the Selangor Estuary Model a 2-dimensional flow model of the coastal zone is created. The point of departure was an existing large scale tidal flow model covering all coastal waters surrounding Malaysia. This large scale model appeared to be too coarse and inaccurate for direct derivation of boundary conditions. Two steps of refinement and optimization are applied, which resulted in the Malacca Strait Model and the Northern Approach Model. These models are both forced by astronomical constituents and calibrated with known, observed constituents. A calibration technique was developed which optimizes the boundary conditions for each partial wave. Secondly the propagation and shoaling of the partial waves is analyzed and the model setup was optimized based on these results.
The results of the most refined Northern Approach Model were used as boundary conditions for a detailed, 3-dimensional model of the Selangor Estuary. Water levels and flow velocities were combined in a Riemann boundary to obtain the highest accuracy. Density induced flow is controlled by salinity only. To capture the dynamic process of salt intrusion a stable situation is assumed for most conditions. To simulate this process one tidal cycle is selected and restarted with the results at the end of the former simulation, until model results are stabilized. The Selangor Estuary Model is calibrated and validated with water levels, flow velocity and salinity and showed good results. Salinity was predicted within a range of a few ppt and stratification was also in accordance with the observations. The validated model is used to assess the impact of the water extraction in the river. The required base flow in the Selangor River is 3.5 m3/s, while before water extraction the average dry season discharge was 30 m3/s. This results in the maximum salt limit of 6.5 ppt at the surface to advance 3.4 kilometres further upstream for an average tidal range. A constant salinity of 6.5 is known to be harmful for the ecosystem. Further research should clarify the effects of variable salt levels and what the role of the salt intrusion is in the downgrade of the firefly population.
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