Conservation and Restoration of Urban Rivers : Case Studies of Raia River and Pari River
As a result of increasing economic growth of the country, areas within river catchment are being developed for commercial, industrial and housing purposes. Effect of this rapid urbanization has accelerated impact on the catchment hydrology and geomorphology. These developments have caused dramatic increase in the surface runoff and the behavior of sediment output, hence resulting in higher sediment yield.
Since any flood mitigation works would likely involve channel modification, so knowledge of predicting the geometry changes as a result of sediment transport movement is significant and necessary. By using appropriate method, channel stability and river equilibrium can be achieved.
Intensive literature review has been made on several aspect of river morphology such as characteristics of natural river, channelization works and their impact, and conservation concept toward restoration of channelized river.
Two catchments namely Raia River at Simpang Pulai, Ipoh and Pari River at Ipoh, with different land use and development were chosen for this study. Raia River represents a natural river while Pari River represents a channelized river.
Several gauging stations were identified based upon the river characteristics such as straight reach and bend. Six stations for Raia River and four stations for Pari River were selected. Sediment sizes were identified by collecting bed and bank materials from each station. Surveys of existing cross section and water level measurements were carried out for comparison purposes with the morphological changes predicted by FLUVIAL-12 and three different method of designing stable channel.
Comparisons on the three empirical design methods including maximum velocity, tractive force and regime method (Simons and Albertson, 1960) with mathematical model (FLUVIAL-12) using field’s data were carried out in order to choose the appropriate method which will minimize the morphological changes in river channel. The results from the mathematical model (FLUVIAL-12) that comprises component of water and sediment routing, indicates channel changes that agrees well with the characteristics of a dynamic river. FLUVIAL-12 is also capable of predicting channel instability effect such as erosion and sedimentation at straight reach and bend for both Raia and Pari River.
Simulation results based upon FLUVIAL-12 also indicate that Raia River can be conserved as a natural river by maintaining cross section with a side slope of 1:2. By ensuring the Manning’s roughness coefficient to be 0.025 and a cross section with a side slope of 1:2, Pari River can be restored as a natural river without the concrete bank.