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ABSTRACT
Effect of rapid urbanization has accelerated the impact on the
catchment hydrology and geomorphology. Such rapid development which
takes place in river catchment areas will result in higher sediment
yield and it will not only affects river morphology, but also river
channel stability, causing serious damages to hydraulic structures
along the river and also becoming the main cause for serious
flooding in urban areas. Therefore, it is necessary to predict and
evaluate the river channel stability due to the existing and future
developments. This study was carried out at Sungai Kulim in Kedah
state, Malaysia, by means of evaluation on sediment transport using
recently observed data up to year 2006. The present study attempts
to give an overview of the channel changes and sediment transport
phenomena in Sungai Kulim. A total of 24 samples of bed materials
were collected from four locations (CH 20000, CH 14390, CH 3014 and
CH 0), and 14 river hydraulics and sediment transport data sets
including discharge, bed load, suspended load and total load were
collected from two locations (CH 14390 and CH 3014) from 2004 to
2006. The data were used to analyze and evaluate existing Manning
equations and sediment transport equations. Attempts were also made
to derive new Manning equations (Equations 4.3 and 4.4) with a
correlation coefficient, R2 = 0.86 for application to the
moderate-size channels in Malaysia. The results of evaluation for
total load equations at the two locations along Sungai Kulim show
that Engelund & Hansen equation gave the best prediction for sand
bed stream and yielded highest percentage of data with discrepancy
ratio in between 0.5 and 2.0 (33.33% at CH 14390 and 62.50% at CH
3014). An erodible-boundary model, FLUVIAL-12 which simulates
inter-related changes in channel-bed profile, width variation and
changes in bed topography was selected for this study.
Engelund-Hansen equation and roughness coefficient, n = 0.030 were
selected for the model which was calibrated and validated for water
surface profile and bed elevation. The comparison of the surveyed
river geometry data in September 1991 and field measurements from
October 2004 to November 2006 shows that there has been a change in
cross section after several flood occurrences from 1991 to 2003. The
predicted bed levels by FLUVIAL-12 were almost similar to the
observed bed level from 2004 to 2006, this confirmed that channel
bed degradation occurred along the 14.4 km study reach. The model
simulation results for existing conditions, future conditions and
long-term modeling show that the sediment size and channel geometry
in Sungai Kulim changed significantly. However, modeled results show
that future changes in cross sectional geometry will be limited and
erosion along the reach will slow down from 2006 to 2016, thus
Sungai Kulim was predicted to be stable at most locations.
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