River bank erosion is one of the major and unpredictable hazards worldwide including in Malaysia. Soil detachment at river banks is due to two processes: 1) hydraulic erosion imposed by channel flow and 2) sub aerial erosion due to the weakening and weathering of bank materials. This paper is focused on the second aspect of the erosion process which mainly depends on the combination of rainfall intensity and the ability of the soil to withstand the raindrop effects. The relative combination of sand, silt and clay in a soil is argued to have an impact on erosion resistance. In cohesive soil composition, sand forms the largest size ranging from 0.05 to 2 mm whereas silt is adequately moderate (ranging from 0.002 to 0.05 mm) and clay is the smallest of all three (less than 0.002 mm). With the knowledge that soil composition does indeed have an effect on erosion resistance, this paper will attempt to relate risk assessment index of river bank erosion specifically to soil composition. Thus, the objectives of this document are as follows; 1) to produce risk assessment index for river bank erosion and 2) to carry out a case study for selected rivers in Malaysia pertaining to river bank assessment. The index is produced by inferring the previously developed scale on soil erodibility. Past researchers created the “ROM” scale (named after the researchers, Rolan and Mazidah) to assess degree of soil erodibility into five classes namely “critical”, “very high”, “high”, “medium” and “low”. Instead of using semi empirical formula from the “ROM” scale, a percentage of soil composition was inferred to produce risk assessment index. It was found that as the percentage of clay decreased, susceptibility index became higher and approached a critical level. Application of the newly developed index is verified by conducting a case study at the Langat River, Kajang, Malaysia. The soil composition was classified and form fitted into the index. It was found that the middle reach of the Langat river is susceptible to severe erosion due to low percentage of clay. This finding agreed well with the visual observation of these reaches as a large portion of gully type of erosion had been observed throughout the study. The establishment of risk assessment index which firmly indicates the relationship between soil composition and river bank erosion can be used as a tool in forecasting the risk levels. This formulation is well proven to assess river bank conditions and the associated critical shear stress is very much close with the previously published shear stress

Predicting sediment transport in a river system is necessary when attempting to monitor river changes due to incoming particle deposition from upstream reaches. Previous studies have used various techniques such as probabilistic, regression, and equal mobility approaches to make predictions. However, issues associated with multicollinearity occur when using the regression approach. Significant correlations between the explanatory variables in a regression equation can increase the coefficient variance estimates, which make these estimates very sensitive to minor changes. Thus, we propose the use of principal component analysis as a solution to these issues. We observed that the variance inflation factor is less than 10, which indicates the nonexistence of issues associated with multicollinearity. Fitting components to the regression equation create a new prediction model for sediment transport, which improves upon previous equations using the same technique.

Acoustic Doppler Velocimeter (ADV) has become prominent device in flow and turbulence measurement. The in situ turbulence measurement requires laboratory-quality data to be obtained in the field. Thus, ADV vector type provides a better choice for flow measurement at field scale. A field study was undertaken at sand-gravel bed rivers to observe the flow field and turbulence characteristics in the presence of protuberant clast. Profile measurements were executed at near bed region to characterize the flow and turbulence characteristics at the proximity of clast reference. Four major areas were identified as sampling location relative to clast reference namely stoss side, adjacent area, wake area and the downstream area. Besides, bed load measurement was carried out concurrently to elucidate the possible relation between flow variation and transport rates. Physical meaning of flow field is expressed in term of mean velocity, turbulent intensity, turbulent kinetic energy, Reynolds stresses and horizontal-vertical interaction, local bed shear stress and quadrant analysis. It is postulated that the presence of protuberant clast modifies flow field and affect transport rates. Possible occurrences of transport rates are subject to accurate estimation of acting forces on moving particles. Estimation of critical Shields stress from Reynolds extrapolation provides better comparison with actual transport rates. Besides, contribution rate to Reynolds stress analysis compliment the importance of sweeps and ejection events to occurrence of bed load transport.