ABSTRACT
Riverbank erosion and lateral migration changes are very complex and complicated processes. Although it is obvious that all rivers will experience these phenomena, it may be less obvious that there are consistent underlying relationships between different riverbank erosion and lateral migration with parameters such as hydraulic and hydrodynamic characteristics, river bank geometry, soil properties, grain or flow resistance, channel characteristics and others such as vegetation condition. Relationship between soil erodibility and the riverbank erosion rates is considered as one of the primary processes concerned in the development of channel migration. This research investigates riverbank erosion in the Bernam River, Malaysia. Field monitoring data was collected to obtain sufficient amount of information for variables of riverbank erosion factors i.e. channel geometry, hydraulics characteristics and erodibility in order to explain the controls on temporal changes in riverbank erosion rates.
Field experimental data of soil erodibility measurement were gained using a novel, newly developed Jet Erosion Device (JEd) as shown in Figure 1. The JEd equipment is a fabrication of the previously developed Jet Erosion Test equipment. The purpose of this device is to measure the erodibility parameters of the different type of soils of the riverbanks. The working procedures are similar with some modification to adapt with the field data collection. Soil samples were extracted and tested in the laboratory to obtain the basic soil properties. Bank erosion data using erosion pins and bank profiling methods, channel geometry and hydraulics measurements were also obtained from series of field data collection. Jet Erosion Device (JEd). https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/fig47_1.jpg"/>
Riverbank analysis using the variables obtained through dimensional analysis based on the field data collected were then conducted to identify the relationship of riverbank erosion with the hydraulics, channel and soil characteristics. The dimensionless form of the riverbank erosion relationship as follows: () ε U o = f ( τ o τ c , g d U o 2 , ρ w U o 2 τ c , ρ s U o 2 τ c , H d , S , p , P I ) https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315623207/4fbc492d-6678-4a12-aaf6-5c2b8ea38e5f/content/eq286.tif"/>
where ε is the riverbank erosion, Uo is the depth-averaged velocity for the reach (m/s), τo is the fluid shear stress (N/m2 or kg/ms2), τc is the critical shear stress (N/m2 or kg/ms2), d is the reach-averaged depth (m), g is the gravitational acceleration (m/s2), ρw is the density of water (kg/m3), ρs is the density of sediment particles (kg/m3), H is the bank height (m), S is the averaged longitudinal water-surface slope, P is the bed porosity and PI is the plastic index of the soil.
Statistical analyses using multiple linear and nonlinear regression methods were performed to establish the empirical equation of riverbank erosion based on the selected dependent and independent variables with the incorporation of the soil erodibility parameters. Statistical parameters such as coefficient of determination, R 2, standard error of the estimate and discrepancy ratio percentages were used to aid in the selection of the most appropriate model. The predictive variables selected were based on their ability to explain the variation of riverbank erosion. Once a mathematical model in a form of erosion prediction equation was produced based on the regression of the field data, the results were interpreted and checked against any physical data. This validation process was done with field monitoring data and available secondary data.
