Downstream change in river bank erosion rates in the Swale-Ouse system, northern England

Abstract

Abstract:Few studies have considered downstream changes in bank erosion rates and variability along single river systems. This paper reports some preliminary results of an intensive and direct ®eld monitoring exercise of bank erosion rates on 11 sites along 130 km of the 3315 km 2 Swale-Ouse river system in northern England over a 14 . 5 month period. Data were collected at active sites using grid networks of erosion pins read at c. 18±30 day intervals and bank-line resurveys. Erosion rates were relatively high for a river of this scale: spatially averaged bank erosion magnitudes over the 14 . 5 months varied from 82 . 7 mm to 440 . 1 mm, although at one highly mobile reach retreat of 1760 mm was recorded over 4 months. Bank erosion rates tended to peak in mid-basin, possibly because of an optimum combination there of high stream powers and erodible bank materials, as predicted theoretically by Lawler (1992Lawler ( , 1995. The piedmont (upland±lowland transition) zone was especially active. Graphical erosion representations for speci®c periods, however, showed that bank retreat was often highly localized within individual sites. Strong seasonal variations in erosion rate were also observed with a signi®cant winter (December±March) peak. A novel ®nding, however, was the apparent downstream increase in the length of the erosion`season', with measurable retreat occurring at the lower sites from September to July. This is interpreted as a re¯ection of a richer mix of bank erosion processes at the downstream sites, where mass failure,¯uid entrainment and weathering processes are all active, with each process group having its own, but overlapping, temporal (seasonal) domain.

Statistical analysis of lateral migration of the Rio Grande, New Mexico

“…Hooke (1979), Nanson and Hickin (1986), MacDonald (1991), and Lawler et al (1999) found that lateral migration rates increase with flow energy in meandering rivers. Bledsoe and Watson (2001) found that measures of stream power were significantly correlated with the degree of lateral stability in river channels measured by the transition to braiding.…”

“…Habitat restoration efforts often require a laterally mobile channel whereas engineering management often attempts to reduce risk to riverside structures and communities through a laterally stable channel. Lateral migration rates can vary both spatially and temporally within a single river reach (e.g., Hooke, 1980;Lawler et al, 1999). Anthropogenic impacts such as dam construction can affect migration rates as well (e.g., Xu, 1996Xu, , 1997Shields et al, 2000).…”

Flow Hydrodynamics across Open Channel Flows with Riparian Zones: Implications for Riverbank Stability

“…Subaerial erosion involves changes in soil moisture, which effectively weakens the streambank leading to the collapse of slabs of soil [15,17]. Hydraulic erosion, including sediment transport due to turbulent flows, may be more pronounced following subaerial erosion [16].…”

Which offers more scope to suppress river phytoplankton blooms: Reducing nutrient pollution or riparian shading?

“…Given the apparent sensitivity of phytoplankton growth to shading, the relatively higher concentrations in the Swale of light-attenuating suspended sediments (SS) ( Table 1) may offer an explanation. The predominant source of the elevated levels in the Swale has been attributed to bank erosion (Lawler et al, 1999). Furthermore, the middle reaches of the Swale are more densely shaded by trees than those in the Ure.…”