BANK STABILITY ANALYSIS FOR PREDICTING REACH SCALE LAND LOSS AND SEDIMENT YIELD¹

Abstract

When extensive lengths of river become stabilized (e.g., by channel incision), riverbank erosion can result in considerable riparian land loss and the delivery of large volumes of sediment downstream. The ability to predict the stability and failure geometry of eroding riverbanks is therefore an important prerequisite in estimating the rate of bank erosion and sediment yield associated with bank erosion. In this paper, a new stability analysis for layered river banks is introduced. The new analysis differs from many previous analyses in that it takes into consideration the effects of positive pore water pressure in the saturated portion, and negative pore water pressure in the unsaturated portion, of the bank as well as the influence of hydrostatic confining pressure due to the water level in the river. In addition, the failure plane is not constrained to pass through the toe of the bank and the bank profile geometry is not restricted to an idealized special case. The predictive ability of the new bank stability analysis is assessed using data from two field sites. Subsequently, a methodology for applying the bank stability analysis at the scale of the river reach (0.1 to 10 km) is discussed. This method involves the use of empirical models of bed level adjustment to estimate the magnitude of incision at specific locations along the reach, with these estimates used to drive the stability analysis. Application of the new method is demonstrated with an example.

The impact of the streamflow hydrograph on sediment supply from terrace erosion

“…Based on the water table fluctuations modelled above, we modelled erosion of the lateral boundary of our cross-section via infinite slope stability adapted for riverbanks (Amiri-Tokaldany, 2003;Simon et al, 2003), which is applicable only for planar failures that apparently prevail at this site. We extracted a channel-terrace cross section by combining bathymetry with subaerial survey via laser rangefinder to obtain a representative transect of the Rose Bar terrace (Fig.…”

“…The F cp on a riverbank is defined by compressive forces acting upon the bank face (Amiri-Tokaldany et al, 2003) as (8) in which…”

“…However, several other recent research efforts have placed great emphasis on links between boundary water status, bank stability, boundary failure, and in-channel sediment transport (Amiri-Tokaldany et al, 2003, 2007Rinaldi et al, 2004Rinaldi et al, , 2008.…”

Bank‐collapse processes in a valley‐bottom gully, western Iowa

“…Our general goal was to determine through monitoring over a 2-year period whether positive pore pressures associated with subsurface water flow were alone sufficient to instigate bank failures. The role of subsurface water in the failure of gully and river banks has received considerable attention (e.g., Bradford and Piest, 1977;Osman and Thorne, 1988;Higgins et al, 1990;Hagerty, 1991;Darby and Thorne, 1996;Casagli et al, 1999;Simon et al, 2000;Collison, 2001;Simon and Collison, 2001;Amiri-Tokaldany et al, 2003;Dapporto et al, 2001Dapporto et al, , 2003Rinaldi et al, 2004;Darby et al, 2007;Fox et al, 2007;Wilson et al, 2007), and some authors have isolated effects of reduced matric suction in the unsaturated zone (e.g., Fredlund et al, 1978;Casagli et al, 1999;Rinaldi et al, 2004). This study, motivated by observations of bank failures seated below the water table, focuses on only the saturated zone.…”

9 Modelling river-bank-erosion processes and mass failure mechanisms: progress towards fully coupled simulations

“…These include the establishment and evolution of river and floodplain morphology and their associated habitats (e.g., Hooke, 1980;Millar and Quick, 1993;Darby and Thorne, 1996a;Barker et al, 1997;Millar, 2000;Goodson et al, 2002), turbidity problems (e.g., Bull, 1997;Eaton et al, 2004), sediment, nutrient, and contaminant dynamics (e.g., Reneau et al, 2004), loss of riparian lands (e.g., Amiri-Tokaldany et al, 2003), and associated threats to flood defence and transportation infrastructure (e.g., Simon, E-mail address: mrinaldi@dicea.unifi.it (M. Rinaldi) ISSN: 0928-2025DOI: 10.1016/S0928-2025 11126-3 1995). Moreover, recent studies have shown that the contribution of bank-derived sediments to catchment sediment budgets may be higher than previously thought, although the precise fraction varies depending on the time-scale of measurement (Bull, 1997).…”