Magnitude and distribution of rates of river bank erosion

Abstract

SUMMARYMeasurements of bank erosion on rivers in Devon over a 2f year period produced mean rates ranging from 0.08 to 1.18 metres per year and a maximum rate of 2.58 metres per year. These values are compared with rates derived from maps for various time periods between 1840 and 1975. The map rates are generally lower than the field rates and the question of whether this difference is due to the method of measurement, the magnitude-frequency of events, a change in discharge conditions or the inherent variation in channel activity is discussed. Published data on bank erosion rates are reviewed and the Devon rates are found to coincide with the worldwide distribution. An analysis of factors likely to influence the spatial distribution of erosion rates reveals a square-root relationship to catchment area and the importance of bank material. Implications of the measured rates for development of flood plains are examined. KEY WORDS Erosion Rates Magnitude Distribution Controlling factors MAGNITUDE AND DISTRIBUTION OF RIVER BANK EROSIONA knowledge of rates of errosion is fundamental to full interpretation of the landscape, especially in evaluation of the time period required for development of particular features and in assessment of the influence of climatic, geological and environmental conditions. Thornes and Brunsden (1977) have identified three functions of rates of processes-in testing of models, in provision of parameters and inputs for models, and in practical problems. Data are required for application in these functions but there are severe problems which beset both the measurement of the processes and the extrapolation to the longer term. Many of these problems are associated with sampling both in space and time and are exacerbated by a lack of standardization of terms and methods which makes comparison and accumulation of data difficult. Measurement of river bank erosion has the advantage that the process is relatively rapid compared with many other geomorphological processes but this enhances its importance in interpretation of landscape change. Knowledge of rates of bank erosion is also of value in investigation of the effects of human activities on channel processes and in short-term prediction of erosion and planning of erosion control. METHODS OF MEASUREMENT

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

“…A fine bed material (noncohesive) is easier to transport and erode. As Nanson and Hickin (1986) showed, the bed material size at the Hooke (1980) M~A (drainage area) M~% silt-clay in bank Hickin and Nanson (1975), Nanson and Hickin (1983) M~R c /W Also identified bank texture, planform, and sediment supply rate as important Begin (1981) M~R c /W Nanson and Hickin (1983) M~Q and S M~W and S M~Q, S and D 50 M~W, S and D 50 Hickin and Nanson (1984) M~R c /W Also identified bank resistance as important Biedenharn et al (1989) M~R c /W toe of the slope can be a good indication of the resistance of the bank. At the other extreme, for instance downstream from a dam, armored beds are no longer mobile and the flow often scours the banks.…”

“…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).…”

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

“…Fluvial erosion is defined as the removal of bank material by the action of hydraulic forces, although it generally occurs in combination with weathering processes that prepare bank sediments for erosion by enhancing their erodibility (Hooke, 1980;Thorne, 1982;Lawler, 1993; ASCE Task Committee on Hydraulics, Bank Mechanics, and Modeling of River Width Adjustment, 1998;Prosser et al, 2000;Couper and Maddock, 2001). Relative to mass failure, fluvial erosion is, at the scale of the flow event and once the critical entrainment threshold has been exceeded, a quasi-continuous process, with the volume of sediment delivered by fluvial erosion dependent on the duration of the competent flow.…”

“…However, this simple conceptualisation masks enormous complexity that results from the inherent variability of the relevant controlling parameters. Thus, observed rates of fluvial-erosion range over several orders of magnitude (Hooke, 1980) and fluvial-erosion rates are predictable only to the extent that the controlling parameter values, and their inherent variability, can be estimated accurately. It is widely accepted that the rate of fluvial bank erosion can be quantified using an excess shear stress formula such as (Partheniades, 1965;Arulanandan et al, 1980):…”

“…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).…”