Showing papers on "Bank erosion published in 2001"

Large-scale patterns of erosion and sediment transport in river networks, with examples from Australia

Abstract: This paper examines the patterns of sediment transport in rivers in terms of the sources of sediment and its transport and deposition through the river network. The analysis is in the context of dramatic human influences on river sediment transport and how they might influence freshwater ecosystems. The review of Australian work shows that erosion of hillslopes and stream banks has greatly increased in historical times, supplying vast quantities of sediment to rivers, much of which is still stored within the river system. The stored sediment will continue to effect in-stream and estuarine ecosystems for many decades. In most Australian catchments the dominant source of sediment is streambank erosion. An analysis of historical channel widening suggests that a conceptual framework of relative stream power can explain the diversity of behaviour observed in the numerous case studies. Sediment delivery through catchments is considered first in a generic whole network sense, which emphasizes the crucial role played by riverine deposition in determining catchment sediment budgets. A method is then presented for analysing the diverse spatial patterns of sediment storage in any river network. Finally, the paper considers the temporal changes to channel morphology in response to a human-induced pulse of sediment.

Patterns of Instream Wood Recruitment and Transport at the Watershed Scale

Abstract: A wood budget was constructed for the Game Creek basin (132 km2) in southeast Alaska to identify spatial and temporal controls on the abundance and distribution of large woody debris (LWD). Field measurements of wood storage, size, and age were used to estimate volumetric rates of LWD recruitment and transport. Mortality recruitment did not follow a spatial pattern and ranged from 0.1 to 8.1 m3·km−1·year−1 (recruitment corresponded to forest mortality rates of 0.1–2.6% per year). Wood recruitment by bank erosion increased with increasing drainage area and ranged from 1 m3·km−1·year−1 at the smallest drainage areas to about 16 m3·km−1·year−1 at 60 km2. Bank erosion recruitment exceeded the maximum mortality recruitment at a drainage area of approximately 20 km2 (about 10-m-wide channel). Recruitment from land-sliding was only locally significant. The contribution of fluvial transport (flux) to total LWD storage increased with drainage area to an asymptotic maximum of 50% at about 50 km2 (about 20-...

Subaerial river bank erosion processes and their interaction with other bank erosion mechanisms on the River Arrow, Warwickshire, UK

Abstract: River bank erosion occurs primarily through a combination of three mechanisms: mass failure, fluvial entrainment, and subaerial weakening and weathering. Subaerial processes are often viewed as ‘preparatory’ processes, weakening the bank face prior to fluvial erosion. Within a river basin downstream process ‘domains’ occur, with subaerial processes dominating the upper reaches, fluvial erosion the middle, and mass failure the lower reaches of a river. The aim of this paper is to demonstrate that (a) subaerial processes may be underestimated as an erosive agent, and (b) process dominance has a temporal, as well as spatial, aspect. Bank erosion on the River Arrow, Warwickshire, UK, was monitored for 16 months (December 1996 to March 1998) using erosion pins. Variations in the rate and aerial extent of erosion are considered with reference to meteorological data. Throughout the first 15 months all erosion recorded was subaerial, resulting in up to 181 mm a−1 of bank retreat, compared with 13 to 27 mm a−1 reported by previous researchers. While the role of subaerial processes as ‘preparatory’ is not contended, it is suggested that such processes can also be erosive. The three bank erosion mechanisms operate at different levels of magnitude and frequency, and the River Arrow data demonstrate this. Thus the concept of process dominance has a temporal, as well as spatial aspect, particularly over the short time-periods often used for studying processes in the field. Perception of the relative efficacy of each erosive mechanism will therefore be influenced by the temporal scale at which the bank is considered. With the advent of global climate change, both these magnitude–frequency characteristics and the consequent interaction of bank erosion mechanisms may alter. It is therefore likely that recognition of this temporal aspect of process dominance will become increasingly important to studies of bank erosion processes. Copyright © 2001 John Wiley & Sons, Ltd.

Erosion and sediment delivery following removal of forest roads

Abstract: Erosion control treatments were applied to abandoned logging roads in California, with the goal of reducing road-related sediment input to streams and restoring natural hydrologic patterns on the landscape. Treatment of stream crossings involved excavating culverts and associated road fill and reshaping streambanks. A variety of techniques were applied to road benches, which included decompacting the road surface, placing unstable road fill in more stable locations, and reestablishing natural surface drainage patterns. Following treatment and a 12-year recurrence-interval storm, some road reaches and excavated stream crossings showed evidence of mass movement failures, gullying, bank erosion and channel incision. Post-treatment erosion from excavated stream crossings was related to two variables: a surrogate for stream power (drainage area channel gradient) and the volume of fill excavated from the channel. Post-treatment erosion on road reaches was related to four explanatory variables: method of treatment, hillslope position (upper, mid-slope or lower), date of treatment, and an interaction term (hillslope position method of treatment). Sediment delivery from treated roads in upper, middle and lower hillslope positions was 10, 135 and 550 m 3 of sediment per kilometre of treated roads, respectively. In contrast, inventories of almost 500 km of forest roads in adjacent catchments indicate that untreated roads produced 1500 to 4700 m 3 of sediment per kilometre of road length. Erosion from 300 km of treated roads contributed less than 2 per cent of the total sediment load of Redwood Creek during the period 1978 to 1998. Although road removal treatments do not completely eliminate erosion associated with forest roads, they do substantially reduce sediment yields from abandoned logging roads. Published in 2001 by John Wiley & Sons, Ltd.

Use of Vanes for Control of Scour at Vertical Wall Abutments

Abstract: Rock vanes are single-arm structures angled to the flow with a pitch into the streambed such that the tip of the vane is submerged even during low flow. Vanes have primarily been used in recent years for treatment of bank erosion in stream stability projects. These structures roll the water away from the eroding banks, thus limiting erosion of the channel banks. They have proven to be very effective treatments over a range of flow conditions. In this project, the effectiveness of vanes for preventing scour at single-span bridges with vertical wall abutments was evaluated based on laboratory experiments. The vanes were tested in small-scale experiments in a recirculating flume and subjected to a range of flow conditions, including bank full and a number of overbank flows, which were forced to return to the channel at the abutment. The results showed that the vanes were highly effective in moving the scour away from the abutment into the center of the channel under all flow conditions tested. Based on the experimental results, optimum design settings for the vane angle and height, most effective number of vanes, and distance upstream for placement of the first vane were determined.

Geomorphic control of persistent mine impacts in a Yellowstone Park stream and implications for the recovery of fluvial systems

Abstract: A half-century after mine closure, metal contamination from sulfide ore mining in the headwaters continues to impair riparian vegetation and aquatic macroinvertebrates along Soda Butte Creek, Yellowstone National Park. A tailings dam failure in 1950 emplaced metal-rich sediment at high flood-plain levels, above 50 yr to 100 yr flood stages in 1996 and 1997. These large natural floods removed only a small part of the contaminated sediment through bank erosion; they also failed to lower in-channel Cu concentrations, because increased erosion of mine waste during high flows balances increased inputs of uncontaminated sediments, generating no net change in concentrations. Geomorphic processes controlling movement of contaminated sediments indicate that mine impacts will persist for centuries in Soda Butte Creek and imply long-lasting impacts in similarly affected streams worldwide.

Application of a Novel Automatic Erosion and Deposition Monitoring System at a Channel Bank Site on the Tidal River Trent, U.K.

Abstract: There is a well-defined need to improve understanding of the dynamics of sediment erosion and deposition on intertidal channel banks, given their importance to channel stability, sediment budgets, depth maintenance, pollutant and nutrient transport, and ecological processes in estuarine systems. Conventional, manual methods for field monitoring of erosion and deposition, however, normally deliver information of low temporal resolution conditioned by infrequent field resurveys. To address this problem, this paper discusses a recently developed and improved automatic erosion and deposition monitoring technique, the Photo-Electronic Erosion Pin (PEEP) system, and its application to a tidal channel bank site at Burringham on the River Trent, U.K. The PEEP system allows the magnitude, frequency and timing of individual erosion and deposition events to be monitored much more precisely than with conventional manual methods. PEEP sensors also monitor light intensity and sediment temperature, variables which can influence bank stabilizing and destabilizing processes. Example results at both the event and spring-neap timescales are presented from a short PEEP system deployment between March and May 1997 at Burringham. These establish that discrete erosion events of >60 mm and 100 mm can occur in response to individual tidal cycles, events which are readily monitored automatically and quasicontinuously by the PEEP system. The capability of the PEEP approach to enhance temporal resolution of monitoring is demonstrated by the determination of the timing of the 100-mm bank erosion incident to an ‘ event window ’ of 2·75 h: this converts to mean bank erosion rate of 36 mm h−1over the period of inundation. In addition, the PEEP system defines the magnitude and date of two example deposition events of 47 and 92 mm on the lower bank during a sequence of rising spring tides. These represent mean deposition rates of 4·5 and 8·4 mm h−1respectively over the periods of inundation. The Burringham site is shown to be highly active, with regular and dynamic erosion and deposition cycles. Upper bank surface elevation oscillations, driven by this sediment cycling, were characterized by a strong 14-day cycle which clearly reflected the spring-neap cycling of tidal range. Sediment was deposited on the bank relatively quickly, but removed by erosion rather slowly, giving an asymmetric sediment cycling profile. Higher bank elevations were strongly correlated with high tidal ranges, and especially to water level peaks 2 days previously. Incorporation of a simple Wind Stress Index further improved the statistical explanation of tidal bank elevation, and suggested that high on-shore wind speeds were associated with increased bank erosion. Such vigorous sediment cycling means that many erosion-deposition sequences on tidal banks can be self-concealing and therefore may not be recorded by infrequent manual resurveys which will inevitably underestimate total activity. This reinforces the need for an automated method such as the PEEP system to determine these typically cyclic sequences of self-cancelling accretion and removal activity if site dynamism is to be correctly quantified. The ability of the PEEP approach to generate such detailed and high-resolution information on the temporal distribution of erosion and deposition events in tidal environments should significantly enhance future process and applied studies, especially of entrainment thresholds, sediment recycling, estuarine sediment supply and sediment fluxes, the operation of biomediation mechanisms, bank erodibility changes, storage and residence times of contaminants and site management options.

Movable bed scour around submerged spur-dikes

Abstract: This paper presents the results of an exploratory study on scour occurring around submerged spur-dike. The effect of flow depth and spur-dike dimensions was studied with the help of the experimental data. It was found that the overtopping ratio and the opening ratio are significantly affected on the maximum scour depth. The larger opening ratios (α) caused relatively small scour area and the bank erosion downstream the spur-dike hardly can occur. The longer spur-dike length & the lower flow depth produced scour area wider than the shorter spur-dike length & the higher flow depth. The data collected in this investigation would be useful for the development of numerical models of scour around submerged dikes.

Topographic factors for RUSLE in the continuous-simulation watershed model for predicting agricultural, non-point source pollutants (AnnAGNPS).

Abstract: RUSLE (Revised Universal Soil Loss Equation) is the basis within AnnAGNPS (Annualized AGricultural Non-Point Source Pollution watershed model) for estimating sheet and rill erosion (clay, silt, sand, small and large aggregates) of a watershed’s landscape. This sheet and rill erosion is used to predict fine sediment yield (clay and silt) from the watershed landscape by AnnAGNPS, which is a continuous-simulation, agricultural-related, non-point source, pollutant loading, watershed model. The fine sediment yield from sheet and rill erosion of agricultural lands generally is a major concern for pollutant loadings within water bodies. Other sources of sediment (gullies and bed and bank erosion) are also predicted by AnnAGNPS, but only RUSLE is used to estimate the sheet and rill erosion. The basic parameters used in RUSLE are the: (1) rainfall factor (R); (2) soil erodibility factor (K); (3) topographic factor (LS); (4) cover-management factor (C); and (5) support practice factor (P). The LS-factor is time invariant and can be determined directly from digital elevation models (DEMs). The purpose of AnnAGNPS is to predict expected pollutant loading for each storm event-not a conservative estimate along a critical profile in the field. Therefore, it is important to determine the LS-factor for each homogenous land area within the watershed (a cell in AnnAGNPS) to reproduce the expected erosion for a homogenous land area if the other RUSLE parameters are known. The topographic factor routine for AnnAGNPS follows each DEM raster along its respective flow path and recognizes where and when sheet and rill can occur. By using the slope length and steepness factor algorithms for irregular and segmented slopes (Renard et al., 1997), a raster-weighted LS-factor for each homogenous land area can be determined. The accuracy of the resulting LS-factors are a function of the horizontal and, in particular, the vertical raster resolution of the DEM.

Desktop method for estimating vessel-induced sediment suspension

Abstract: Riverbank erosion involves engineering and environmental concerns. Among several dominant mechanisms of riverbank erosion, navigation effects caused by the passage of vessels are quite important. Field data indicate that large vessels generate large drawdown and small wave heights, whereas small vessels such as pleasure craft generate small drawdown and large wave heights. Passage of both types of vessels may result in bank erosion and a substantial increase in suspended-sediment concentration. Since comprehensive numerical modeling is time-consuming, a desktop computational approach has been offered that helps in providing preliminary answers to several questions related to vessel-induced sediment resuspension. Due to the uncertainties inherent in sediment calculations, order-of-magnitude values are often adequate for decision making. A preliminary assessment of possible impact on vegetation or benthic organisms can then be made based on this information. PC-based FORTRAN programs were developed for (1) computation of time series of vessel-induced waves; (2) erosion and deposition of cohesive sediment under waves and nearshore currents; and (3) computation of noncohesive suspended-sediment concentration caused by river current alone. An application to the Upper Mississippi River Navigation Study is presented. The riverbank sediments were labeled as soft, medium, and hard using their erodibility characteristics. Three water depths (0.5, 1.0, and 1.5 m) were considered. Vessel-induced wave heights ranged from 10 to 60 cm. The maximum concentrations were obtained in 0.5 m water depth with a wave height of 30 cm and in 1.0 m depth with a wave height of 60 cm. The estimated maximum concentrations were 1,463, 56, and 4 mg/L for soft, medium, and hard beds, respectively. Such results will be useful for preliminary assessment of relative impact of increased barge traffic in the river and identification of potential areas along the riverbanks that are likely to be sensitive from the point of view of environmental considerations.

Regime theory and the stability of straight channels with bankfull and overbank flow

Abstract: Experiments have been carried out at a large laboratory scale to test a rational regime theory and to study the development of regime channel morphology for straight loose-boundary channels (bed and banks) in fixed flood plains for a range of flow conditions. Results are presented for straight channels which have been developed with bankfull flows and then subjected to overbank flows, and include friction and sediment transport data. These indicate reasonable theoretical agreement with the friction data but the sediment transport rate is underestimated. Stability of the main channel was assessed in response to bedforms, bank erosion and hydraulic friction and sediment transport. For overbank flows, rates of bank erosion have been measured. These measurements constitute unique overbank widening data for the main channel.

Topographic expressions of bars in channels with variable width

Abstract: A three dimensional quasi-analytical model is introduced to determine the flow field and the altimetric response of movable-bed channels subject to periodic width variations. The basic assumptions underlying the analysis are those of small amplitude of width variations and wide channel, so that non linear effects and side wall effects are neglected. The aim of the work is to determine the conditions under which the channel is planimetrically stable or unstable, i.e. it tends to damp (or enhance) a given initial (infinitesimal) perturbation of the channel width due to bank erosion. A simple bank erosion model is adopted whereby the rate of bank retreat is related to the excess shear stress at the banks. Theoretical results suggest that the equilibrium bottom profile is mainly constituted by two components. The first component represents a purely longitudinal bottom deformation, which induces deposition at the widest section and scour at the constraint, where the cross sectionally averaged velocity attains its maximum value. The second component is mainly originated by three dimensional effects and induces a transverse deformation of the bed in the form of a central bar. Its relative position with respect to the former component changes with the length of width variations: under suitable conditions the flow divergence induced by the central bar leads to a maximum velocity at the banks in wide sections, which implies that width variations tend to amplify.

Simulation of Streambank Erosion Processes with a Two-Dimensional Numerical Model

Abstract: Channel stabilization is critical for the success of channel restoration. A stable channel, from a geomorphic perspective, is one that has adjusted its width, depth, and slope such that there is no significant aggradation or degradation of the streambed or significant platform changes within an engineering time frame, generally less than 50 years (Biedenharn et al., 1997). Even though the bed of a stream in dynamic equilibrium is neither degrading nor aggrading, erosion may be occurring in stream banks and result in bank instability. Bank protection is often required even for a stream in dynamic equilibrium. Due to the lack of understanding of bank erosion mechanisms, the hydraulic and sediment transport models, including the series of U.S. Army Corps of Engineers Hydrologic Engineering Center models, CH3D-SED, etc., which have been widely applied to engineering projects to design stable channels, can only predict the vertical bed adjustments due to degradation and aggradation. Alluvial channels adjust themselves to reach regime conditions not only through bed elevation changes but also through platform evolution, for example, the migration of meandering channels.

Effects of simulated water level management on shore erosion rates. Case study: Baskatong Reservoir, Québec, Canada

Abstract: This study was carried out as part of a feasibility study on the construction of a hydroelectric generating station at Mercier dam at the outlet of the Baskatong reservoir in Quebec. The study dealt mainly with a comparison of the current and future bank erosion rates of the reservoir. Given the year of impounding of the Baskatong reservoir, i.e., 1927, it was possible to track bank erosion rates using field surveys and photogrammetric and numerical analyses. It was noted that in certain areas, such as Du Diable Bay and Windigo Bay, the Baskatong reservoir banks were substantially affected by erosion. Estimates indicate that the banks have receded by about 10 to 15 m over a 20-year period. The banks most affected by erosion are those containing sandy material of fluvioglacial or glaciolacustrine origin with bluffs greater than 2 m in height and characterized by the longest fetches. In one section of Windigo Bay, banks had receded by about 30 m in 20 years. Wave action is the main factor responsible for ba...

Subaerial River Bank Processes and Interaction with other Bank Erosion Mechanisms on the River Arrow, Warwickshire, UK

Abstract: River bank erosion occurs primarily through a combination of three mechanisms: mass failure, fluvial entrainment, and subaerial weakening and weathering. Subaerial processes are often viewed as preparatory processes, weakening the bank face prior to fluvial erosion. Within a river basin downstream process domains occur, with subaerial processes dominating the upper reaches, fluvial erosion the middle, and mass failure the lower reaches of a river. The aim of this paper is to demonstrate that (a) subaerial processes may be underestimated as an erosive agent, and (b) process dominance has a temporal, as well as spatial, aspect. Bank erosion on the River Arrow, Warwickshire, UK, was monitored for 16 months (December 1996 to March 1998) using erosion pins. Variations in the rate and aerial extent of erosion are considered with reference to meteorological data. Throughout the first 15 months all erosion recorded was subaerial, resulting in up to 181 mm a-1 of bank retreat, compared with 13 to 27 mm a-1 reported by previous researchers. While the role of subaerial processes as preparatory is not contended, it is suggested that such processes can also be erosive. The three bank erosion mechanisms operate at different levels of magnitude and frequency, and the River Arrow data demonstrate this. Thus the concept of process dominance has a temporal, as well as spatial aspect, particularly over the short time-periods often used for studying processes in the field. Perception of the relative efficacy of each erosive mechanism will therefore be influenced by the temporal scale at which the bank is considered. With the advent of global climate change, both these magnitude-frequency characteristics and the consequent interaction of bank erosion mechanisms may alter. It is therefore likely that recognition of this temporal aspect of process dominance will become increasingly important to studies of bank erosion processes.

River Geometry, Bank Erosion, and Sand Bars within the Main Stem of the Kankakee River in Illinois and Indiana

Abstract: This is the third and final report on the Kankakee River in Illinois supported by the Conservation 2000 Program of the Illinois Department of Natural Resources. For this project, the Illinois State Water Survey mapped the bank erosion of the main stem of the Kankakee River from the Route 30 bridge in Indiana to the mouth of the Kankakee River with the Illinois River near Wilmington, collected about 100 bed and bank material samples, resurveyed all the previously surveyed river cross sections, surveyed four sand bars, and analyzed all historical and new data. This research has shown that of 223.6 river bank miles (includes both sides of the river), about 10.4 river bank miles have severe erosion, 39.4 river bank miles have moderate erosion, 70.8 river bank miles have minor erosion, and the remainder are either protected or stabilized or data are not available. The median diameter of the bed materials varied from 0.27 millimeters (mm) to 0.52 mm. The median diameter of bank materials varied from 0.07 mm to 0.41 mm. Analyses of the long-term flows from six gaging stations in Illinois showed an increasing trend in flows through the 1960s with no discernible increase since that time. Cross-sectional analyses of the river from the Kankakee Dam to the State Line Bridge did show some trends. The river reach from the Kankakee Dam to Aroma Park called SixMile Pool has lost 13.4 percent of its capacity due to sediment deposition since 1980. Similarly, Momence Wetland also has lost about 10.2 percent of its capacity since 1980. The section of the river between Aroma Park and Singleton Ditch showed both scour and sediment deposition. In general areas close to Aroma Park exhibited sediment deposition and the middle reach experienced scour. The recurring sand bar at the State Line Bridge area contains about 8,500 cubic yards of additional sediment in 1999 than were measured in 1980. The volumetric measurement of three additional sand bars showed some changes since 1980. The river is accumulating sediments within Six-Mile Pool and Momence Wetland. The middle reach is in semi-equilibrium with some sediment accumulation at several areas. Several management alternatives, both in-channel and watershed-based also are included to assist in the reduction of sedimentation problems of the Kankakee River.

Quantifying River Bank Erosion with Scanning Laser Altimetry

Abstract: Detailed topographic data collected with an airborne laser scanner can help determine the extent of bank erosion and identify banks that are more vulnerable to bank collapse and thus require stabilization efforts. The Minnesota River which flows through a 95% agricultural watershed has been ranked among the top 20 most polluted rivers in the U.S. Greater than 50% of the sediment load carried by the river at Mankato, MN is delivered by a single tributary, the Blue Earth River. A 56km length of the main stem of the Blue Earth River corridor was scanned April 2001 with an helicopter mounted Topeye laser system. The database includes X, Y, Z coordinates of laser returns from the river valley plus return intensity. Other data collection included ground elevation measurements for two banks using a total station, and vegetation density at eight locations along the river. A bare earth model was constructed by removing returns from vegetation and is currently being tested against the ground elevation measurements. Plans are to make another scan in a year or more to calculate volumetric change in the river valley due to bank erosion / bank collapse. This volume change along with soil bulk density along the river corridor will be used to assess the extent of bank erosion. The mass wasting rates will then be converted to total suspended sediments assuming fine silt and clay fractions are most likely to be transported.

Noosa Riverbank Erosion Investigation Stage 1: Analysis of Bank Erosion

Abstract: An investigation was undertaken to identify the possible causes of bank erosion along a 10 kilometre section of the Noosa River. Anecdotal evidence suggests that up to 5 metres of the riverbank has been lost over the past 10 years in the river reach located between the shallow lakes of Cootharaba and Cooroibah. Evidence of recent erosion throughout the reach included fallen trees and slumping and undercutting of the riverbank. Possible causes of bank erosion investigated include changes to the catchment hydrology, natural meander processes, hydrodynamic changes in the river, changes to the bank soil condition and wave action caused by boats. These causes were examined by hydraulic modelling of the reach for flood and tide flows, analysis of recorded tide data, assessment of the geomorphology and direct measurement of the reach cross-section profile, bank alignment, channel and near bank velocity and boat wake height. The investigation identified that boat wash is the dominant cause of bank erosion in the study reach. Bank soil characteristics and patterns of land usage at certain sections of the reach resulted in differing rates and severity of erosion.

Results From a Channel Restoration Project: Hydraulic Design Considerations

Abstract: Techniques for the hydraulic restoration of placer-mined streams and floodplains were developed in Denali National Park and Preserve, Alaska. The two-year study at Glen Creek focused on a design of stream and floodplain geometry using hydraulic capacity and shear stress equations. Slope and sinuosity values were based on regional relationships. Design requirements included a channel capacity for a bankfull discharge and a floodplain capacity for a 1.5- to 100-year discharge. Several bio-engineering techniques using alder and willow, including anchored brush bars, streambank hedge layering, seedlings, and cuttings, were tested to dissipate floodwater energy and encourage sediment deposition until natural revegetation stabilized the new floodplains. Permanently monumented cross-sections installed throughout the project site were surveyed every one to three years. Nine years after the project began, a summer flood caused substantial damage to the channel form, including a change in width/depth ratio, slope, and thalweg location. Many of the alder brush bars were heavily damaged or destroyed, resulting in significant bank erosion. This paper reviews the original hydraulic design process, and describes changes to the channel and floodplain geometry over time, based on nine years of cross-section

Large-scale patterns of erosion and sediment transport in river networks, with examples from Australia (vol 52, pg 91, 2001)

Abstract: This paper examines the patterns of sediment transport in rivers in terms of the sources of sediment and its transport and deposition through the river network. The analysis is in the context of dramatic human influences on river sediment transport and how they might influence freshwater ecosystems. The review of Australian work shows that erosion of hillslopes and stream banks has greatly increased in historical times, supplying vast quantities of sediment to rivers, much of which is still stored within the river system. The stored sediment will continue to effect in-stream and estuarine ecosystems for many decades. In most Australian catchments the dominant source of sediment is streambank erosion. An analysis of historical channel widening suggests that a conceptual framework of relative stream power can explain the diversity of behaviour observed in the numerous case studies. Sediment delivery through catchments is considered first in a generic whole network sense, which emphasizes the crucial role played by riverine deposition in determining catchment sediment budgets. A method is then presented for analysing the diverse spatial patterns of sediment storage in any river network. Finally, the paper considers the temporal changes to channel morphology in response to a human-induced pulse of sediment.

Analysis of vegetation controls on bank erosion rates, Clark Fork of the Columbia River, Deer Lodge Valley, Montana

Abstract: The Clark Fork of the Columbia River through Deer Lodge Valley, Montana, is a meandering stream that has experienced high cutbank erosion rates over the past several decades due to extreme thinning of woody riparian vegetation. Bank erosion rate data available for the period 1989 to 1997 were examined along with large-scale aerial photographs in order to assess the relation between vegetation along cutbanks in meander bends and cutbank erosion rates. These data clearly show a downward trend in erosion rate with increasing density of woody riparian vegetation. Where vegetation density is high and erosion rates are low, however, the amount of bank retreat cannot be determined from the aerial photographs. Consequently, a lower limit on erosion rate as a function of density of woody riparian vegetation cannot be calculated from the available data.

Coastal Inlet Bank Erosion

Abstract: : Much focus is placed on beach erosion on the open coast However, coastal processes often occur on sandy shorelines interior to inlets that can lead to severe erosion These shorelines lie adjacent to coastal inlets and extend around the inlet from the ocean to bay In particular, an examination of coastal inlets with jetties or terminal groins that are connected to a sandy shoreline develop inner-bank erosion in the absence of preventive measures Many mature projects show eroded regions that required extensive revetment Typically, if the erosion is permitted to proceed unabated, a crenulate-shaped shoreline region will develop from the terminus of the jetty, extending both bayward and laterally into the adjacent beach This expansion of erosion leads to loss of property and difficulties in reclamation as a shallow water environment develops The eroded sediment moves into the channel creating shoaling problems Many times the eroded region may flank the jetty structure, leaving it isolated from the shore Isolation of the jetty may lead to potential problems of tidal current scour near the structure, opening the already eroded embayment to increased wave activity and additional erosion, and permitting increased wave attack on the jetty itself As part of the Coastal Inlets Research Program (US Army Corps of Engineers), this type of erosion was studied in a movable bed physical model of an inlet After the governing processes were understood, several preventive techniques were investigated A case study is included