Showing papers on "Stream power published in 2001"

Sediment and rock strength controls on river incision into bedrock

Abstract: Recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply, challenging the common assumption that incision rate is simply proportional to stream power. Our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by providing tools for abrasion, but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits. Maximum erosion rates occur at a critical level of coarse-grained sediment supply where the bedrock is only partially exposed. Fine-grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension. Experiments also reveal that rock resistance to fluvial erosion scales with the square of rock tensile strength. Our results suggest that spatial and temporal variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate. Furthermore, we conclude that the grain size distribution of sediment supplied by hillslopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief.

Quantifying differential rock-uplift rates via stream profile analysis

Abstract: Despite intensive research into the coupling between tectonics and surface processes, our ability to obtain quantitative information on the rates of tectonic processes from topography remains limited due primarily to a dearth of data with which to test and calibrate process rate laws. Here we develop a simple theory for the impact of spatially variable rock-uplift rate on the concavity of bedrock river profiles. Application of the analysis to the Siwalik Hills of central Nepal demonstrates that systematic differences in the concavity of channels in this region match the predictions of a stream power incision model and depend on the position and direction of the channel relative to gradients in the vertical component of deformation rate across an active fault-bend fold. Furthermore, calibration of model parameters from channel profiles argued to be in steady state with the current climatic and tectonic regime indicates that (1) the ratio of exponents on channel drainage area and slope ( m / n ) is ∼0.46, consistent with theoretical predictions; (2) the slope exponent is consistent with incision either linearly proportional to shear stress or unit stream power ( n = 0.66 or n = 1, respectively); and (3) the coefficient of erosion is within the range of previously published estimates (mean K = 4.3 × 10 −4 m 0.2 /yr). Application of these model parameters to other channels in the Siwalik Hills yields estimates of spatially variable erosion rates that mimic expected variations in rock-uplift rate across a fault-bend fold. Thus, the sensitivity of channel gradient to rock- uplift rate in this landscape allows us to derive quantitative estimates of spatial variations in erosion rate directly from topographic data.

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.

Effects of urbanization on channel instability

Abstract: Channel instability and aquatic ecosystem degradation have been linked to watershed imperviousness in humid regions of the U.S. In an effort to provide a more process-based linkage between observed thresholds of aquatic ecosystem degradation and urbanization, standard single event approaches (U.S. Geological Survey Flood Regression Equations and rational) and continuous hydrologic models (HSPF and CASC2D) were used to examine potential changes in flow regime associated with varying levels of watershed imperviousness. The predicted changes in flow parameters were then interpreted in concert with risk-based models of channel form and instability. Although low levels of imperviousness (10 to 20 percent) clearly have the potential to destabilize streams, changes in discharge, and thus stream power, associated with increased impervious area are highly variable and dependent upon watershed-specific conditions. In addition to the storage characteristics of the pre-development watershed, the magnitude of change is sensitive to the connectivity and conveyance of impervious areas as well as the specific characteristics of the receiving channels. Different stream types are likely to exhibit varying degrees and types of instability, depending on entrenchment, relative erodibility of bed and banks, riparian condition, mode of sediment transport (bedload versus suspended load), and proximity to geomorphic thresholds. Nonetheless, simple risk-based analyses of the potential impacts of land use change on aquatic ecosystems have the potential to redirect and improve the effectiveness of watershed management strategies by facilitating the identification of channels that may be most sensitive to changes in stream power.

The Cross-Vane, W-Weir and J-Hook Vane Structures…Their Description, Design and Application for Stream Stabilization and River Restoration

Abstract: The descriptions, design specifications, placement locations, spacing and various applications of Cross-Vane, W-Weir and J-Hook Vane structures are presented. These structures were developed and subsequently applied to: 1) establish grade control, 2) reduce streambank erosion, 3) facilitate sediment transport, 4) provide for irrigation diversion structures, 5) enhance fish habitat, 6) maintain width/depth ratio, 7) improve recreational boating, 8) maintain river stability, 9) dissipate excess energy, 10) withstand large floods, 11) maintain channel capacity, 12) be compatible with natural channel design, and 13) be visually acceptable to the public. Relations to determine the minimum size of rock for these structures are presented based on bankfull shear stress. Drawings for each structure are provided that display appropriate use of footers, cross-section shape, profile shape, appropriate channel locations, angles, slopes, spacing and elevations. Velocity isovels are presented to describe changes in the distribution of energy produced by the structures. The structures all reduce near-bank shear stress and stream power, while increasing center channel shear stress and stream power to retain both flood-flow and sediment transport capacity. These structures have been installed on 14 rivers with bankfull widths varying from 9m (Lower Blanco River in Southwestern Colorado) to 150m (Bitterroot River in Northwestern Montana) and slopes varying from 0.05 to .0003 and in bed material ranging from cobble and gravel to sand bed streams. Since 1986, the author has restored and monitored a wide variety of stream types involving over 48 km of rivers and evaluated various structure performance following major floods. This monitoring has resulted in the development, implementation and assessment of the Cross-Vane, W-Weir and J-Hook vane structures.

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.

Transport of sediment in large sand-bed rivers

Abstract: A sediment transport equation based on universal stream power is presented for the prediction of bed-material concentrations in large sand-bed rivers. The universal stream power, which is derived from the energy concept, has the advantage of eliminating the energy slope as a parameter. The energy slope, which is in the order of 10-5 for large rivers, is a major source of uncertainty in measurements. The analysis shows that relationships derived from flume experiments with shallow flows cannot be universally applied to large rivers with deep flows. Also the use of dimensionless homogeneous parameters in an equation is not sufficient to ensure its applicability to flow conditions where flow depths are several orders of magnitude larger. The comparisons between computed and measured sediment concentrations indicate that the commonly used Engelund and Hansen, Ackers and White, and Yang equations which were developed using mainly flume experiments are not applicable for large rivers with flow depths and Reynol...

A geomorphologist's criticism of the engineering approach to channelization of gravel-bed rivers: case study of the Raba River, Polish Carpathians.

Abstract: River engineers use sediment transport formulas to design regulated channels in which the river's ability to transport bedload would remain in equilibrium with the delivery of materials from upstream In gravel-bed rivers, a number of factors distort the simple relationship between particle size and hydraulic parameters at the threshold of sediment motion, inherent in the formulas This may lead to significant errors in predicting the bedload transport rates in such streams and hence to instability of their regulated channels The failure to recognize a nonstationary river regime may also result in unsuccessful channelization Rapid channel incision has followed channelization of the main rivers of the Polish Carpathians in the 20th century A case study of the Raba River shows that incision has resulted from the increase in stream power caused by channelization and the simultaneous reduction in sediment supply due to variations in basin management and a change in flood hydrographs Calculations of bedload transport in the river by the Meyer-Peter and Muller formula are shown to have resulted in unrealistic estimates, perhaps because the different degree of bed armoring in particular cross-sections was neglected It would have been possible to avoid improper channelization if the decreasing trend in sediment load of the Carpathian rivers had been recognized on the basis of geomorphological and sedimentological studies Allowing the rivers to increase their sinuosity, wherever possible without an erosional threat to property and infrastructure, and preventing further in-stream gravel mining are postulated in order to arrest channel incision and reestablish the conditions for water and sediment storage on the floodplains

Empirical predictors of annual bed load travel distance, and implications for salmonid habitat restoration and protection

Abstract: Measurements of annual travel distance (Lb) of bed load sediment at 16 locations in Alaska, the intermountain USA, west coast USA and Scotland are strongly correlated with bankfull channel width (r2 = 0·86, p < 0·001). Travel distance of particles is probably limited by trapping in bars, which have a longitudinal spacing proportional to channel width. Increased abundance of woody debris reduces bar spacing and may reduce Lb. Longer cumulative duration of bed load transporting flows in a year appears to increase Lb. Other predictors of annual travel distance such as stream power per unit length, drainage area and bankfull discharge were less well correlated with Lb (r2 ranging from 0·27 to 0·51). Stream power per unit bed area, basal shear stress and slope were not significantly related to Lb (r2 < 0·05). Most correlations were improved when regressions were limited to data from the west coast USA. Travel distance estimates can be used to help identify reaches that may take longer to recover from large, short-term increases in sediment supply. Published in 2001 by John Wiley & Sons, Ltd.

Applicability of sediment transport formulas

Abstract: The paper provides a comprehensive testing of the applicability of 13 sediment transport formulas under different flow and sediment conditions. The dimensionless parameters used for testing the reliability and sensitivity of formulas are dimensionless particle diameter, relative depth, Froude number, relative shear velocity, dimensionless unit stream power, and sediment concentration. A total of 3,391 sets of laboratory and river data are used in the tests. Engineers may find the test results useful to their selection of formulas under different flow and sediment conditions.

Regional-scale sedimentation process models from airborne gamma ray remote sensing and digital elevation data

Abstract: Airborne gamma ray survey data were used to provide information on potassium, thorium and uranium concentrations in surface soil and rock in arid central Australia. Spatial patterns in these radioelements allow tracing of paths of sediment at catchment scale. Survey elevation data are combined with contour data to produce digital elevation models for terrain analysis, tracing of sediment flow paths and modelling of extreme floods. Gamma ray data show consistent variation with slope, a limited range of drainage areas, and erosion/deposition models derived from the conservation of mass equation. Supply-limited sediment transport models give a reasonable reproduction of observed radioelement distribution but some elements of the distribution pattern reflect the area inundated by 500–1000 year floods rather than the effects of simple downslope movement. Partial area sediment supply models are derived by downstream accumulation of erosion and deposition rates calculated using the conservation of mass equation with transport laws based on slope alone and stream power. Comparison with observed radioelement patterns suggests that both transport laws apply in different parts of the landscape. Regional-scale sediment transport models will require a range of models depending on location in the landscape and event frequency. This approach may allow estimation of sediment delivery ratios. Copyright © 2001 John Wiley & Sons, Ltd.

Corrigendum to: 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.

Influence of sediment transport on armored surfaces

Abstract: Laboratory experiments have been carried out to study the characteristics of sediment transport in steep streams. The question is discussed wether an armoured surfaces is destroyed due to the transport of material, because additional impulses are acting on it, or the layer is sheltered by the transported material, because a part of the stream power is used to move the material. According to the results of the presented experiments, in which the influence of the feeding rate and the feeding duration have been investigated, transported material reaching an armoured river section from upstream always remobilzes bed material, which is immobile under clear water flow conditions. To decide if a static armour layer is either destroyed or not, two simple criteria were chosen: oneconsidering the grain-size distribution of the eroded bed material, and another, which referes to the amount of eroded bed material.

Observed Thresholds of Stream Ecosystem Degradation in Urbanizing Areas: A Process-Based Geomorphic View

Abstract: Recent studies suggest that channel instability and aquatic ecosystem degradation occur at low levels of watershed imperviousness in humid regions of the U.S. In an effort to provide a more process-based explanation of observed thresholds of aquatic ecosystem degradation in urbanizing areas, U.S. Geological Survey (USGS) gauging data and simple hydrologic techniques were used to examine likely increases in discharge associated with varying levels of watershed imperviousness. The probable increases in these flow parameters for an annual flooding event were compared with analyses of a data set describing 270 stable and unstable channels from diverse geographic regions. Results suggest that a 10 - 20% increase in watershed imperviousness can result in a level of specific stream power that exceeds that corresponding to a high risk of instability for streams poised near a geomorphic threshold. Although risk of channel instability may be associated with different levels of watershed imperviousness, factors such as specific stream power relative to sediment caliber and channel entrenchment provide a more direct assessment of channel sensitivity to urbanization. Linking potential increases in specific stream power with the risk of channel instability establishes a more process-based connection between imperviousness and observed thresholds of aquatic ecosystem degradation.

Interbasin Consistency of Hydraulic Geometry and Its Relationships with Basin Morphology and Hydrology

Abstract: The width, mean depth, and mean velocity of a stream are typically power functions of discharge, whose exponents are unit-sum constrained. The appropriate methodology for testing statistical hypotheses involving such data is compositional data analysis (CDA). Prior to the advent of CDA, the Illinois State Water Survey (ISWS) undertook statewide and national studies of hydraulic geometry in which they developed an index called proportional stream order, which uses rational numbers to quantify the variation within a stream segment of a given order. The current investigation applies CDA to that data and to other hydrologic and morphologic parameters that are potential covariates of hydraulic geometry. Logratio linear modeling demonstrated that at-a-station hydraulic geometry was unrelated to proportional stream order in the Sangamon basin in central Illinois. The downstream hydraulic geometry of twelve basins in the humid region of the U.S. had atypicality indices consistent with a single, logistic ...

Modeling Package for Assessing the Potential Effects of Hydrologic Change on Stream Form and Integrity

Abstract: Existing models can be used to assess the potential hydrologic effects of land-use change, but practical tools for translating these results into predictions regarding channel stability and effects on stream biota are currently unavailable to local planners. To improve watershed management in the context of changing land uses, we are developing a flexible, changeable package of small mechanistic models, statistical models, and expert scientific judgment to provide estimates of long-term changes in stream erosion potential, channel morphology, and instream disturbance regime. We are focusing primarily on the development of a Visual Basic / Excel package of stream / land-use management modules that are designed to operate with either continuous or single-event hydrologic input. Based on input channel geometry and flow series, the various modules provide users with estimates of the following characteristics for pre- and post-land use change conditions: (1) the temporal distribution of shear stress, specific stream power, and potential mobility of various particle sizes; (2) potential changes in channel cross sections as a result of altered flow and sedimentation regimes; (3) frequency, depth, and duration of scour; (4) effective discharge / sediment yield; (5) sediment transport capacity based on selected transport equations; and (6) analytical computation of stable channel dimensions. An attractive feature of this approach for stormwater management is a set of user-friendly tools to examine timeintegrated sediment transport and scour characteristics across a range of flows and time periods associated with varying stormwater mitigation schemes. Ultimately, these modules will give end users a suite of tools to compare the erosive potential of hydrographs, to depict channel changes that might result from different land-use management scenarios, and to improve interpretation of biomonitoring information through consistent quantification of stream disturbance regimes.

Parameter Identifiability for Three Sediment Entrainment Equations

Abstract: A process-based erosion model is used to study parameterization problems of sediment entrainment equations in overland flow areas. One of the equations for entrainment by flow is developed based on a theory of excess stream power, while the other two relate to excess hydraulic shear. The investigation is conducted in two steps. The first step examines parameter optimization for simulated data sets where the parameter values are known. In the second step, parameter optimization for the most robust equation is examined using experimental data from rainfall simulator plots. Results demonstrate that although the model is capable of estimating total sediment yields with relatively small errors in parameter estimates, the converse is true when the optimization is performed for sediment concentrations. Although sediment yields calculated from simulated sediment concentrations match well with observed data, the parameter estimates generally underestimate sediment concentrations on the rising limb of the sediment graphs, and they overestimate them on the falling limb. This difficulty might be related to structural problems in the model, and unique solutions for parameter estimates cannot be obtained.

Bedload transport in a meltwater stream, Miers Valley, Antarctica: controls and prediction

Abstract: Bedload transport rates in a meltwater stream in the Miers Valley of Antarctica are highly variable. The major control on the transport of the predominantly sand-sized material is the energy available as a function of discharge; however, the relationship is neither simple nor constant. Change in discharge was able to explain 85% of the variation in bedload transport rates at a site where intensive sampling was undertaken over two 12-hour periods. At discharges below approximately 2401 s -1 bedload transport rates vary as a simple power function of discharge. At greater discharges the relationship becomes less regular. The bedform changes from ripples to sand waves and dunes and, as these migrate past the sampling site, they cause wide fluctuations in bedload flux. The higher velocities also exceed the erosion threshold of the sands that make up the banks, leading to undercutting and bank collapse if the ice cementing the sands thaws. This results in random pulses of sediment which cause further variation in the actual transport rates. Bagnold's equation, although it predicted the general trend in bedload transport, does not work well in an absolute sense, even in this relatively simple study reach. It under-estimates bedload transport rates by a factor of five. However, once corrected for depth and grain size a transport equation based on excess stream power could explain 90% of the variation in the measured bedload transport rate. The slope of this relationship is consistent with that previously reported.

Morphodynamics of the Mississippi River

Abstract: : The Lower Mississippi River, extending from Cairo, Illinois to the Gulf of Mexico, annually transports approximately 170 million tonnes of sediment. Historically, the quantity and calibre of sediment derived from catchment erosion have been affected by changes in land-use and management. For example, soil erosion increased during the 19th and early 20th centuries due to settlement by Europeans and this may have elevated catchment sediment supply to the Mississippi River, while more recently the supply of sediment from tributaries is known to have decreased markedly as a result of river engineering and management. Specifically, the construction of large dams as part of the Mississippi River and Tributaries (MRT Dardeau and Causey, 1990). However, a case can be made that the bed material load must have increased since the 1940s. This argument is based on analysis of morphological changes observed along the river that have led to an overall increase in slope and available stream power, coupled with the fact that bed material sizes along the river have remained almost constant.

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.

A rainfall-sediment-runoff model in the upper Brantas River, East Java, Indonesia

Abstract: A distributed rainfall-sediment-runoff model is constructed to investigate flood and sediment movement on a catchment scale. The model treats spatial data sets such as topography and land cover effectively by applying GIS (geoglaphical information system) and remote sensing techniques. This research uses GIS to produce a DEM (digital elevation model) and remotely sensed data to classify land cover. The model constructed here is a grid-cell-based distributed model. The grid-cell-based kinematic wave model calculates rainfall-runoff and sediment is yielded when overland flow occurs on each grid-cell with surface volcanic soil layer. A primitive model (Takara, 2000) assumed that sediment was yielded with infiltration depth D regardless of energy of overland flow, which has limitation to transport sediment on each grid-cell. Considering a transportation capacity of overland flow on each grid-cell makes it possible to model both sediment yield processes and sediment deposit processes. The unit stream power theory decides the transportation capacity. Yielded sediment in slope grid-cells moves in the flow direction derived from the DEM to river grid-cells, on which bed load and suspended load are calculated. The model is applied to the Lesti River basin (625 km 2 ) located in the upper Brantas River basin, and simulates sediment runoff during a rainy season from November 1995 to April 1996.

Numerical Simulation of Sediment Yield, Storage, and Channel Bed Adjustments

Abstract: The response of alluvial channels to perturbations in the balance of water and sediment inflow is one of the fundamental issues facing geomorphologists and hydraulic engineers. As far back as the first half of the 20th century Ruby (1933) and Makin (1948) were developing concepts and quantitative expressions for the adjustments that occurred when a stream channel at grade was subjected to an change in the steady-state balance of the water and sediment loads it received. In the 1970s fluvial geomorphologists began focusing on the importance of thresholds in determining whether a particular reach of a stream channel would have a tendency to erode, aggrade, or remain stable over the short run (e.g., Schumm, 1973; Bull, 1979). In order to facilitate inferences to be made without recourse to excessive amounts of data and/or overly involved calculations, fairly simple conceptual models invoking channel slope, water discharge, sediment discharge, and derivatives of those basic variables such as boundary layer shear stress, and stream power were used to explain many aspects of how channels adjust to variations in water flow and the character of sediments in the channel.

Flood Frequency Characteristics for Selected Kentucky Streams

Abstract: A study of peak discharges for 54 stream gauge sites in the Cumberland, Tennessee and Mississippi watersheds of Kentucky is presented. Primary interest is on the more frequent flood events, those events associated with return periods less than 5 years. The magnitude and variability of the recorded flood events is described, as well as the frequency model fitted to the observed peak flow record. The importance of the higher frequency events is presented in the context of channel forming flow, bankfull discharge, effective discharge, and mean annual discharge (FISRWG 1998). These results are relevant as a consideration in stream restoration where the more frequent flood events have an important role in restoration project design and channel stability. This aspect will be investigated using the concepts proposed by Costa and O’Connor (1995) where the components of flow duration, stream power per unit area, flood energy, and other characteristics were used to represent the effectiveness of floods as sources of geomorphic changes to channels and floodplains.