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Erosion of rock masses by water typically involves unraveling of blocks of rock along existing defects in a manner that is not represented by analytical solutions for sediment transport or rockfill (rip-rap). A pragmatic approach to this complex problem is found by using a rock mass index to represent the erodibility of the rock-mass. The likelihood of erosion is then assessed by comparison against case studies in similar rock masses. A new independent data set of rock-mass erosion was gained from inspection of 26 unlined spillways in Australia, South Africa, and the United States. It was found that erosion can be usefully correlated against various published rock mass indices and hydraulic indices. A modified rock mass index, developed specifically to represent erodibility, is presented, and is applied to prepare a new comparative erosion assessment method for rock masses. [ABSTRACT FROM AUTHOR]

This work aims to shed some light on longshore sediment transport (LST) in the highly energetic northwest coast of Portugal. Data achieved through a sand-tracer experiment are compared with data obtained from the original and the new re-evaluated longshore sediment transport formulas (US ACE Waterways Experiment Station's Coastal Engineering and Research Center, Kamphuis, and Bayram bulk formulas) to assess their performance. The field experiment with dyed sand was held at Ofir Beach during one tidal cycle under medium wave-energy conditions. Local hydrodynamic conditions and beach topography were recorded. The tracer was driven southward in response to the local swell and wind- and wave-induced currents (Hsb = 0.75 m, Tp = 11:5 s, θb = 8 - 12°). The LST was estimated by using a linear sediment trans-port flux approach. The obtained value (2.3 x 10-3 m³ ⋅ s-1) approached the estimation provided by the original Bayram formula (2.5 x 10-3 m³ ⋅ s-1). The other formulas overestimated the transport, but the estimations resulting from the new re-evaluated formulas also yield approximate results. Therefore, the results of this work indicated that the Bayram formula may give satisfactory results for predicting the longshore sediment transport on Ofir Beach. [ABSTRACT FROM AUTHOR]

In the mid-Atlantic region of the United States, sediment loads from stream runoff generally change more rapidly in the rising limb than in the falling limb of a storm hydrograph. As a result, sediment load reaches its peak prior to flow peak, an observation known as clockwise hysteresis. This dynamic load–flow relationship is poorly reproduced by the existing multivariate linear regression models. This paper explores regressors that attempt to incorporate observed features in a statistical model and thus improve load estimates. These included inverse discharge and flow-change regressors. The load estimates using three regression models for eight rivers are compared, and recommended regression equations are proposed. [ABSTRACT FROM AUTHOR]

Previous studies assessing the accuracy of bed-load transport equations have considered equation performance statistically based on paired observations of measured and predicted bed-load transport rates. However, transport measurements were typically taken during low flows, biasing the assessment of equation performance toward low discharges, and because equation performance can vary with discharge, it is unclear whether previous assessments of performance apply to higher, geomorphically significant flows (e.g., the bankfull or effective discharges). Nor is it clear whether these equations can predict the effective discharge, which depends on the accuracy of the bed-load transport equation across a range of flows. Prediction of the effective discharge is particularly important in stream restoration projects, as it is frequently used as an index value for scaling channel dimensions and for designing dynamically stable channels. In this study, we consider the geomorphic performance of five bed-load transport equations at 22 gravel-bed rivers in mountain basins of the western United States. Performance is assessed in terms of the accuracy with which the equations are able to predict the effective discharge and its bed-load transport rate. We find that the median error in predicting effective discharge is near zero for all equations, indicating that effective discharge predictions may not be particularly sensitive to one’s choice of bed-load transport equation. However, the standard deviation of the prediction error differs between equations (ranging from 10% to 60%), as does their ability to predict the transport rate at the effective discharge (median errors of less than 1 to almost 2.5 orders of magnitude). A framework is presented for standardizing the transport equations to explain observed differences in performance and to explore sensitivity of effective discharge predictions. [ABSTRACT FROM AUTHOR]

We present a computational approach for identifying the significance of uncertainty in assessing the consequences of sediment and nutrient transport in a section of the Chattahoochee River south of Lake Lanier, as it passes through Atlanta, Georgia. Specifically, our analysis aims at identifying the key control and management actions, and the key scientific uncertainties about the fluvial system, that govern the attainment of a set of water quality objectives for the downstream boundary of the study area. To this end, we present a computational framework that integrates a recently developed sediment-nutrient dynamics model with a Monte Carlo-based methodology for model uncertainty evaluation. Our results suggest that, in general, reliable execution of controls and management actions is more crucial to meeting the target values for flow, sediment, and phosphorus concentration, than the scientific uncertainties associated with fluvial processes within the river channel. We also discuss the potential utility of our framework for accommodating the various science- and policy-derived uncertainties in the total maximum daily load process. [ABSTRACT FROM AUTHOR]

Presents a model study that evaluated sediment transport in a geomorphic channel proposed for restoration and flood damage reduction of an 11-kilometer tidally influenced reach of the Napa River located in California. Objective of the model study; Description on the hydrodynamic and sediment transport models; Model calibration; Conclusions.

Presents a study which examined the effects of vegetative practices on suspended sediment discharge from ponderosa pine forests and pinon-juniper woodlands in Arizona. Details on the study area; Procedures; Conclusions.

Presents information on a study which measured the total longshore sediment transport rate in the surf zone by impoundment at a temporary groin installed at Indian Rocks Beach in Florida. Methods for field measurements of the longshore transport rate and their technical difficulties; Study area and methodology; Results; Conclusions.

Focuses on a study on the sediment erodibility in Boston Harbor, Massachusetts. Reasons for the selection of flume on the assessment of sediment erosion; Opinion on the measurement of erodibility during steady and unsteady flow conditions; Methodology of the study; Results and discussion of the study; Conclusions.

Examines the effects of wave-enhanced bottom friction on storm-driven circulation in Massachusetts Bay, Massachusetts. Wave and circulation fields; Average weigh heights; Relationship between sediment resuspension and surface wave intensity; Bottom drag coefficient enhancement due to waves.

This paper describes a systematic methodology for predicting the fate and stability of dredged material disposal sites over long periods of time, ranging from months to years. The approach is based on the generation and use of databases of wave and current time series that describe environmental conditions specific to the site. These boundary conditions are used to drive a coupled hydrodynamic, sediment transport, and a bathymetry change model that provides a prediction of the long-term behavior of a disposal site of arbitrary dimensions. An example of an application of this approach is made for a moderately dispersive disposal mound located offshore of the entrance to Mobile Bay, Ala. [ABSTRACT FROM AUTHOR]

Field data from Perdido Key, Florida, describing the response of an evolving beach nourishment project and the causative forces are analyzed in terms of sediment-transport rates and gradients. Numerical models for planform and profile evolution are applied and tested against the field data. Commonly applied concepts within the coastal engineering community regarding the “depth of closure,” profile “equilibration,” and the best-choice coefficient for use in a predictive equation for longshore sediment transport rate are discussed. The results indicate that the beach planform may be described qualitatively by an analytical solution, and a one-line numerical model gives a reasonable quantitative description of the longshore gradient of longshore sediment transport. The depth to which longshore sediment transport gradients affect the profile appears to be much less than the depth to which profile changes are observed, illustrating the importance of cross-shore sediment transport. An existing profile-response model, slightly modified, yielded good results immediately following nourishment, but poorer results as the beach profile approached a more natural configuration. [ABSTRACT FROM AUTHOR]

Evaluates a series of box models to determine the extent to which streamflow separation was capable of reproducing the observed variability in metal transport for the Aberjona River near Boston, Massachusetts. Inclusion in the model of subunits for sub-basins draining directly toward the Aberjona River; Sub-basin draining a major tributary; Ground-water withdrawal.

Evaluates processes controlling streamflow generation and suspended sediment transport for the Aberjona River watershed in Boston, Massachusetts. Storage effects of large reservoirs; Suspended sediment response for tributary; Pattern of nonvolatile concentration.

A 30-year simulation of fine-grained, cohesive sediment transport in Watts Bar Reservoir, located in Tennessee, demonstrated that the SEDZL model realistically predicts overall patterns of erosion and deposition throughout this large reservoir. Good qualitative agreement was achieved between the predicted and observed trends in the net sediment-bed-elevation change during the model-calibration period, from 1961 to 1991. Quantitative comparison of predicted and measured bed elevation changes indicated that the model was generally able to accurately simulate local erosion and deposition within Watts Bar Reservoir, yielding a median absolute relative error of 46% in the cohesive sediment bed areas of the reservoir. The model predicted that 76% of the incoming sediments during this 30-year period would be trapped in the reservoir, which is in excellent agreement with the observed trapping efficiency of 72 ±6% (95% confidence interval). [ABSTRACT FROM AUTHOR]

Discusses correlations of calculated time-integrated excess skin friction stress and sediment sand content in Quincy Bay in outer Boston Harbor, Massachusetts. Correlation of the excess shear stress with sediment lead; Site description; Existence of low contaminant concentrations in some low shear stress sites.