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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]

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]

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.

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.

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]

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.