Filtration of Sediment by Simulated Vegetation II. Unsteady Flow with Non-Homogeneous Sediment

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Abstract
REDUCTION of sediment yield from disturbed areas such as strip mines and construction sites has continued to be a problem. Vegetal filtration has previously been recommended as a means of reducing the quantity of sediment which reaches the streams and rivers (USEPA, 1976). However, the lack of exact design cri-teria has caused this method to be more an artistic than a scientific procedure. Barfield et al. (1975, 1978) and Kao et al. (1975) have summarized the previously available information on the process of sediment trapping and flow hydraulics. Recent successful studies (Barfield et al., 1978) using uniformly sized particles in simulated erect vegetation have led to a series of equations which have been proposed to define the deposition within a grass filter. These equations utilized a spacing hydraulic radius to define the characteristic length applicable to the calcula-tion of a Reynold's number. Prediction of mean velocity and channel bottom drag force were determined using this Reynold's number. These relationships were than used in conjunction with Einstein's sediment transport parameters for determination of total load transport in an artificial media. Barfield et al. (1979) presented a model for making these predictions for steady flow con-ditions. These equations have now been extended to a continuity model for the prediction of the sediment pro-file with non-uniform particle sizes and time-varying in-flows. In addition, some example calculations are shown in this report which demonstrate the sensitivity of the model to changes in various parameters under unsteady flow conditions.

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