| Abstract: | The time-dependent response of sediment suspension to flow velocity was explored by modeling field measurements collected in the surf zone during a large storm. Linear and nonlinear models were created and tested using flow velocity as input and suspended-sediment concentration as output. A sequence of past velocities (velocity history), as well as velocity from the same instant as the suspended-sediment concentration, was used as input; this velocity history length was allowed to vary. The models also allowed for a lag between input (instantaneous velocity or end of velocity sequence) and output (suspended-sediment concentration). Predictions of concentration from instantaneous velocity or instantaneous velocity raised to a power (up to 8) using linear models were poor (correlation coefficients between predicted and observed concentrations were less than 0.10). Allowing a lag between velocity and concentration improved linear models (correlation coefficient of 0.30), with optimum lag time increasing with elevation above the seabed (from 1.5 s at 13 cm to 8.5 s at 60 cm). These lags are largely due to the time for an observed flow event to effect the bed and mix sediment upward. Using a velocity history further improved linear models (correlation coefficient of 0.43). The best linear model used 12.5 s of velocity history (approximately one wave period) to predict concentration. Nonlinear models gave better predictions than linear models, and, as with linear models, nonlinear models using a velocity history performed better than models using only instantaneous velocity as input. Including a lag time between the velocity and concentration also improved the predictions. The best model (correlation coefficient of 0.58) used 3 s (approximately a quarter wave period) of the cross-shore velocity squared, starting at 4.5 s before the observed concentration, to predict concentration. Using a velocity history increases the performance of the models by specifying a more complete description of the dynamical forcing of the flow (including accelerations and wave phase and shape) responsible for sediment suspension. Incorporating such a velocity history and a lag time into the formulation of the forcing for time-dependent models for sediment suspension in the surf zone will greatly increase our ability to predict suspended-sediment transport. |
| Genre: | Article |
| ProdID: | 70018689 |
| Citation Author: | Jaffe, B. E.; Rubin, D. M. |
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| Citation End Page: | 14296 |
| Citation Issue: | C6 |
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| Citation Language: | English |
| Citation Larger Work Title: | Journal of Geophysical Research C: Oceans |
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| Citation Number Of Pages: | 14 |
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| Citation Search Results Text: | Using nonlinear forecasting to learn the magnitude and phasing of time-varying sediment suspension in the surf zone; 1996; Article; Journal; Journal of Geophysical Research C: Oceans; Jaffe, B. E.; Rubin, D. M. |
| Citation Start Page: | 14283 |
| Citation Volume: | 101 |
| Citation Year: | 1996 |
| Type: | citation/reference |
| Text: | Using nonlinear forecasting to learn the magnitude and phasing of time-varying sediment suspension in the surf zone; 1996; Article; Journal; Journal of Geophysical Research C: Oceans; Jaffe, B. E.; Rubin, D. M. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Mon, 1 Jan 1996 00:00 -0600 |
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