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Optimal Estimation of Suspended-Sediment Concentrations in Streams

Hydrologic Processes by John Wiley, Hydrologic Processes v.15
Lansing, Michigan 2001

By David J. Holtschlag


Optimal estimators are developed for computation of suspended-sediment concentrations in streams. The estimators are a function of parameters, computed by use of generalized least-squares, that simultaneously account for affects of streamflow, seasonal variations in average sediment concentrations, a dynamic error component, and the uncertainty in concentration measurements. The parameters are used in a Kalman filter for on-line estimation and an associated smoother for off-line estimation of suspended-sediment concentrations. The accuracies of the optimal estimators are compared with alternative interpolation and regression estimators by use of long-term daily-mean suspended-sediment concentration and streamflow data from 10 sites within the United States. For sampling intervals from 3 to 48 days, the standard errors of on-line and off-line optimal estimators ranged from 52.7 to 107 percent, and from 39.5 to 93.0 percent, respectively. The corresponding standard errors of linear and cubic-spline interpolators ranged from 48.8 to 158 percent, and from 50.6 to 176 percent, respectively. The standard errors of simple and multiple regression estimators, which did not vary with the sampling interval, were 124 percent and 105 percent, respectively. Thus, the off-line estimator (Kalman smoother) had the lowest error characteristics among the estimators evaluated. Because suspended-sediment concentrations are typically measured at less than three-day intervals, use of optimal estimators will likely result in significant improvements in the accuracy of continuous suspended-sediment concentration records. Additional research on the integration of direct suspended-sediment concentration measurements and optimal estimators applied at hourly or shorter intervals is needed.

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David J. Holtschlag, U.S. Geological Survey, 6520 Mercantile Way, Suite 5, Lansing, Michigan 48911,


National Stream Quality Accounting Network (NASQAN)

Holtschlag, D.J., 2001, Optimal Estimation of Suspended-Sediment Concentrations in Streams: Hydrologic Processes by John Wiley, Hydrologic Processes v.15, p. 1133-1155.

Holtschlag, D.J., 2001, Computation of suspended-sediment concentrations in streams--Proceedings of the Seventh Federal Interagency Sedimentation Conference, March 25-29, 2001, Reno, Nevada, v. 2, pp. VI-17 to VI-24.

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