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COMPUTING TIME-SERIES SUSPENDED-SEDIMENT CONCENTRATIONS AND LOADS FROM IN-STREAM TURBIDITY-SENSOR AND STREAMFLOW DATAby Patrick P Rasmussen and John R. Gray
Guidelines and procedures for estimating time series of suspended-sediment concentration and loading as a function of turbidity and streamflow data have been published in a U.S. Geological Survey Techniques and Methods Report, Book 3, Chapter C4. The concepts, statistical procedures, and techniques used to maintain a multiyear suspended sediment time series and to prepare sediment data for public dissemination are described. Procedures for comparing computed suspended-sediment concentrations to water-quality criteria and assessing the frequency of exceeding criteria are included. Specific examples of the method used in Kansas and Missouri are provided.
The method for computing suspended-sediment concentration and loads using turbidity sensors is primarily for nephelometry, but also can be used for optical backscatter. Because an in-situ turbidity sensor is capable of measuring turbidity instantaneously, a turbidity time series can be recorded and related directly to time-varying suspended-sediment concentrations. Depending on the suspended-sediment characteristics of the measurement site, this method can be more reliable and, in many cases, a more accurate means for computing suspended-sediment concentrations and loads than traditional U.S. Geological Survey computational methods.
A spreadsheet and user manual to develop a single or multiple linear regression model using SSC, turbidity, and streamflow data can be downloaded here (Turbidity Sediment Spreadsheet and User Manual). The macros in this spreadsheet allow the user to paste their data in and interactively develop regression models that can then be used to compute SSC and SSL. The methods discussed in T&M 3C4 are used in the spreadsheet.