Data from an optical turbidity sensor deployed at the stream station were recorded at 15-minute intervals by a data logger and uploaded every hour to the U.S. Geological Survey (USGS) database (Anderson, 2005; Wagner, 2006). Suspended-sediment samples were collected using a suction pump autosampler, equal width increments or grab sampling techniques (Edwards, 1999). The use of an optical sensor to continuously monitor turbidity provided an accurate estimate of sediment fluctuations without the collection and analysis costs associated with intensive sampling (Office of Surface Water memorandum 2016.07; Rasmussen et al., 2009). Turbidity was used as a surrogate for suspended-sediment concentration (SSC), which is a measure of sedimentation and siltation. Regression models were developed between SSC and turbidity using turbidity data from the optical sensor and the SSC data collected from the suspended-sediment samples.
For Osage Creek near Cave Springs, AR, a total of 56 suspended-sediment samples were collected beginning on March 20, 2012 and ranged from 1 to 1480 milligrams per liter across a range of turbidity from 0.8 to 911 formazin nephelometric units and streamflow from 26.6 to 5640 cubic feet per second. There were 40 suspended-sediment samples used in the final model after removing samples associated with sampling or fouling errors and extraneous samples from the same storm event which would result in overfitting of the model.
