Trends in Suspended-Sediment Concentration at Selected Stream Sites in Kansas, 1970–2002

Knowledge of erosion, transport, and deposition of sediment relative to streams and impoundments is important to those involved directly or indirectly in the development and management of water resources. Monitoring the quantity of sediment in streams and impoundments is important because:

(1) sediment may degrade the water quality of streams for such uses as municipal water supply,

(2) sediment is detrimental to the health of some species of aquatic animals and plants, and

(3) accumulation of sediment in water-supply impoundments decreases the amount of storage and, therefore, water available for users.

Time-trend tests for 13 of 14 sediment sampling sites in Kansas for the period from about 1970 to 2002 indicated that 3 of the 13 sites tested had statistically significant decreasing suspended-sediment concentrations; however, only 2 sites, Walnut River at Winfield and Elk River at Elk Falls, had trends that were statistically significant at the 0.05 probability level. Increasing suspended-sediment concentrations were indicated at three sites although none were statistically significant at the 0.05 probability level. Samples from five of the six sampling sites located upstream from reservoirs indicated decreasing suspended-sediment concentrations. Watershed impoundments located in the respective river basins may contribute to the decreasing suspended-sediment trends exhibited at most of the sampling sites because the impoundments are designed to trap sediment. Both sites that exhibited statistically significant decreasing suspended-sediment concentrations have a large number of watershed impoundments located in their respective drainage basins. The relation between percentage of the watershed affected by impoundments and trend in suspended-sediment concentration for 11 sites indicated that, as the number of impoundments in the watershed increases, suspended-sediment concentration decreases. Other conser-vation practices, such as terracing of farm fields and contour farming, also may contribute to the reduced suspended-sediment concentrations if their use has increased during the period of analysis.

Regression models were developed for 13 of 14 sediment sampling sites in Kansas and can be used to estimate suspended-sediment concentration if the range in stream discharge for which they were developed is not exceeded and if time trends in suspended-sediment concentrations are not significant. For those sites that had a statistically significant trend in suspended-sediment concentration, a second regression model was developed using samples collected during 2000–02. Past and current studies by the U.S. Geological Survey have shown that regression models can be developed between in-stream measurements of turbidity and laboratory-analyzed sediment samples. Regression models were developed for the relations between discharge and suspended-sediment concentration and turbidity and suspended-sediment concentration for 10 sediment sampling sites using samples collected during 2000–02.

CONTENTS

Abstract
Introduction
Background
Factors Affecting Sediment Transport
Study Methods

Site Selection and Sample Collection Development of Regression Models and Trend Analysis
Results of Trend Analysis
Evaluation of Trend Results
Use of Turbidity to Develop Regression Equations for Estimating Suspended-Sediment Concentration
Future Sediment Data-Collection Needs
Summary and Conclusions
References
Supplemental Information

Putnam, J.E., and Pope, L.M., 2003, Trends in suspended-sediment concentration at selected stream sites in Kansas, 1970–2002: U.S. Geological Survey Water-Resources Investigations Report 03–4150, 36 p.

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