USGS - Water Resources in Kansas

Sediment Science in Kansas

In Kansas and nationally, sediment is a concern for both physical and chemical reasons. Physically, problems caused by excessive sediment may include degraded water quality, degraded aquatic habitat, increased water-treatment costs, decreased channel capacity, clogged water intakes, and loss of water-storage capacity in reservoirs. Chemically, sediment serves as a carrier for various contaminants and, under certain conditions, as a source of contaminants to water and biota. Sediment-associated contaminants include nutrients (nitrogen, phosphorus), trace elements, certain pesticides, and polychlorinated biphenyls (PCBs). Nationally, sediment has been identified as the most important contaminant of concern by the U.S. Environmental Protection Agency.

Figure 1. Channel-bed degradation in the Big Blue River near Manhattan, Kansas (stream-gaging station 06887000) downstream from Tuttle Creek Dam, as evidenced by change in river stage for the mean annual discharge (2,500 cubic feet per second), 1953-1997.

Sediment Erosion

Several USGS studies have investigated channel erosion in response to human disturbances. To address concerns about possible downstream effects of John Redmond Reservoir on the Neosho River, a study was done to determine whether or not the channel had widened substantially since the reservoir was completed. The post-dam response of the river was determined to be minor with no evidence of substantial widening (Juracek, 2000). In a study to assess the downstream effect of large reservoirs on channel-bed elevation, Juracek (2001) found that degradation lowered channel beds by several feet at some locations (fig. 1). Along Soldier Creek, it was determined that channelization caused substantial channel degradation (widening and deepening). The degradation migrated several miles upstream from the original site of disturbance (Juracek, 2002, 2004a). Additional information on these and other USGS studies is available at http://ks.water.usgs.gov/studies/fluvial/.

Sediment Transport

Effective management of sediment requires information on the amount of sediment being transported at specific locations and how sediment transport varies with time. Currently, the USGS operates a suspended-sediment monitoring network in Kansas that provides several types of useful suspended-sediment information. For example, continuous turbidity and streamflow data are used to provide continuous (hourly) estimates of suspended-sediment concentration and load (fig. 2). The information also is useful for evaluating variability in suspended-sediment load in relation to streamflow during individual runoff events, seasonally, and over the long term. Rasmussen and others (2005) used multi-year data from three continuous water-quality monitoring sites to estimate average annual suspended-sediment (and nutrient) loads and yields for the Kansas River. Suspended-sediment information also can be used to document and explain differences among sites (e.g., because of differences in basin characteristics including precipitation, soils, topography, and land management) as well as provide baseline information to assess the effectiveness of implemented erosion control practices. Information on the USGS suspended-sediment monitoring network for Kansas is available at http://ks.water.usgs.gov/rtqw/.

Table 1. Mean annual sediment yield and mean annual precipitation for selected reservoir basins in Kansas. (source: Juracek, 2004b).

Reservoir basin	Sediment yield (acre-feet per square mile per year)	Mean annual precipitation (inches)
Small reservoir basins
Mound City Lake	2.03	40
Crystal Lake	1.72	40
Mission Lake	1.42	35
Gardner City Lake	.85	39
Otis Creek Reservoir	.71	33
Lake Afton	.66	30
Large reservoir basins
Perry Lake	1.59	37
Hillsdale Lake	.97	41
Tuttle Creek Lake	.40	30
Cheney Reservoir	.22	27
Webster Reservoir	.03	21

In an attempt to explain differences in sediment yield among reservoir basins in Kansas, Juracek (2004b) compared estimated mean annual sediment yields for 11 reservoirs with factors that affect soil erosion. Specifically, the factors included were precipitation, soil permeability, slope, and land use. The analysis indicated that only the relation between mean annual sediment yield and mean annual precipitation was statistically significant (at the 0.05 level of significance). That is, as mean annual precipitation increased, mean annual sediment yield also increased. Thus, for the 11 reservoirs included, mean annual precipitation was the best predictor of sediment yield. Given the pronounced decrease in precipitation from east to west across Kansas, a similar east to west decrease in reservoir sedimentation rates is likely.

Reservoir Sediment Studies in Kansas

The U.S. Geological Survey (USGS), in cooperation with Federal, State, and local agencies, has completed a number of reservoir sediment studies in Kansas (fig. 1) using a combination of bathymetric surveying, sediment coring, chemical analysis, and statistical analysis. Specific objectives of the studies were to: (1) estimate total sediment volume and mass, (2) estimate annual sediment deposition and yield from the basin, (3) determine the occurrence and trends of constituents, (4) estimate annual constituent loads and yields from the basin, (5) assess sediment quality, and (6) provide a baseline for future assessments.

Mill Creek Sediment

Existing and ongoing urban development can cause substantial changes to the streamflow and sediment transport characteristics of area streams. Increased impervious surface cover (rooftops, sidewalks, roads, parking lots) associated with urban development decrease the connection between streams and groundwater, directing precipitation directly into receiving streams. These changes work to increase the flood risk and erode stream channels. New construction activities remove vegetation from surface soils, destabilizing the soil structure, and allowing for increased erosion during precipitation events.

Erosion of surface and stream channel soils increase sediments transported by area streams. These suspended sediments are the cause of many water-quality impairments. Sediments can carry a variety of water-quality contaminants, including nutrients, bacteria, metals, organic matter, and a variety of potentially toxic organic chemicals. Sediments also decrease light penetration to water, and can settle on streambeds, burying habitat for insects and fish.