Watershed Assessment

Cheney Reservoir and Watershed Study

The U.S. Geological Survey began cooperative studies of the Cheney Reservoir watershed with the city of Wichita in 1996. Initial studies determined the chemical loading into and out of Cheney Reservoir, changes in reservoir sediment quality over time, and chemical loading from various sub-basins within the watershed. Phosphorus and sediment were identified as the major contaminants in Cheney Reservoir, although salinity, metals, selenium and pathogen indicator bacterial (fecal coliform) also were of concern. In addition, reservoir sediment studies documented an increasing trend in phosphorus concentrations over time. More recent studies (2000-2006) have focused on real-time estimation of water-quality constituent concentrations and transport from the watershed and the description of in-reservoir conditions that may result in the production of algal blooms and taste-and-odor compounds. Models using variables measured by real-time water-quality monitors successfully were developed to provide hourly estimates of the concentrations nutrient, sediment, and taste-and-odor compounds. Ongoing studies at Cheney Reservoir will refine the relations between reservoir and inflow conditions and taste-and-odor occurrences. The city of Wichita plans to use these models, along with other variables measured in real time, to aid in the management of the resource and decrease water-treatment costs.

Water-Quality Assessment of Streams in Johnson County, Kansas

Johnson County, located in northeast Kansas, is the most populated county in the State according to the 2000 U.S. census, with more than 450,000 people. Urban, industrial, and agricultural land uses affect the water quality of streams and lakes in the county. Water-quality impairments have been identified by the Kansas Department of Health and Environment in several Johnson County streams including the Blue River and Indian, Mill, Cedar and Kill Creeks. Stream impairments are caused primarily by sediment, nutrients, and bacteria.

This study is providing comprehensive assessment of water-quality conditions in streams throughout Johnson County. Results will assist the county and its cities in identifying contaminant source areas and in developing and evaluating land-management plans that affect water quality.

Mill Creek Sediment Sources

The Mill Creek watershed drains 62.8 square miles within the cities of Olathe, Lenexa, and Shawnee (Figures 1, 2). The watershed has undergone residential and commercial development primarily in the east (Lenexa and Shawnee) and south (Olathe) and is among the most rapidly developing areas in Johnson County, KS. New construction is occurring in many of the undeveloped portions of the basin.

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.

Specifically, the study is estimating concentrations and loads of suspended sediment at 8 sites within the Mill Creek watershed and estimating sources of suspended sediment using chemical tracer techniques and stormflow sediment dynamics.