Johnson County
Stormwater Management
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This project is conducted
in cooperation with the
Johnson County
Stormwater Management Program.
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Sources of suspended sediment in the
Mill Creek watershed, Johnson County, KS
Increased
suspended sediment transport associated with storm runoff at Mill Creek at 87th Street Lane (MI4)
Introduction
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.
Figure 1. Streams, municipalities and site locations in the Mill Creek watershed.
Figure 2. Land use in the Mill Creek watershed.
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.
Streambank erosion, Little Mill Creek,
Lenexa, KS
The Kansas Department of Health and Environment (KDHE) lists suspended
sediments as the cause of biological impairment in the Mill Creek
watershed. Suspended sediments are also directly correlated to
indicator bacteria populations, which KDHE also has found to cause
impairment in the Mill Creek watershed. While suspended sediments are a
known cause of degradation in Mill Creek basin, best management practices,
such as erosion control fences, grass buffers, and riparian area buffers
have been implemented in select parts of the basin to control these
sources of sediment. To view a list of Mill Creek impairments, enter
“Mill Creek” as the water body name and “Johnson County” in the
county dropdown at the following website: (KDHE)
Rill development on construction site,
Clear Creek watershed.
Purposes
The USGS, in cooperation with the Johnson County Stormwater Management
Program, is conducting a study to characterize the magnitude and sources of suspended
sediments in the Mill Creek watershed.
Specifically, the study will
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Estimate concentrations and loads of suspended sediment at 8 sites within
the Mill Creek watershed.
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Estimate sources of suspended sediment using chemical tracer
techniques and stormflow sediment dynamics.
Storm sampling, Mill Creek at Johnson Dr, Shawnee, Ks
Approach
Water-quality and stage sensors are operated at 9 sites (Figure 1) in
the Mill Creek watershed. Water quality sensors continuously (every 5 minutes)
measure:
1.
Gage height (depth below stream surface)
2.
Specific conductance (electrical charge carried by streamwater)
3.
Water temperature, and
4.
Turbidity (murkiness of the water)
Data
are used to estimate streamflow and suspended-sediment transport during
stormflow conditions.
Instantaneous measurements of streamflow and
suspended sediment concentration are statistically related to continuous gage
height and turbidity measurements in order to model streamflow
and suspended sediment concentration every 5 minutes at all 9 sites (
Figure 3).
Benefit
This study will characterize subwatersheds/land uses which are the
dominant sources of suspended sediments in the Mill Creek basin. The
information will be used by the Johnson County Stormwater Program to aid in
the implementation of BMPs to decrease sources of sediment to the stream.
Gage height, turbidity, and specific conductance
during storm runoff,
5/2/06-5/4/06,
Little Mill Creek at Lackman Rd.
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WATER DATA & STUDIES
U.S. Department of the Interior |
U.S. Geological Survey
