Stormwater Management

Flood-Inundation Mapping & Model of Muddy Creek 

The U.S. Geological Survey (USGS), in cooperation with the city of Harrisonville, Missouri, assessed flooding of Muddy Creek resulting from varying precipitation magnitudes and durations, antecedent soil moisture conditions, and channel conditions. The precipitation scenarios were used to develop a library of flood-inundation maps that included a 3.8-mile reach of Muddy Creek and tributaries within and adjacent to the city.

Muddy Creek flood map

The hydrologic and hydraulic models were calibrated to the September 28, 2019; May 27, 2021; and June 25, 2021, runoff events representing a range of antecedent moisture conditions and hydrologic responses. The calibrated HEC–HMS model was used to simulate streamflows from design rainfall events of 30-minute to 24-hour durations and ranging from a 100- to 0.1-percent annual exceedance probability. Flood-inundation maps were produced for USGS streamflow stages of 1.0 feet (ft), or near bankfull, to 4.0 ft, or a stage exceeding the 0.1-percent annual exceedance probability interval precipitation, using the HEC–RAS model. The consequence of each precipitation duration-frequency value was represented by a 0.5-ft increment inundation map based on the generated peak streamflow from that rainfall event and the corresponding stage at the Muddy Creek stage reference location.

Seven scenarios were developed with the HEC–HMS hydrologic model with resulting streamflows routed in a HEC-RAS hydraulic model and these scenarios varied by antecedent soil-moisture and channel conditions. The same precipitation scenarios were used in each of the seven antecedent moisture and channel conditions and the simulation results were assigned to a flood-inundation map condition based on the generated peak flow and corresponding stage at the Muddy Creek reference location.

Click here to view the Muddy Creek flood-inundation map and model.

Click here for additional information and about the project and the scenarios that were studied.

What is Stormwater?

Stormwater is the runoff from rainfall and snowmelt. In undeveloped areas of Cass County, such as pastures, grasslands, forest, and other natural areas, much of the rainfall and snowmelt soaks into the ground. Vegetation helps to slow runoff, allowing the water to seep into the ground. In urban areas, however, buildings, streets, parking lots, sidewalks, and other impervious surfaces do not allow water to soak into the ground. This causes both increased amounts of runoff and faster flow. Along the way, runoff can pick up pollutants such as fertilizers and pesticides from yards, motor oil from leaking cars, pet waste, and loose soil from construction sites. This can cause downstream waterways to become choked and polluted. Stormwater drainage systems then become important tools to protect the quality of our water and prevent flooding.

What is Stormwater Management?

Stormwater management is the process of controlling and processing runoff so it does not harm the environment or human health. It is an important tool used to prevent water pollution.

How does Harrisonville manage its Stormwater?

Harrisonville has a Municipal Separate Storm Sewer System (MS4) which is any system where the stormwater is conveyed separately from the sanitary sewer system. A great variety of natural and manmade structures and landforms are used to construct an MS4. These may include inlets, pipes, earth berms and ditches, box culverts and catch basins, grass or concrete channels and culverts under roadways. Any of these structures can be used to carry stormwater out of developed areas of our city.

In Harrisonville, the stormwater management program is part of the Public Works Department. Email Carl Brooks, Director of Public Works, or call 816-380-8964.

The Harrisonville Public Works Department wants to share with you this important reminder from our friends at St. Louis MSD Project Clear about what should and shouldn’t be flushed down your toilet.

Additional Resources

Learn more about stormwater management and the need to protect our watershed with these educational materials.