Holton Stormwater Stabilization Project
What it is:
A stabilization project to address erosion occurring in a stormwater drainageway located in a neighborhood in southwest Holton, KS. Overall goals of the project are to reduce erosion and stabilize the channel of the drainage ditch and improve the quality of water delivered to Banner Creek by the drainageway.
An educational program developed as a companion program to the stabilization project has resulted in the installation of numerous rain gardens and rain barrels in the city. Educational signage identifying and explaining stabilization practices will also be installed utilizing educational program funding following completion of the stabilization project in 2013.
What has been accomplished so far:
Project designs have been completed, funding has been secured, cooperative agreements with the City of Holton and Jackson County has been acquired, and agreements have been signed by the majority of property owners along the length of the stormwater drainage. As of February 2013, a volunteer contractor has starte
Why this project is needed:
Runoff from city streets, rooftops, sidewalks and other "hard" surfaces in the watershed area above the project area is quickly conveyed into stormwater drains. Even after small rains, large quantities of runoff can accumulate, creating the potential for erosion. The runoff also picks up pollutants (street salts, oil, pesticides, fertilizers, pet wastes and more) along the way, carrying it into receiving streams and impairing water quality.
Stormwater collects from an area of southwest Holton (approximately 50 acres in size) and is conveyed to an outlet point near the junction of Nebraska and W. 3rd Streets. Here the stormwater “daylights” (comes aboveground) in a lot owned by the City of Holton. From here, stormwater flows southward through privately-owned backyards for approximately1,500 feet before entering the receiving stream, Banner Creek. The large volume of runoff and steep slopes cause significant erosion through sections of the neighborhood. The erosion endangers city utilities, threatens several structures, and has caused significant damage to private property.
Positive outcomes expected:
The stabilization project will significantly reduce the amount of erosion occurring along the length of the stormwater ditch from 3rd Street southward to Lilac Drive, as practices designed to slow flow velocities and hold soil in place are installed. Significant water quality improvements are also expected as a result of installation of bioretention practices. Bioretention is accomplished through the capture and retention of stormwater runoff in a treatment areas such as a grass buffer strips, rain gardens, rain barrels or bioretention cells. Water pollutants and sediment in the runoff are removed as it passes through vegetation or captured in a shaped area that is planted to deep-rooted vegetation. Stormwater volume is also reduced through infiltration into the soil, transpiration by vegetation and through evaporation. The velocity of stormwater flows is also reduced by vegetation and bioretention structures, which further reduces the erosive force of downstream flows.
Water quality improvements expected from implementation of this project will be greatest after smaller rainfall events. Heavy rains that produce large volumes of runoff in a short period of time cannot be treated as effectively as smaller rainfall amounts, as large stormwater events are likely to overwhelm bioretention features. However, some mitigation of runoff volume and improvement of water quality is expected for any sized rainfall event.
What practices are being used:
Culverts located under four city streets along the course of the stormwater ditch act as grade control points. This creates flow and erosion conditions as well as other characteristics that are unique within each block. As a result, erosion in one city block sections may be relatively minor, and in the block section below it may be severe, followed by a block section that actually experiences significant deposition of eroded material from the block(s) above.
The project design calls for practices which address the unique circumstances and slopes found within each city block. Bioretention practices include a large bioretention cell to be installed in the city lot located at the head of the ditch where stormwater first “daylights” (near the junction of Nebraska and W 3rd Streets). This structure will be planted to native vegetation. A series of rock cross vanes will be installed at strategic locations along the length of the ditch to stabilize the channel bed and help to “step down” stormwater flows. The sides of the drainageway will also be re-sloped and planted to native vegetation, with rock and other hard structures to be installed along the channel edges in strategic locations to stabilize and armor the bank against erosive flows.
The majority of the project will be constructed by a hired contractor. Volunteers will plant the vegetation and a local contractor has volunteered to construct the bioretention cell on city property. The project is slated for completion in 2013.
Funding and Technical Assistance Sources:
Funding and technical assistance are being provided by the following: