Workshop Item -Megan Hedstrom, Stormwater Coordinator
Title
Stormwater Inspection and Maintenance Programs
Executive Summary
The Minnesota Pollution Control Agency (MPCA) issues the City its Municipal Separate Storm Sewer (MS4) Permit and is the regulatory agency that sets criteria for inspection and maintenance activities. The permit requires inspection maintenance on the city’s stormwater facilities on a five-year cycle.
Staff will describe the current activities conducted to meet these requirements and the potential impacts on our residents. In 2022, staff conducted outreach, facilitated conversations and meetings with residents, and began the first round of pond maintenance under this newly revised program. Results, including success stories and lessons learned, will be presented to Council.
Background
A presentation on the full scope of this program was given at the March 21st workshop. Staff’s proposal, beginning in 2023, each year, is that inspections on the scheduled year’s pond system will begin in January. In March, a summary report of all pond inspections will be assembled by Public Works staff and provided to the engineering department to begin outreach and education on upcoming maintenance needs. Pond specific issues and concerns will be addressed over the spring months, with the aim of being able to mobilize to the ponds and conduct the necessary maintenance work beginning in July.
In order for Public Works to maintain a body of water, the pond buffer zone must remain accessible and clear of obstructions wherever possible. Some examples of items that would require maintenance are trees and brush leaning over the pond, dropped limbs that are impeding flow of water, trees or brush leaning over fences and encroaching onto adjacent property lines, and the type and condition of trees growing in the buffer. Efforts are made wherever possible to preserve healthy native trees, such as oaks, maples and pines. Additionally, inspection will be done on the culverts that carry water to and from the ponds. These areas must remain free of all tree and brush growth to reduce risk of clogging.
This activities need to be performed for the pond to continue to function as it was originally designed. These assets were built with the neighborhoods for two purposes: water quantity control and water quality control. These ponds provide storage for rain water during large rain events to prevent flooding of homes. If culvert’s are clogged with fallen sticks and leaves from the trees, or if tree roots have grown into the culverts, water will not flow through the pipe system as it is designed to which can have flooding impacts not only on neighboring properties, but many properties upstream of the issue. Staff are starting to see the impact of deferred maintenance of these ponds when we receive large rain events. We receive more nuisance calls of water rising extremely high due to non-functional culverts and pipe systems.
In addition to providing water quantity, or flood control, these ponds were also designed to serve a water quality purpose. The first major flush of rain water carries debris from streets, yards, and the pond buffer into the pond. Once in the pond, pollutants sink to the bottom of the pond where they remain, which means that less pollutants are traveling downstream to regulated waterbodies. These ponds were designed with native grass buffers, that help trap pollutants running down the shoreline. Now, many of these pond buffers have filled in with willows and buckthorn which drop a lot of limbs and leaves into the pond. There’s only so much space at the pond bottom for pollutants to be held. When the pond bottom fills up, it will need to be dredged, or re-dug to the original pond bottom. It is significantly more expensive to remove tree debris once it’s settled to the bottom of the pond than it is to remove the trees from the shoreline.
Prior to beginning work, educational materials are sent to property owners bordering the affected ponds. An example of these materials is attached. These notices are sent out a few weeks prior to beginning work to initiate conversations on the proposed maintenance to work to lessen the direct impact to neighboring properties when possible. Details on how final maintenance decisions are made and photos of what this looks like will be presented to Council at this workshop.
Staff Recommendation
Staff is asking for feedback from the City Council on the program.
Attachments
1) Generic Stormwater Brochure
2) Pond Specific Example