Stormwater Management an Important City Function

City Engineering Department Oversees Stormwater Management

When it rains, the management of stormwater is not something on the forefront of most residents’ minds, but for the City of Marshfield Engineering Division, it is an important element of their job to make sure that the water hitting the ground in the community leaves it as clean as possible.

As a Phase II community (based on EPA designation as an urbanized area with of at least 10,000 population or a density of 1,000 people/square mile, and classified as part of the Wisconsin River watershed) and a Municipal Separate Storm Sewer System (MS4) permitted community, the City must submit an annual report outlining their plans for stormwater management and release to meet stormwater discharge guidelines set by the Wisconsin Department of Natural Resources (WIDNR).

Separate from the wastewater system (which handles sanitary sewer that flows from homes), stormwater management handles precipitation (rain, snow, hail, sleet).

For example, a raindrop that lands on the clinic/hospital campus runs off a building or parking lot and makes its way to one of the neighboring city streets. There, it is collected in a catch basin, which has a sump to help removed some of the total suspended solids (such as dirt or gravel). Then, the raindrop travels into a pipe that is part of the city’s 103-mile stormwater piping system, making its way downstream until it ultimately reaches the Walnut Detention Basin.

One of 100 plus detention basins in the community, these basin areas are designed to limit how much water is released into the stormwater system at any given time. If stormwater flows are greater, rainwater is coming down faster than the pipe system can handle, these basins are systematically designed to collect, store the excess stormwater, and limit the volume entering the system, allowing water to enter (in this case, a single 24” pipe) at a controlled flow rate weight. This prevents flooding of properties and protects the system from becoming overwhelmed.

Originally constructed in the 1970’s, the Walnut Basin was redesigned in 2006 from a stormwater pond to a stormwater management pond, which helps clean the water instead of just storing it.

Consisting of three ponds, water enters the basin into one pond (known as the forebay) which takes out larger particles, then it flows in a zigzag pattern before exiting the basin, which helps remove more of the solids. Total Suspended Solids (TSS) are solids in water that can be trapped by a filter, and can include a wide variety of material, such as silt, decaying plant and animal matter, industrial wastes, and sewage

“It gives more time for solids to settle,” said Tom Turchi, City Engineer. “Then the water leaves cleaner.”

When the water leaves cleaner, it is more environmentally-friendly as there is less sediment carried into streams and lakes. Additionally, it reduces stress on the piping, which gives it a longer lifespan.

“Right now, if you take a look at Castle Rock and Petenwell along the Wisconsin River, there is enough sediment and phosphorus released from the watershed that the lakes are somewhat unusable at the end of the season, due to blue green algae caused by an excess of phosphorous” said Turchi.

Positioned at the highest point of all three area watersheds (Yellow River, Mill Creek, Eau Pleine), Marshfield has its own benefits and challenges pertaining to stormwater management. With clay making up a significant part of Marshfield’s soil, there is not as much infiltration through soil into storm water, with most of the contamination coming from runoff.

In Marshfield, there are approximately 100 stormwater basins, both public and private, located within the city, and therefore flooding is typically localized (wet yards), not affecting structures.

Stormwater Drainage. Read more:

After leaving the basin, the raindrop that falls on the hospital campus eventually ends up traveling into Squaw Creek, then to the Eau Pleine Reservoir, then into the Wisconsin River.

The stormwater management plan system is designed with help from a consultant, with historic weather patterns and other factors being examined. All of this is outlined in a Storm Management Plan, which is updated every few years.

“It’s basically a model of the entire city with various classifications. We determine what we have in place and what we could build to reduce the total amount of TSS while looking for the best bang for our buck,” said Turchi. “Ultimately, when the plan is completely done, it gets approved by the EPA and the DNR administers it under federal law.”

An important aspect of Stormwater Management is Stormwater Quality. Regulated by the DNR and EPA, the total suspended solids (TSS) leaving a city are carefully monitored for elements such as phosphorus levels. The goal is for Total Maximum Daily Loads (TMDL) to have phosphorus levels at the same level as they were before human habitation. Ultimately, when the TMDL plan is completely done, it gets approved by the EPA and the DNR administers it under federal law.

Another key part of the plan is maintenance and rehabilitation of the piping underground. Street sweeping is an important element of this. Working with the City Street Division, more than 2,700 lane miles were swept in the City in 2016 alone. The Division also cleans the catch basins that trap suspended solids and carefully monitors the use of salt during the winter.

Already regulated by a City Ordinance, residents are reminded to keep grass clippings out of the streets.

“In the long term, when you look at everything we can do to help with the environment downstream and keep our rivers and streams clean, it ultimately allows our children to enjoy a cleaner, better environment,” said Turchi.

News Desk
Author: News Desk