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Park may help curtail flooding; City engineer suggests basin in Pedersen Valley
by Rick DeClue · News · September 18, 2014
Citizens of West Branch packed the city council chambers Monday to talk about potential changes in stormwater runoff caused by developing the proposed park in Pedersen Valley.
The properties most affected would be homes on Scott Drive that abut the proposed 18-acre park at the southern end.
The key to the concept plan for the park is the creation of a 62,459-cubic-foot retention pond on the southern end of the park. A 15-inch outlet pipe would control the release of water from the retention pond and direct it to a creek north of the homes on Scott Drive.
According to estimates prepared by West Branch city engineer Dave Schechinger of Veenstra and Kimm, this retention pond would create a stormwater release rate nearly 88 percent less than the current farmland or if it were developed like the rest of Pedersen Valley.
Pat Nagel of 212 Scott Drive said of the rainfall coming down the watershed, “every drop lands in our back yards. It’s a bowl. Water won’t sit in a retention pond.”
Mayor Mark Worrell said the park development would include moving a lot of soil. State law requires the retention pond to hold water on site.
Cost estimates for the park development show the city spending nearly $1 million on earth work and grading for the park.
Schechinger said one challenge is the amount of soil being moved around the park site or brought in and compacted. This initially reduces the ability of the soil to absorb water. Planting prairie grass on flood plain contained in the park site will help moderate the flow of stormwater. The retention pond helps with the stormwater volume by controlling the release rate.
Gary Bass of 228 Scott Drive referred to several storms over the past few years that flooded back yards on his street.
He also asked how the city could put the retention pond over the oil pipelines running under the site.
Brian Boelk pf HBK Engineering, which developed the concept plan, said the retention pond will sit outside the easements for the pipelines.
Nagel said he had to spend a lot of money to have their property removed from the Federal Emergency Management Agency 100-year flood plain. She said additional drainage might put them back in that category.
Schechinger said FEMA’s flood boundaries would not be affected by the park development.
To demonstrate the effect of the park, Schechinger presented a chart showing several potential uses of the land:
• “as is” — vacant farmland
• “as planned” — ball fields, recreation center and other park features in current concept design plan
• developed as residential — standard measurements
• developed as residential — similar to existing sections of Pedersen Valley, i.e. lower density.
Building 33 to 39 homes on those 18 acres would produce about the same runoff as farmland, which it is now, Schechinger said.
Or, if you build 45 homes, instead of a park, that would increase runoff by 6 percent. Building a park would increase current runoff by 9.6 percent.
Schechinger said using permeable pavement, but not draining the baseball fields, would lower that figure to 2.4 percent. However, Schechinger said it is a good idea to drain the ball fields.
Installing a retention pond in the park would mean significantly less runoff than ever before, he said.
Schechinger pointed out that the concept plan and the retention pond are not intended to address existing water flows north of Orange Street. They are designed to show that the development of the 18-acre parcel will include stormwater management for the park improvements.
A third speaker, Stephen Marlow, addressed the need for the city to be a “good neighbor.”
Marlow is the vice president and chief financial officer of Care Initiatives, which operates the Crestview Nursing and Rehabilitation Center.
He wants buffering and lighting to minimize the park’s impact on Crestview residents, as well as reasonable hours of operation for the park.
Worrell assured Marlow that the city would work with Care Initiative’s engineers to address those issues, and agreed the city needs to be a good neighbor.
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