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Public Works

Project Overview -- 18th Street SW Regional Detention Basin

The City of Cedar Rapids is transforming a 3.5 acre parcel located adjacent to 18th Street SW into a regional detention basin. The majority of this land (2.43 acres) was acquired by the City in 1999 to be used for stormwater management. The regional detention basin is engineered to capture runoff generated by a 100-year storm event from 94 acres of land. This basin will help address stormwater runoff issues that are impacting areas of the city between the location of the basin and the Cedar River. Construction on the basin began in June 2017 is scheduled to be completed by the end of August 2017.
Detention Basin Plan

Frequently Asked Questions
Why is the City building one large regional detention basin instead of having developers construct smaller detention basins for their sites?
What steps were taken to gather public input?
This area is home to a wide variety of wildlife. What was done to protect them?
Will wetlands disturbed by this project be restored?
Why were so many trees removed?
The trees and wetlands offered water quality benefits. How will the basin provide these same benefits?
Why was the existing pond not incorporated into the design for the basin?
Why were the fish in the pond not relocated before construction?
Were citizens ever allowed the opportunity to purchase this property?
Why wasn’t the detention basin designed to provide stormwater management while being an attractive amenity for the neighborhood (a pond with public access, fishing, walking trails, etc.)?

Why is the City building one large regional detention basin instead of having developers construct smaller detention basins for their sites?

The City’s stormwater master plan indicates that regional detention basins are often more effective at managing stormwater runoff than several smaller basins. The use of a regional detention basin makes it possible for several development areas to be served by one larger basin. This is a regional basin that provides stormwater storage to mitigate runoff from about 94 upstream acres – residential and commercial development. Some of these developments have never been associated with any detention because they were developed prior to the City requiring detention for private development. In order to capture stormwater properly, detention basins also require regular maintenance. Maintaining one larger regional detention basin is simpler and more efficient than caring for several smaller basins.Drainage area

What steps were taken to gather public input?

Since 2014, City staff have met with various property owners adjacent to the regional detention basin project site. These meetings have been informal and formal with the last formal public meeting held March 8, 2016. During this March 2016 meeting, the design plan for the detention basin was shared and property impacts were discussed with those in attendance. An invite to attend that public meeting was sent to all property owners with land directly touching the City-owned property where the detention basin is being built. These property owners are deemed to be the most directly impacted by this project, and their input on what the finished basin looked like was a critical stage in the project planning process.

The public hearing for the project was held on January 24, 2017, and bids were received on February 1, 2017. No public objections were filed. Construction on the basin is scheduled to be completed by August 2017.

Presentation Shared at March Public Meeting
FAQ List

This area is home to a wide variety of wildlife. What was done to protect them?

These design plans were developed with strict oversight from the Army Corps of Engineers and Iowa Department of Natural Resources (IDNR). These organizations are the regulatory agencies for projects that impact wildlife and natural features like streams or wetlands. All of their recommendations to limit the environmental impact of this project are being implemented. Native grasses and wildflowers (including a large array of pollinators) will be planted within the basin and 30 new trees will be intermixed with 43 existing trees surrounding the basin to provide additional habitat for wildlife.
FAQ List

Will wetlands disturbed by this project be restored?

Because wetland in this area will be disrupted by this project, an area in Seminole Valley Park will be used as a wetland to minimize the environmental impact. This work is under permit with the Army Corps of Engineers which oversees any project where wetlands are disturbed. When the mitigation is completed to the standards set forth by the Army Corps of Engineers, there will be more wetland area created than what was present on the construction site. Our desire is always to replace or replenish environmental features during the course of these necessary construction projects.
FAQ List

Why were so many trees removed?

The new basin will occupy nearly all of the land on this parcel. The City was able to save 43 trees along the perimeter of the property, and the others were removed to accommodate construction of the detention basin. Having trees within the detention basin reduces stormwater capacity and can undermine the integrity of the basin. Because the trees removed for this project were deemed by the City’s design consultant to be of low-quality, the City was not required to re-plant any trees as part of this project. However, the City has elected to plant 30, high-quality trees around the edge of the basin to provide additional natural qualities for the area.
FAQ List

The trees and wetlands offered water quality benefits. How will the basin provide these same benefits?

The bottom and sloped sides of the basin will be planted with native grasses and wildflower seed. These plants will serve as natural filters for any stormwater runoff, encouraging infiltration. The wetlands disturbed by this project are being reestablished both on and offsite per the specifications of the Army Corps of Engineers. When the mitigation is completed, there will be more wetland area created than what was present on the original construction site. All of these factors will offer water quality benefits.
FAQ List

Why was the existing pond not incorporated into the design for the basin?

A man-made pond was built on this property in the early 1990s before the City acquired the property. Over the years, citizens elected to stock the pond with fish and use the area for fishing and recreation. However, this property was never designated to be public park or recreation space. In order to accommodate runoff for a 100-year storm event, the floor of the new basin will be significantly lower than the existing pond and as a result the City needs to excavate the existing pond footprint to provide enough storage for the basin. The pond was drained the week of June 5, 2017.
FAQ List

Why were the fish in the pond not relocated before construction?

Upon consultation with the Iowa Department of Natural Resources (IDNR), the City was instructed that the fish shouldn’t be moved to limit the risk of spreading disease.
FAQ List

Why wasn’t the detention basin designed to provide stormwater management while being an attractive amenity for the neighborhood (a pond with public access, fishing, walking trails, etc.)?

To hold the required amount of runoff, the basin will occupy nearly the entirety of the City-owned parcel. The basin will be dry most of the time so it has the capacity needed to capture high volumes of runoff during a storm event. The parcel is surrounded by privately owned land with no existing public access points. There will be a graded ledge around the top of the basin, and with support of the neighbors, the City could evaluate the possibility of converting that into a walking trail in the future.
FAQ List

Were citizens ever allowed the opportunity to purchase this property?

Knowing the value of the pond to the neighborhood as an amenity (even though it’s not an official park), the City did offer to sell the pond to adjacent property owners on two occasions. The proceeds from the sale of the pond would have be used to purchase additional land to the north of this site in lieu of the pond’s footprint for stormwater detention.  The property owners did not make an offer to purchase the property.
FAQ List

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