Stormwater Management

Removal of the parking garage in the North Gateway also reduced the amount of toxic runoff in the area and now helps mitigate the impacts to water quality in the Mississippi River. Built in 1986, the parking garage did not have the devices in place to capture oils and heavy metals typical of runoff from vehicular pavements that are required today. The replacement of this large impervious structure with a new green space reduces the amount of runoff for the area and allows water to be absorbed and filtered through the soil.

• During the construction on the grounds, several new sustainable stormwater structures were installed, including:
• A new irrigation system that can shut off on its own if a line breaks or if the ground is wet from rainfall
• Two underground retention tanks separate silt and excess nutrients before releasing the water into one of the two reflection ponds
• A 37,000 gallon retention tank in Luther Ely Smith Square that filters out silt and nutrients from the water, which is then reused in the irrigation system
• A native rain garden at the ranger station that allows runoff to be absorbed and filtered through the soil
• Bioswales around the reflection ponds that help to absorb excess water, filter our pollutants, and reduce the likelihood of algae blooms
• New moisture meters will be installed that will direct the irrigation system to turn off and on accordingly

All of the new soils added to the park grounds are structural soils, which help to reduce compaction and runoff while allowing for absorption and promoting root growth. Additionally, permeable decomposed granite was added in the sitting areas in Luther Ely Smith Square and on each side of the new entrance to the Visitor Center and Museum along the north-south walkway, reducing runoff by allowing water to flow into the soil below.