Iowa eyes new garden to fight erosion at governor’s mansion

Terrace Hill is the Iowa governor's mansion. (Photo by Perry Beeman/Iowa Capital Dispatch)

Iowa state government’s campaign to cut erosion on state properties, already underway at the Capitol, may be heading to the governor’s mansion, Terrace Hill.

The Iowa Environmental Protection Commission on Tuesday will consider a $40,000 plan to design and engineer an enhanced rain garden right outside the main visitor entrance of the mansion along Grand Avenue west of downtown Des Moines. 

The contract with the Iowa Department of Administrative Services would be similar to one that is already in effect at the Capitol. There, the state is spending about $200,000 to install bioretention cells along the terraced areas on the Capitol grounds. Those soak up water and slow the flow to reduce erosion. 

The issue at Terrace Hill was reported to DNR by Diane Becker, Terrace Hill administrator, said Steve Konrady, project officer for the Iowa Department of Natural Resources. 

Becker had noticed some moderate erosion near the public entrance, just off a parking area usually restricted to pedestrians.

Konrady said water is running off the west-side parking lot that was expanded in recent years and from the mansion’s roof. Heavy rains send water through an eight-inch pipe into the yard, where grass is having trouble growing. There were signs of soil erosion, but nothing major yet, he added.

The administrative services department and DNR discussed a project that would both solve the problem and create a garden. Signs would educate visitors on the use of rain gardens and other techniques to slow water down and reduce erosion on urban lands. 

It’s hard to say how much the installation will cost, but DNR has federal environmental grants that can cover the work, Konrady said. The planning, expected to take six months, would cost up to $40,000 if the environmental commission approves the contract. The installation would likely be sometime next year.

The National Park Service and state historical officers would have a hand in approving the work due to Terrace Hill’s status as a historical monument.

The damage is relatively minor so far, DNR reported.

“It isn’t dangerous, but it’s unsightly,” Konrady said of the erosion. If it the problem isn’t fixed, the runoff could buckle sidewalks and damage retaining walls, he added.

The project likely will combine a rain garden with underground storage that would send overflow to another pipe outlet further down the sloping front yard of the mansion, Konrady said.

If this demonstration project is successful, the state might pursue gardens in a couple of other spots on the grounds where water runs rapidly down the hill, Konrady said.

The mansion is, of course on a hill. Konrady said neighbors in that area have often fought erosion on the rolling terrain north of the Raccoon River.

The state installed similar stormwater projects at Marble Beach State Park at Spirit Lake, Pleasant Creek State Recreation Area near Palo and Rathbun Lake near Moravia. The funds come from a U.S. Environmental Protection Agency program to fight runoff pollution.