Polk County presents Walnut Creek floodplain assessment to Urbandale; recommends prairie, woodland and oxbow work

Polk County water resources staff presented a Walnut Creek watershed floodplain assessment to the Urbandale council and recommended a menu of projects — including prairie restoration, woodland understory management, targeted stream restoration and oxbow/wetland enhancements — that the county says could help Urbandale meet five‑year WMA goals for stormwater storage and floodplain restoration.

Kristen introduced Cassie Juul and Robert Austin of the county water resources team to present the assessment, noting County staff had performed a visual inventory and integrated prior local studies. Cassie said a large portion of the urban Walnut Creek watershed falls within Urbandale and that the city therefore has "responsibility and opportunity to have some large impacts within the watershed." The county said the WMA set quantifiable five‑year targets for Urbandale of roughly 25 acre‑feet of on‑land water storage and about 80 acres (or ~6,500 linear feet) of floodplain/stream restoration.

Presenters prioritized work on city‑owned parkland to minimize land‑acquisition hurdles. Recommended low‑cost, high‑return actions include prairie restorations at identified sites in Walnut Creek Regional Park and woodland understory restoration across a roughly 57‑acre oak savannah by removing invasive honeysuckle and reestablishing native understory plants. The county suggested park maintenance staff could lead many of these efforts with county technical support.

The consultants called stream restoration the most challenging option because of tight urban corridors, potential tree removal and limited traditional funding streams, but they identified a couple public‑property reaches where bank stabilization and restoration could be feasible if funding and permitting align. For water‑quality and storage benefits, the assessment also recommended wetland types (stormwater wetlands, pumped wetlands and oxbow enhancements) to hold runoff and filter pollutants; the appendix lists likely grant programs and funding sources and includes cost estimates.

Council members asked about grant timing. Cassie said several relevant programs open annually (for example, the Iowa DNR water quality initiative grant typically solicits applications from late fall to early winter) and that grant cycles often require a one‑year implementation horizon. When a council member noted some parkland and Waterford Road lie in Dallas County, Polk County staff said watershed initiatives routinely cross county lines and that Polk County intends to target headwaters in adjacent counties where it will achieve the greatest downstream benefit.

Polk County described services it can provide to Urbandale, including grant writing, engineering and construction oversight, and vegetation establishment and maintenance expertise. Presenters recommended starting with oxbow enhancements and woodland understory work as "low‑hanging fruit" that could meet WMA goals quickly and leverage recurring grant windows. The county pledged follow‑up support and a menu of priority projects with cost estimates; council members requested additional details and next steps for funding and implementation.

Next steps: Polk County staff offered to provide detailed project scopes and connect Urbandale to grant opportunities and county implementation resources; council and staff will review the assessment appendix and consider projects that can be matched to park maintenance capacity and funding timelines.