Flag Pole Park (PDF), located just off Highway 46 on the north end of town, is the site of Amery’s latest water quality improvement efforts. The excavation is part of a 2-phase stormwater improvement project to collect and pre-treat water from the city’s storm sewer system before it discharges into North Twin Lake.
Up until now, the runoff water from this sub-watershed was drained directly into North Twin via storm sewers. As it flows over the ground surface, though, this runoff water collects sediments and nutrients that are then deposited into the lake. In significant quantities, these elements can be detrimental to lake water quality.
The runoff water from this drainage area is high in total sediment and causes significant phosphorus loading. Of the 13 sub-watersheds that drain to North Twin Lake, the Flag Pole Park area ranks number 2 for annual sediment and phosphorus contributions on a per-acre basis. For this reason, the project location was identified as a hotspot for consideration of a runoff reduction practice in the city’s Stormwater Management Plan.
The Stormwater Management Plan was completed in February 2009 and
prepared by Short Elliot Hendrickson (SEH), Inc. in cooperation with the
City of Amery, the Amery Lakes Protection and Rehabilitation District,
Harmony Environmental, Inc., the Wisconsin Department of Natural
Resources, and the Polk County Land and Water Resources Department. SEH
Inc. is also the engineer for the stormwater improvement project at Flag
excavation phase of the project is now underway to redirect and settle
runoff water from this sub-watershed of North Twin Lake. All but 1 of
the culverts under Highway 46 have been removed or plugged, and a silt
curtain has been installed at the outlet of the remaining culvert to
prevent sediment from entering the lake. Storm sewer inlets have now
been replaced and rerouted to drain into a series of 3 constructed pond
cells, which will pre-treat the water to remove sediments and nutrients,
such as phosphorus.
Since the groundwater level at the project
site is high, the water storage capacity of the soil is limited. The
constructed ponds, however, will provide significant water storage, with
a combined capacity of 703,169 gallons. The system will also regulate
discharge of the pre-treated water from the ponds into North Twin Lake.
The project’s 2nd phase will be to re-vegetate the area with native
shrubs, trees, and plants. Native species are well adapted to the local
climate and are integral parts of the local ecosystem. Their deep root
systems will likewise encourage infiltration and prevent erosion.
Planting is expected to begin after Labor Day and the park’s namesake,
the flagpole, will be reinstalled following the project’s completion.
Funding for the project comes from a Lake Protection Grant from the
Wisconsin DNR. The state is providing 75 percent of the funds while the
Amery Lakes Protection and Rehabilitation District is covering the
remaining 25%, with in-kind service from the City of Amery and the Polk
County Land and Water Resources Department.