When it rains or snow melts, much of the water—referred to as stormwater—runs off hard surfaces such as roofs and pavement from neighboring urban areas and flows into the Arboretum. One of the biggest challenges we face in managing Arboretum land for native biodiversity and functioning ecosystems is the influx of stormwater.
The Arboretum’s 1,200-acres lie within two different watersheds. Approximately 1,050 acres are in the Lake Wingra watershed, which drains into Lake Monona via Wingra Creek along the Arboretum’s eastern edge. The other 150 acres (in the southwest part of the Grady Tract) are in the Lake Waubesa watershed and drain into the lake via Nine Springs Creek and Upper Mud Lake. Stormwater makes its way to the Arboretum from as far away as Westgate Mall and University Research Park.
Overall, approximately 1,400 acre-feet (almost 470 million gallons) of stormwater enters the Arboretum at ten different points annually. An acre-foot is the amount of water needed to cover one acre with a foot of water—by that measurement the Arboretum receives enough stormwater to cover its 1,200 acres with over a foot of water each year!
The water carries large amounts of sediment and nutrients such as nitrogen and phosphorus into the Arboretum. Engineered stormwater ponds, called detention ponds, were built decades ago in several locations to manage water flow and capture sediment and nutrients. Whatever is not held in the pond can be carried downstream and deposited in the prairies and wetlands.
When they settle in natural ecosystems, the sediment and nutrients often alter growing conditions and make them favorable to aggressive invasive species such as narrow-leaved cattail and reed canary grass, which can quickly form dense stands and push out native species. These are some of the most stubborn invasive species we have to manage, and the wet prairie and wetland areas where they grow are among the most challenging to restore.
In addition to sediment and nutrients, a discouraging amount of trash washes into the Arboretum. Dozens of forty-gallon bags have been filled with garbage from each of the ponds the last several years. Other routine maintenance is also required to keep the ponds functioning properly. After each major rain event we clean off inlet and outlet grates and weirs so the water can flow into and drain out of the ponds. This can take the entire crew several hours for each event—a considerable amount of time that takes away from other restoration activities.
Erosion and washouts can also result from extreme rain and snowmelt events, when the volume of water flowing from the surrounding urban landscape overwhelms the Arboretum’s stormwater infrastructure. A concrete flume (chute) that was built to carry water from the Beltline area into Curtis Pond collapsed decades ago. With no functional way to channel the water, major erosion has resulted.
In the southern Grady Tract, stormwater flowing from the Dunn’s Marsh neighborhood has washed out service lanes and undercut the boundary fence in several places. The service lanes east of Curtis Prairie have also suffered severe flooding and erosion over the last several years, making it more difficult for the crew to access work sites and for visitors to enjoy the trails for hikes and runs.
The Arboretum receives much more water than it did in the past due to urban development of the surrounding landscape. To exacerbate the issue, extreme rain and snow events have become more frequent over the last fifteen years—a trend we assume will continue as the climate changes. The work our crew puts into stormwater management, from pond maintenance to managing invasive species, is considerable. We expect the resources we will need to address these challenges will continue to grow, too.
Stormwater management is a community challenge and a number of partners work with the Arboretum, including other University of Wisconsin departments, the cities of Madison and Fitchburg, Dane County, Wisconsin Department of Transportation, Wisconsin Department of Natural Resources, private contractors, and non-governmental organizations.
There are also ways residents, organizations, and workplaces in the surrounding urban landscape can help reduce the volume of stormwater and improve the overall quality of our water. Some approaches include: cutting back on impervious surfaces where possible, installing rain gardens where suitable, using rain barrels to capture water running off roofs, reducing fertilizer use, using less salt in the winter, keeping storm drains clear of leaves and other debris, and picking up litter.
For more information, check out the Property Owner’s Guide to a Healthy Watershed. The Clean Lakes Alliance and the Friends of Lake Wingra are also good resources for learning about stormwater and how to protect local watersheds.
—Michael Hansen, land care manager