The First Storm
Construction at
Mary Beth Doyle Park is nearly complete. To the left is a recent aerial
photo showing the basic layout. (Click for close up.) At the
bottom of the photo, you can see that there is still a pond, though
it's a little smaller than the old one. This new pond can be drained
down so equipment can enter to remove sediment from time to time.
This planned maintenance element will dramatically improve water
treatment.
The pond now flows to the wetland area in the upper half of the photo. When it rains, the small channel you see will expand and fill the much of the basin. More on that later.
Between the pond and wetland, you can make out a pedestrian bridge. This bridge is part of the new walking loop. The old asphalt walkway has been replaced, and a new gravel path goes between the pond and wetland all the way to the parking lot at the end of Birch Hollow. The loop is a little over one-half mile.
This week, the parking lot will be paved. Many trees and shrubs are already in place and the native plants are being installed. The basin will also be seeded with a native plant mix after the first of October. That seed will lay dormant over winter and germinate next spring. The park will remain closed until the vegetation is established. A ribbon-cutting ceremony and celebration of the park’s namesake, Mary Beth Doyle, is being planned for spring.
On August 19th and 20th, 2.3 inches of rain fell in the Ann Arbor area.
While the wetland
has already treated several smaller storms, this was the first event that
filled the basin completely - nearly 50 acre feet. When that happens, water
begins to flow over the embankment dam seen to the right. On a
dry day, that dam is 4.5’ above the creek. Once the dam is overtopped, there
is no more capacity for pollutant removal, but flood protection continues as
designed. Depending on weather patterns, this will occur several times each
year. Within 2-3 days, the water will drop down again to its normal
level.
One of the benefits of holding that much water back is that the downstream stretch of Malletts Creek to the Huron River will not rise and fall so quickly when it rains. The stream banks should become more stable, erosion and scouring should decrease and habitat should improve. There are many more things we can do to protect Malletts Creek and other urban waterways, but this facility is a big step forward.
