In May of 2022, the Rum River reached its highest peak flow since 2001 following torrential rain events in Isanti and Mille Lacs Counties. The roadway to the boat ramp in Rum River Central Regional Park in Anoka County was inundated under feet of water. When the floodwaters receded, 90 linear feet of bank had completely washed out, threatening the roadway and boat ramp, and leaving and exposed eroding bank dumping sediment into the river. This section of washed out riverbank was stabilized using a Flexamat PLUS articulated concrete mat at the toe, and a regraded and native-seeded slope above. A rock barb installed at the downstream end will provide in-channel habitat for fish and invertebrates while also kicking flow out away from the boat ramp.
The Flexamat articulated concrete was chosen for this project because an immediately adjacent project installed in 2015 is still holding very successfully, even after the flooding. An advantage of Flexamat vs. rock is that the Flexamat has void spaces that allow vegetation to grow between the blocks, masking the concrete during low water conditions, and providing additional habitat benefit. Traditional riprap does not allow this vegetation growth, and can look like a rock wall during low water.
In the spring, we will add bare root seedlings of shoreland tree and shrub species to the project site. The native grasses and sedges seeded into the bank will begin to grow, and the whole bank will establish deep-rooted native vegetation which will keep the soil anchored for years to come. A video short of this project can be found on ACD's YouTube page: https://www.youtube.com/shorts/eUHBV5TSNi8. To see other streambank stabilization projects installed throughout Anoka County, please see the virtual project tour on ACD's website.