The Chisago SWCD has been working intently on stabilizing the bluff that once was the bank of the glacial St. Croix River. With the water level much lower today, the old bank has become a steep hillside and has been subject to severe erosion as land use has changed over the past 150 years. The past five years have seen a special focus on the area, thanks in large part to a series of Clean Water Fund grants, funded through the Clean Water, Land and Legacy Amendment. In 2011, the Chisago SWCD completed an inventory of all actively eroding gullies along the escarpment from the south end of Wild River State Park to the Chisago/Washington County line. North of this area, the escarpment is less severe and, therefore, gully erosion is also less severe. The report identified hundreds of gullies, but prioritized the top 33 most actively and severely eroding for top prioritization.
In 2012 and again in 2014, the Chisago SWCD was able to secure Clean Water Fund grants to implement projects to stabilize the gullies identified in the inventory report. These are often large projects with large watersheds, requiring detailed engineering and planning. A common practice used is to “pool up” the water temporarily at the top of the watershed, before it reaches the head of the gully. A large berm, or mound, is built along the edge of the escarpment to hold water back during a rain event. A pipe inside the pooling area lets the water out slowly, at a velocity that will not cause erosion in the gully channel. By reducing the volume and velocity of water in the gully channel at one time, the channel is able to stabilize itself and erosion no longer occurs.
Between 2012 and 2015, about half of the identified projects have been completed. A total of 11 water and sediment control basins, 1 grade stabilization, 5 grassed waterways, 3 diversions, and a vegetated swale have been installed for a total reduction of 265 tons of sediment and 346 pounds of phosphorus reaching the St. Croix River. In 2016, the SWCD was awarded a Clean Water Fund grant to stabilize two more very large gullies in Taylors Falls. One of these gullies runs through a residential neighborhood and has been a problem for many years and the other gully is within Interstate State Park. Both projects are planned for 2016.
Between all 4 grants and match, the SWCD has leveraged over $777,000 for stabilizing the St. Croix River escarpment and protecting the water quality of the St. Croix River!
Photos: Left-edge of field erosion along the Escarpment; Right-in-field water and sediment control basin