Agenda - Planning Commission - 02/02/2017

Home

Actively eroding and/or failing bluffs have also been identified as problems by citizens and government officials in the Lilydale, Mendota, and Mendota Heights area. Heavy rains over the past decade - including those in June 2014 - led to significant erosion and the failure of some bluffs within the MRCCA, including failures off Highway 13 in Mendota Heights (see Figure 3) and below Fairview University Hospital in Minneapolis. With FEMA funding, the DNR conducted an investigation' of these and other bluff failures associated with the June 2014 rain events in the Mississippi and Minnesota River valleys'. The structural geologist conducting this evaluation found that all failed bluffs within the MRCCA had slopes had been modified for building foundations, stormwater management facilities, or road construction, and that these modifications contributed to bluff failure. In these particular instances the bluff failures also resulted in significant damages to built infrastructure. Figure 3. Highway 13, Great Rivers Trail failure in Mendota Heights. Photo from http://www.myfoxtwincities.com/ story/25740202/mudslide-closes-highway-13-in-mendota. Bluffs also need protection because they provide wildlife habitat and support native plant communities. As illustrated by Minnesota's Land Cover Classifications System (MLCCS), a GIS-based classification system, there is a greater occurrence of native flora and fauna along bluffs and steep slopes'° Better corridor -wide management practices addressing structure placement and vegetation, land alteration, and stormwater management can reduce the risk of soil erosion and bluff failure as well as economic loss and human injury. Current Regulatory Status Executive Order 79-19 does provide special protection of "bluffs with a slope greater than 18 percent," but does not define the term "bluff." Executive Order 79-19 does, however, define a bluffline as "a line delineating the top of a slope connecting the points at which the slope becomes less than 18 percent" and establishes a 40 foot structure setback from the bluffline. Executive Order 79-19 also limits certain vegetation and land alteration activities within the bluffline setback and prohibits new structures on slopes 18 percent or greater. An examination of local ordinances within the MRCCA indicates that currently bluff definitions and standards vary widely across communities, as does administration of those requirements in local zoning ordinances. Many communities simply define a bluff as any slope greater than 18 percent, while others define them as slopes ranging from 12 percent to 40 percent. Some communities have specified the spatial extent of bluffs through use of minimum horizontal and/or vertical distances over which the 8 Jennings, C. 2015. http://www.dnr.state.mn.us/mlccs/index.html 10 http://www.dnr.state.mn.us/mlccs/index.html 23