DEVELOPING A LEGALLY DEFENSIBLE SETBACK ORDINANCE ALONG PART OF THE LAKE SUPERIOR SHORELINE

The shoreline of Bayfield County, Wisconsin, varies from beach and dune to bluffs over 150 feet (50m) high. Although some of the bluffs are armored by bedrock at the base, some consist almost entirely of clayey till. Past shoreline recession rates range to over 2 feet (0.6 m) per year. Because of its proximity to the Minneapolis-St. Paul population center, there is increasing development of the shoreline. At present the only requirement is a setback of 75 feet (23 m) from the edge of the bluff for new construction. An ordinance being presented to the Bayfield County Board, uses geologic information to establish a more reasonable setback distance for bluff shorelines. The geology of the bluff has been described in two studies and we use that vertical distribution of sediment as the basis for interpretation. Stable slope angles for each material were established by measuring natural slopes and determining what angle appears to separate stable from unstable slopes. In addition, a variety of laboratory tests were conducted. Recession rate was determined in a previous study by comparison of orthophotos taken at least two different times in the past. The formula being proposed to the County Board is Total Setback Distance (from bluff top) = (annual recession rate (feet/year)*50)+(setback distance necessary to establish a stable slope angle)+(facility setback of 75 feet). The most difficult component to determine is the stable slope angle component of set back because it requires knowledge of the present angle, and this varies considerably over short distances. Future LIDAR may make it possible to determine slope angle at the scale necessary for the calculation, but at this time estimates are posted on a website and county staff will measure the slope angle at the time application is made for a building permit.