1.) Introduction

2.) Stable Angle

3.) Structure Life

4.) Local Regulations

Construction Setback

Building on the lakeshore must account for the effects of erosion on the bluffs. Bluffs are dynamic, and their retreat may be slowed, but never stopped. A well-constructed building might have a useful life of 70 to 100 years. A home built too close to the bluff may have to be moved to save the structure, or be demolished.

Setback refers to the total distance from a bluff a new building is required to be.

Different municipalities have different setback requirements. This calcuator demonstrates multiple scenarios on a fictional lakeshore, comparing three different methods for calculating setback:

  • Stable Slope Angle Distance
  • Structure Life
  • Local Regulation

Disclaimer: Results from this calculator should not form the basis for any decision making. Rather, this tool is intended to show general comparison between different calculation methods.

Stable Slope Angle

The first method of setback calculation is based on the height, angle, and material of the bluff, compared to its stable angle.

Stable bluff angles are the angle of slope in which a major slough or collapse is unable to occur. Along Lake Michigan, for example, bluffs generally have a stable angle of 22 degrees, but different bluff materials in different places result in different stable angles.

Bluff height can be categorized as high (over 70 feet) or low (under 70 feet). Bluff heights are difficult to calculate.

Setback is calculated from the bluff toe. Essentially, it is the difference two triangles. One triangle is based on the current height and current angle of the bluff, and the other triangle is based off the current height and stable angle of the bluff. The distance between the tops of these two triangles is the stable angle setback

Use the triangle tool below to experiment with different bluff parameters, when you're done, select calculate to see the setback line draw on the map.

Disclaimer: bluff heights vary greatly over distance, while this calculator assumes a single, constant height.

Structure Life

On the Wisconsin shore of Lake Michigan, bluffs erode, on average, 2-3 feet per year. This recession rate is far from constant. There could be many years of relative stability followed by a large destabalizing event.

When constructing a building near a bluff, it is important to consider how long you want the building to last. In some cases, the natural recession rate may be greater than the municipal setback requirements.

Select values below. When you're ready, select calculate to draw a new line on the map. How does this line compare with the stable angle setback line?




Local Regulations

While in some places construction setback is calculated based on the stable slope angle, in other places, setback is a flat value, such as 75 feet, calculated from the bluff crest. Other municipalities have may similar "flat values".

Hit calculate when you're ready. How does the resulting line, based on Mequon's municipal law, compare to the stable angle or natural recession rates?

Drag this line to adjust the size of the triangle.