MSU Extension

As of the end of September, 2014, the water levels of all five Great Lakes were above their long-term averages according to the Great Lakes Water Level Dashboard. This is a notable milestone given the record lows of lakes like Michigan and Huron within the last couple of years (see Great Lakes water levels for the summer of 2014 - what’s up (or not)?). It is difficult to predict future water levels, but one thing is for certain – the Great Lakes are a dynamic system and levels will continue to fluctuate over time.

The National Climate Assessment predicts for the Midwest that “Extreme heat, heavy downpours, and flooding will affect infrastructure, health, agriculture, forestry, transportation, air and water quality, and more. Climate change will also exacerbate a range of risks to the Great Lakes.” One such risk on the Great Lakes is shoreline damage from large storms, which are predicted to increase in intensity. Besides erosion and impacts on water quality, large Great Lakes storms coupled with high water levels can damage municipal infrastructure and private property. One way to protect current and future property from damage and loss due to coastal hazards is to make sure coastal zoning standards are tailored appropriately to the shoreline characteristics of the area.

It may come as a surprise to some, but there is no statewide minimum building setback for the entirety of Michigan’s Great Lakes shoreline. Instead, building setbacks are determined almost on a property by property basis with both local government zoning and state regulated high risk erosion area (HREA) setbacks possibly applicable on a given property.

High risk erosion area (HREA) setbacks are regulated by the Michigan Department of Environmental Quality (DEQ). This setback varies from location to location based on coastal recession (erosion) data the DEQ collected years ago. Some local units of government adjacent to the Great Lakes have no HREAs and therefore have no state-regulated building setbacks from the water’s edge (but other coastal management regulations may still apply). For those local units of government with HREAs, there are two relevant setbacks for coastal construction – a 30-year and a 60-year setback. The 30-year setback applies to ‘readily-moveable’ structures and the 60-year setback applies to more permanent structures. The HREA setbacks are measured from the erosion hazard line, generally, a line of stable vegetation, or the landward edge of any slumps on the bluff in cases where the bluff is actively eroding. A DEQ/US Army Corps of Engineers joint permit is required prior to construction in a HREA.

Despite state regulation of HREAs along portions of the Great Lakes shoreline, local governments still have a stewardship role to play. Through adoption of zoning ordinances, local governments regulate placement of structures near the shoreline and other sensitive natural features. Typically along the Great Lakes shoreline, zoning ordinance setbacks are measured from the ordinary high water mark (although some communities choose to measure from the historically-high water level recorded in 1986). Local zoning setbacks along the Great Lakes vary, but generally fall within the range of 75 to 150 feet. If both zoning and HREA setbacks apply to a given property, both setbacks must be satisfied and permits are needed from both regulatory entities (the local government and the DEQ).

Whether in a HREA or not, local zoning setbacks from the Great Lakes OHWM may need to be adjusted, given higher water levels and threats posed by storms (indeed, the OHWM itself changes with changes in lake levels). This is because coastal damage is generally the result of a combination of storm surge and wave run-up. During a storm, strong, sustained winds blowing across a large extent of open water (i.e. a large fetch) push water causing it to pile up or ‘setup’ in the form of a storm surge along the leeward (downwind) side of the lake. Winds can also cause a seiche to form on the Great Lakes – a periodic oscillation of lake levels caused by a rapid change in wind direction or air pressure (see What’s up (or not) with Great Lakes water levels?), which can also result in temporarily higher water levels.

It’s no surprise that during a large storm waves crash higher up the shoreline than they do under more normal conditions. Referred to as wave run-up, the reach of waves is largely dependent on the wave height in deep water, the distance between waves (the wave period), the slope of the lake bottom at the site, and the slope of shoreline at the site. The Army Corps of Engineers calculates 50-year and 100-year waves at periodic locations along the entire Great Lakes shoreline as part of Wave Information Studies. A 50-year wave has a two percent chance of being equaled or exceeded in any single year and a 100-year wave has a one percent chance of being equaled or exceeded in any single year. Knowing the height of 50-year and 100-year waves along a local government’s Great Lakes shoreline is another valuable piece of information for calculating appropriate setbacks. Many locations along the Great Lakes have 50-year wave heights of seven feet or more.

The next article in this two-part series highlights additional coastal hazards, discusses the appropriateness of shoreline erosion control structures, and suggests how a local government might proceed with this information.