- Defining Hazards & Risks
- Types of Hazards
- Flooding
- Lake Levels
- Storms
- Erosion
- Other Hazards
Great Lakes communities experience a wide range of natural hazards that include flooding from upland runoff, high and low lake levels, severe storms, storm waves and storm surge, shoreline erosion, ice heaves, landslides, and rare, large edge waves (seiches) usually associated with low-pressure systems or cold fronts. All of these coastal hazards threaten lives and property, a problem that is becoming more critical as coastal development pressures increase and potential impacts of climate change manifest themselves.
Defining Hazards & Risks
What kinds of impacts are you seeing from current hazards like flooding, winter storms, erosion, or stormwater runoff? Combined sewer overflows, complaints about basement flooding, water infrastructure damaged, homes unlivable because of bluff failure? How are you addressing these threats? Are your current plans, policies, and projects accounting for hazards in a changing climate?
A natural hazard is a process that occurs under certain extreme environmental conditions in the atmosphere, on the earth’s surface, or underground. There are many different types of natural hazards, such as tornadoes, blizzards, drought, wildfire, volcanoes and earthquakes. Coastal hazards are those natural hazards that occur at the interface between the lake and the shoreline, inclusive of the uplands that impact the lake throughout the coastal watershed.
Coastal hazards refer to the risks of life and property on the coastline that are created by coastal flooding, high winds and waves, short- and long-term shoreline erosion, and storm surges. The risk that a natural hazard poses is considered by estimating the impact that it would have on the people, services, facilities, and structures in a coastal community. Risk is typically defined as “probability of an event x consequence” and the greater the frequency and/or impacts, the greater the risk.
"Risk can be thought of as the product of the frequency that a significant change will occur multiplied by impacts. Changes are often referred to as hazards or threats, and impacts as consequences. Both elements must be present for there to be a risk. If a change (flood) occurs there is no risk unless the change (flooding) causes an impact to something of value (e.g. recharging aquifers, damaging homes…). These impacts can be beneficial or adverse. Possible adverse changes are commonly referred to as hazards. Similarly risks are most often used to describe the possibility of a hazard causing adverse impacts. Opportunities, and not risks, are often defined when referring to positive impacts result from change." (Freitag et al., 2009)
Types of Hazards
Flooding
Flooding may result from a coastal storm, dam break, or a heavy rainfall within the coastal watershed. Development continues to intensify within flood-prone and marginal areas along the coast or in coastal watersheds. Protecting floodplains preserves the natural functions of ecosystems and also helps prevent loss of life and property from damaging floods.
Lake Levels
Low water levels present a hazard to navigation and water supply intakes, and limit riparian landowners’ access to the lake. High lake levels cause widespread flooding and bluff erosion. During these high water periods, storm surge and storm waves can cause severe property damage and shoreline erosion. Areas on the Great Lakes that experience chronic flood and erosion damages were typically constructed during times of low lake levels. (OMNR 2001).
Storms
The main threats associated with these hazards are storm surge, high winds, heavy rain and flooding, as well as tornadoes. Winter storms can produce rough lake conditions, coastal flooding, and beach erosion. Strong winter storms are also responsible for significant land losses around the Great Lakes.
Erosion
Coastal erosion is a process whereby large storms, flooding, strong wave action and human activities – such as inappropriate land use, alterations, and shore protection structures – wear away beaches and bluffs during a flood or storm or over a period of years. Erosion undermines and often destroys homes, businesses, and public infrastructure and can have long-term economic and social consequences.
Other Hazards
Potential water contamination from surface runoff is a major factor throughout coastal watersheds in the Great Lakes. Surface runoff provides a pathway for a wide variety of substances to enter the lakes from farm fields, such as nutrients and pesticides, and from urban areas and city streets including substances such as salt, sand, asbestos, lead, oils and greases. Surface runoff also includes a large number of materials deposited with precipitation, which may include particulates, bacteria, nutrients and toxic substances.
Finally, ice shoves (or scour) occur when ice is shoved up the shore away from the lake by water currents or wind. Damage can result if the moving ice contacts banks, bluffs and structures. Nearshore ice displaces wave energy lakeward, protecting the beach from wave-induced erosion, yet it may also contribute to erosion as the ice loosens sediment.
Image Gallery Photo Credit: 1. Michigan Sea Grant, 2. Jerry Holt – Minnesota Star Tribune, 3. Carole Y. Swinehart - Michigan Sea Grant Extension, 4. Minnesota Sea Grant & NOAA GLERL, 5. Minnesota Sea Grant & NOAA GLERL, 6. Tom Archer - Michigan Sea Grant, 7. Tom Archer - Michigan Sea Grant, 8. Michigan Sea Grant.
