Record high Great Lakes levels increase flooding risk along shoreline communities

By Scott Robertson, Senior Water Resources Engineer, Grand River Conservation Authority
Published with permission from the Grand River Conservation Authority

The Great Lakes drainage basin covers an area of approximately 766,000 km2, with the freshwater volume stored within the lakes typically quoted as representing about 18 per cent of the world supply and 84 per cent of North America’s supply. Water levels in the Great Lakes are affected by many natural factors, the primary ones being precipitation, evaporation, runoff, groundwater, ice, aquatic growth, meteorological disturbances and tides. A very small measure of human control exists throughout the Great Lakes system through various locks, canals, and dams, with operational considerations involving aspects such as mitigation of flooding, marine transportation and hydroelectric power generation. None of these controls has more than a negligible impact on Lake Erie water levels.

To some extent, lake levels are somewhat predictable and fluctuate on a range of time scales, from multi-year and seasonal at a lake-wide scale, down to hours, minutes, and even seconds at a local scale. A summary of current basin-wide conditions includes:

  • Lake Superior exceeded its seasonal record levels for May and remained above record for 4 months, before dipping to just below record to start September.
  • The Lake Huron-Michigan system, which effectively “shares” a water level, approached record levels in early summer, but has since receded slightly, entering September only 8 cm below its record for the date, as set in 1986.
  • Lake Erie surpassed both seasonal and historically-recorded levels, previously set in the mid-1980s and late 1990s, in early May. Levels have remained well above both seasonal and historically-recorded highs through the entirety of the summer to the present. As of September 19, they remained 8 cm above the previous record-high for the date, set in 1986, but are slowly declining.
  • On the heels of record-breaking flood levels in 2017, Lake Ontario exceeded even those heights in early June and remained at record-breaking levels through the first week of August.
  • More information about the Great Lakes, characteristics and conditions is available on the Fisheries and Oceans Canada website at https://waterlevels.gc.ca.

Lake Erie Conditions

So, what does all this mean for Lake Erie and the Grand River shoreline communities of Dunnville and Port Maitland? High levels create conditions ripe for flooding and erosion, potentially altering the shoreline, damaging property or municipal infrastructure, and even potentially injury or loss of life.

While the record-high day-to-day levels resulted in some minor nuisance flooding in very low-lying areas at its peak in May and June, the more significant concern on Lake Erie relates to wind-driven storm surge weather events. Of all the Great Lakes, the shallow character of Erie leaves it particularly susceptible to such conditions.

Winds of sufficient speed and duration are able to “push” water from the west end of the lake to the east end, temporarily raising levels at Dunnville and Port Maitland by up to two metres for hours at a time, before relenting and allowing the water to slosh back to the west end of the lake, like in a bathtub. On top of these storm surges, isolated waves of up to another two metres could also occur, with increased likelihood during such wind events.

The lowest level of flooding starts to occur at Port Maitland at a lake elevation of approximately 175.5 m, with the highest instantaneous level ever recorded at 176.62 m (December 2, 1985). As of September 12, 2019, the stable lake level is 174.88 m, meaning that it would only require a relatively moderate storm surge wind event to initiate low-level flooding along some coastal areas. A significant event could result in near record or even record flooding.

On the plus side, levels are continuing to recede at approximately seasonal rate, but on the negative side, the types of weather events that create storm surges as described above occur primarily in the fall and winter seasons. There remains a lot of water flushing through the upper Great Lakes system draining into Lake Erie, which means that levels, through dropping nicely, will likely remain unseasonably high throughout this crucial period, resulting in a higher potential for lakeshore flooding and erosion along the Lake Erie shoreline. A Lake Erie Conditions Statement – High Lake Level Outlook has been in place since October 2018, and is expected to remain in place for the coming months.

Much will depend on how dry the next couple months are, how much the lake levels can continue to drop, and how kind Mother Nature decides to be with respect to westerly or south-westerly winds.

Find out how to prepare for floods via the Haldimand County Emergency Services and GRCA websites.

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