Flood Series: Causes, disaster prevention topics at initial meeting
HOUGHTON — As high rain or flood events become more prevalent, many areas are putting a renewed focus on natural methods to mitigate flooding.
Michigan Technological University researchers spoke to a standing-room-only crowd at the Carnegie Museum Thursday on the changing climate patterns and extreme weather conditions which contributed to the severity of the June 17 flood.
They also spoke about flood-control measures such as wetlands or retention ponds that can trap water and delay flow.
As air gets warmer, it holds more water vapor, said David Watkins, a Tech civil and environmental engineering professor. At the same time, accelerated warming in the Arctic has shifted the jet stream that circulates air globally, turning it from a direct path to a “lazy river,” Watkins said.
On the weekend of the flood, a low-pressure trough pulled humid air from the Gulf of Mexico.
“We had as much water vapor in the atmosphere above us as places in Louisiana and Alabama,” he said. “That’s why it felt like Louisiana and Alabama that day.”
That morning, it collided with a cold-air mass; they locked horns over the area and stayed that way for several hours.
In the wettest parts of the Keweenaw, more than 6 inches fell in six hours.
Runoff is exacerbated by concrete cover. Any rainfall will run off a paved area, while the ground in a residential yard will absorb half of it. In a wooded area, the level of runoff drops to 2 inches.
With less runoff absorbed by the ground, peak discharge is higher and comes sooner. The watersheds that saw the most flooding in June were those where water circulated through the watershed the fastest, such as Ripley Creek, which cleared in three hours.
Those prone to flooding in the spring, such as Sturgeon River or Trap Rock, have slower circulation times and actually saw less flooding.
By 2030, extreme weather events will be more likely, and urbanization will have accelerated, said Alex Mayer, professor of geological and mining engineering sciences and civil and environmental engineering at Tech. In 2030, a projected 60 percent of all urban areas will have been built in the past 30 years.
Whereas “gray infrastructure” is designed to clear stormwater from the environment as quickly as possible, green spaces can serve the functions of natural forests and wetlands, such as collecting water and filtering pollutants.
Numerous people have asked Mayer what impact the removal of wetland areas by Huron Creek over the past few decades contributed to the storm.
“This is an unusual storm,” he said. “I suspect even if the wetlands had been intact, it would have been difficult for those wetlands to take up the storage.”
For smaller storms, wetlands and other green spaces can have an impact. Rain gardens can store water and allow the groundwater to recharge. In one photo shown by Mayer, an outlet allows it to collect runoff from the surrounding pavement.
Swales — shallow, sloped depressions — catch water, slow its path and help it infiltrate the ground. Parking lots at the beaches in Hancock and Lake Linden have them, Mayer said.
Homeowners or administrators can be behind the adoption, Mayer said. Means can include ordinances and watershed districts. Rebates and tax credits can also encourage properties to add the features.
The talk is the first in a series of Father’s Day Flood presentations held by the Keweenaw Land Trust and Carnegie Museum.
The talks, part of the Carnegie’s Keweenaw Natural History Seminar Series, will look at causes and effects of the flood, as well as responses.
The next meeting will be on Dec. 4, when Tech’s Veronica Webster will talk about the intensity of recent rainfall events and if it represents “the new normal.”