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Cities are fighting to prevent flooding

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Urban centers are more prone to flooding than other areas because roads, parking lots and buildings are impermeable, meaning that water cannot infiltrate into the ground like a forest or a meadow. Instead, scroll down.

Detroit, like many older cities, deals with storm water that flows by combining it with drains. This mixture is then pumped into treatment plants. During the recent storm, electrical outages and mechanical problems have shut down four of the 12 pumps at two major pump stations.

The agency has spent $ 10 million in recent years to upgrade just these two pump stations, and hundreds of millions more for other improvements. But a complete modernization of the sewer system would require the construction of a separate rainwater network at a cost of more than $ 17 billion.

Rainwater infrastructure around the country is aging, and many governments have resorted to Band-Aid solutions instead of building more resilient systems, he says. Mikhail Chester, an infrastructure and policy researcher at Arizona State University. And mechanical and electrical systems are forced to fail occasionally during major storms, Chester adds.

However, even if the pump stations had worked perfectly, they could not prevent disastrous flooding.

Obsolete models

Detroit’s pumping stations, similar to many rainwater infrastructures, are designed to keep pace with a 10-year storm, meaning an amount of precipitation in an hour that has about a 10 percent chance of happening. in a given year. A 10-year storm in the Detroit area will rise to about 1.7 inches of precipitation in an hour, according to data from the National Weather Service.

During the June storm, part of Detroit saw intense levels of precipitation that will be more characteristic of a 1,000-year storm (over 3.7 inches of rain in an hour), far beyond the capacity of the weather stations. pumping, according to the authority of the water.

But precipitation forecasts are based on historical data that may not represent the true probabilities of major storms, according to Anne Jefferson, hydrologist at Kent State University. Storms that presumably have a 10 percent chance of happening in a given year are probably happening more often now because of climate change. And he says few agencies take climate change into account in their infrastructure designs.

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“We live in a past climate,” Jefferson says.

Governments hoping to take climate change into account when designing infrastructure face uncertainty – should they plan for the best case scenario or worst case scenario? And how exactly emissions will affect precipitation is difficult to predict.

Planning for larger storms is an admirable goal, but it is also costly. Larger pumps and pipes are more expensive to build and harder to install, says Chester. And price increases are not linear, add-ons — a pump or pipe with double the capacity will be more than double the price in most cases.

Fast forward

Coastal cities are facing more severe climate threats, and some are investing aggressively to ward them off. Tampa, Florida, spent $ 27 million to upgrade pump stations and other infrastructure after major flooding in 2015 and 2016, according to the Tampa Bay Times. Some of the improvements seem to be working – at least this year, the city has avoided flooding during major storms such as Hurricane Elsa.

However, rising sea levels along the Tampa coast may soon cover pump outlets. If the sea level reaches the place where the water is supposed to come out of the storm pipes, the system will not be able to draw water from the city.

Some cities are trying to install other features, such as storm ponds and rain gardens, to help manage urban flooding. Grasslands such as rain gardens can reduce the volume and speed of excess water, Jefferson says. If enough of these plants are built in the right places, they can help prevent smaller floods, he adds, but like other rainwater infrastructure, they are usually not designed to stop flooding during longer storms. great.


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