Urban centers are more prone to flooding than other areas because streets, parking lots and buildings are impermeable, meaning water cannot leak into the ground the way it would in a forest or lawn. Instead, it flows.
Detroit, like many older cities, deals with rainwater by combining it with sewage. This mixture is then pumped to treatment plants. During a recent storm, electrical outages and mechanical problems knocked out four of the 12 pumps at the two main pumping stations.
The agency has spent $ 10 million over the past few years on upgrading just these two pumping stations and hundreds of millions more on other improvements. But a complete modernization of the sewer system would require the construction of a separate stormwater network at a cost of over $ 17 billion.
The country’s rainwater infrastructure is aging, and many governments have resorted to Band-Aid solutions instead of building more resilient systems, he says. Michael Chester, an infrastructure and policy researcher at the University of Arizona. And mechanical and electrical systems will occasionally fail during major storms, Chester adds.
However, even if the pumping stations worked perfectly, they might not have prevented the catastrophic floods.
Detroit’s pumping stations, much like the multitude of rainwater infrastructure, are designed to track a ten-year storm, meaning the amount of rain within an hour that has roughly one in ten chances of happening any year. A ten-year storm in the Detroit area would amount to about 1.7 inches of rain per hour, according to the National Weather Service.
During the June storm, heavy rainfall was recorded in parts of Detroit that would be more characteristic of a 1,000-year storm (over 3.7 inches of rain within an hour), far above the capacity of the pumping stations, according to authorities.
But rain predictions are based on historical data that may not represent the real prospects for major storms Anne Jefferson, a hydrologist from Kent State University. Storms that are assumed to occur in one in ten in any year are likely to occur more frequently now due to climate change. And he says few agencies take climate change into account in their infrastructure projects.
“We lock ourselves into the past climate,” Jefferson says.
Governments hoping to take climate change into account when designing infrastructure face uncertainty – should they plan a best or worst-case emission scenario? And how exactly the emissions will affect the rains is hard to predict.
Planning for major storms is a wonderful goal, but it is also expensive. Larger pumps and pipes are more expensive to build and harder to install, Chester says. And price increases are not linear, he adds – a pump or pipe of double capacity will in most cases be more than twice the price.
Coastal cities face even more serious climate threats, and some are investing aggressively to prevent them. Tampa in Florida spent $ 27 million on upgrading pumping stations and other infrastructure after the major floods of 2015 and 2016, according to Tampa Bay Times. Some upgrades seem to be working – at least this year, the city has avoided flooding during major storms like Hurricane Elsa.
However, rising seas off the coast of Tampa may soon cover pump outlets. If the sea level reaches the point where water should come out of storm pipes, the system will not be able to remove water from the city.
Some cities want to install other features, such as storm lakes and rain gardens, to help manage city floods. Grass areas like rain gardens can reduce the amount and speed of excess water, Jefferson says. If enough of these facilities are built in the right places, they can help prevent minor floods, she adds, but like other rainwater infrastructure, they are not usually designed to stop floods during major storms.