Blog

Urban centers are more susceptible to flooding than other areas because streets, parking lots and buildings are impenetrable, which means that water cannot penetrate the ground like in a forest or meadow. Instead, it flows.

Detroit, like many old cities, handles running storm water by combining it with wastewater. Then this mixture is pumped to the treatment plant. During a recent storm, power outages and mechanical failures caused four of the 12 pumps at the two main pumping stations to fail.

The agency has spent $ 10 million over the past few years upgrading these two pumping stations alone, and hundreds of millions of dollars on other improvements. But a complete renovation of the sewerage system will require the construction of a separate stormwater network at a cost of more than $ 17 billion.

Stormwater infrastructure across the country is aging, and many governments are turning to Band-Aid solutions instead of building more resilient systems, says Michael Chester, an infrastructure and policy researcher at Arizona State University. Chester adds that mechanical and electrical systems sometimes fail during severe storms.

However, even if the pumping stations worked flawlessly, they could not have prevented a catastrophic flood.

Obsolete models

Detroit’s pumping stations, like many other stormwater infrastructure, have been designed to withstand a 10-year storm, that is, rainfall in an hour that has about a one in 10 chance of falling in any year. The 10-year storm in the Detroit area will generate about 1.7 inches of rain per hour, according to the National Weather Service.

During the June storm, parts of Detroit experienced intense rainfall that would have been more characteristic of a 1,000-year storm (more than 3.7 inches of rain per hour), far exceeding the capacity of the pumping stations, according to water authorities.

But rainfall forecasts are based on historical data that may not reflect the true likelihood of severe storms, according to Ann Jefferson, a hydrologist at Kent State University. Storms, which supposedly have a one in 10 chance in any given year, are now likely to happen more often due to climate change. And she says few agencies take climate change into account when designing their infrastructure.

“We are locked in the atmosphere of the past,” says Jefferson.

Governments hoping to incorporate climate change into their infrastructure design face the uncertainty of whether they should plan for a best or worst emission scenario? How exactly emissions will affect precipitation is difficult to predict.

Planning for stronger storms is a great goal, but it is also expensive. Large pumps and pipes are more expensive to build and more difficult to install, Chester said. And the price increases are not linear, he adds: a pump or pipe with twice the capacity will, in most cases, more than double the price.

Flash forward

Coastal cities face even more serious climate threats, and some are actively investing in preventing them. According to the Tampa Bay Times, Tampa, Florida spent $ 27 million to upgrade pumping stations and other infrastructure after major floods in 2015 and 2016. Some of the updates seem to be working – at least this year the city has escaped flooding during severe storms like Hurricane Elsa.

However, rising sea levels along the Tampa coastline could soon close pump outlets. If the sea level reaches the point where water is supposed to come out of storm pipes, the system will not be able to remove water from the city.

Some cities are looking to install other features, such as storm ponds and rain gardens, to help cope with urban flooding. Lawns such as rain gardens can reduce the volume and rate of excess water, Jefferson said. She adds that if enough of these facilities are built in the right places, they can help prevent small floods, but like other storm water infrastructure, they are usually not designed to prevent flooding during severe storms.