Cities are struggling to prevent flooding

Urban areas are more prone to flooding than other sites because streets, parking lots, and buildings are impermeable, meaning that water cannot enter the ground like in a forest or meadow. Instead, it flows.

Detroit, like many old cities, deals with rainwater runoff by combining it with sewage treatment plants. This mixture is pumped to the treatment plants. Last season, electrical outages and mechanical problems caused 12 four-pumps to be pumped at two major pump stations.

The agency has spent $ 10 million renovating these two pump stations in recent years and another hundreds of millions on other improvement work. To completely modernize the sewer system, a stormwater network would have to be built at a cost of more than $ 17 billion.

Stormwater infrastructure across the country is aging and many governments have turned to Band-Aid solutions instead of building more resilient systems. Mikhail Chester, An infrastructure and policy researcher at Arizona State University. Chester added that mechanical and electrical systems will occasionally fail during major storms.

However, even if the pumping stations had worked perfectly, they might not have prevented disastrous flooding.

Outdated models

Detroit’s pumping stations, like many stormwater infrastructures, were designed to withstand a 10-year storm, which means the amount of rainfall per hour, roughly the chance of a 10-year storm occurring in 10 years. A 10-year storm around Detroit would be about 1.7 inches of rainfall in an hour, according to data from the National Weather Service.

During the June storm, in some parts of Detroit there were intense levels of rainfall that would have been characteristic of a 1,000-year storm (3.7 inches of rain within an hour), much higher than the capacity of pumping stations, according to the water authority.

However, rain forecasts are based on historical data that do not indicate the true probability of major storms. Anne Jefferson, A hydrologist at Kent State University. Storms that are thought to be one in 10 in a given year are likely to occur more frequently now as a result of climate change. And he says few agencies are taking climate change into account when designing infrastructure.

“We’re locked into an atmosphere of the past,” Jefferson says.

Governments that hope to take climate change into account when designing infrastructure have uncertainty. Should they plan for the best or worst case emissions? It is difficult to predict how the predictions will affect precipitation.

Organizing larger storms is a wonderful goal, but it is also costly. Larger pumps and pipes are more expensive and more difficult to install, Chester says. And price increases are not linear, he adds: a double-capacity pump or pipe will in most cases be more than double the price.

Fast forward

Coastal cities face even more severe climate threats, and some are making aggressive investments to prevent them. Florida, Tampa, has spent $ 27 million renovating pump stations and other infrastructure after major floods in 2015 and 2016, Tampa Bay Times. They seem to be working on some new versions; this year, at least, the city avoided flooding in major storms like Hurricane Elsa.

However, when the sea rises on the coast of Tampa the pumps may soon cover the outlets. If the sea level reaches the point where the water comes out of the storm pipes, the system will not be able to remove the water from the city.

Some cities want to install other features, such as storm wells and gardens, to help manage urban flooding. Grasslands like rain gardens can reduce the volume and speed of excess water, Jefferson says. If enough of these facilities are built in the right places, they can help prevent smaller floods, he added, but like other stormwater infrastructure, they are usually not designed to stop flooding in larger storms.