Detroit airport drainage system overwhelmed by intense rain

Torrents of rain water closed a key artery into Detroit Metro Airport on Thursday and delayed or canceled a slew of flights following a storm, a situation that left many people stranded, confused and frustrated amid flooding throughout the region.

Airports are supposed to be ready for such events — in fact, the Wayne County Airport Authority says the stormwater system at Detroit's regional airport, "has the capacity to detain more stormwater than at any other North American airport."

So what caused the flooding that prevented access to McNamara Terminal? Airport media officials did not immediately respond to requests for comment. But a meteorologist and a state official said it was likely just too much rain in a short amount of time.

Wait, it rains all the time. How was this different?

The airport recorded a little more than 3 inches of rain over the course of a few hours Wednesday leading into Thursday, said Andrew Arnold, a meteorologist with the National Weather Service in Detroit.

However, there were reports of as much as 7 inches of rainfall recorded in the same period in areas near the airport, he said.

That official total at the airport doesn't set any new records — airport officials determined more than 4.5 inches of rain fell during the mass Detroit flooding on Aug. 11, 2014, which also prompted flight delays — but it's absolutely in the top 10 to 15 worst rainfalls in the area.

"A lot of it all fell at once, or in a very short period of time, which can be very hard for spots, especially in urban areas, to handle that much water," Arnold said.

The airport can't handle that amount of rain?

According to the airport's website, DTW's drainage system can hold about 515 million gallons of water, roughly the same amount in 750 Olympic-size pools. That comes after investing more than $175 million into the airport's draining and deicing management systems since 1990.

Translated to rain runoff, the system, "can contain a 4.5 inch runoff event," according to the airport's website.

That's substantially less than the amount of rain reported in areas near the airport.

In addition to simple rainfall totals, plenty of different communities drain to similar areas, noted Diane Cross, a spokeswoman for the Michigan Department of Transportation who lives near the airport.

Key portions of Interstate 275 around the airport also flooded, and remained impassable as of Thursday afternoon. That's due to some of the same factors, Cross said — the interstate is low-lying, with water running to a draining area that is already overflowing.

"Water is flowing down, back into the area where we're pumping water out of," Cross said.

More: Roads to DTW's McNamara Terminal reopen; Canton under water after flooding

More: Weather forecast for Southeast Michigan calls for more severe showers, flooding

Both northbound and southbound lanes on I-275 near the airport will remain closed through at least Thursday evening, and possibly into Friday, as more severe weather is expected.

Cross said no system is prepared to immediately handle that much rain in such a short amount of time

"Mother Nature could have given us the standard amount of rain over a longer time period, or a less amount of quantity in that same time period, but there's nothing that we could have done differently for this," Cross said Thursday afternoon.

"This has happened. It has happened in other areas, and it will happen again."

How did the airport and officials respond to the rain?

At approximately 8 a.m., the airport announced flooding completely blocked tunnels leading to McNamara Terminal. By noon, water started to recede from the area and a little after 3 p.m. the airport announced regular access to the terminal, used by Delta and several other major airline carriers.

The Federal Aviation Administration "slowed traffic" to and from the airport Thursday due to flooding, said an agency spokesperson. That prompted delays, both in departures and arrivals.

Arnold noted that there could be additional storms coming through the area Thursday evening that could exacerbate flooding in metro Detroit. The FAA spokesperson said the agency will adjust the flow of air traffic into the airport to account for changing conditions.

Contact Dave Boucher: dboucher@freepress.com.

This article originally appeared on Detroit Free Press: Detroit airport drainage system overwhelmed by intense rain