Minor failure underscores major improvement in Spokane’s stormwater system

A failure earlier this month in one of the largest parts of Spokane’s stormwater system initially set off some alarm bells, but city officials argue it highlights the major work done in the last year to keep pollution out of the Spokane River.

“If this had happened even a year ago, it all would have ended up in the river,” said Kirstin Davis, spokeswoman for the city’s Public Works agency. “It’s a setback, for sure, but it could have been much worse.”

Persistent rainfall earlier this month led to larger-than-expected stormwater flows through the Cochran Basin, the city’s largest stormwater collection area at over 5,000 acres, and the focus of an over $25 million project meant to protect the river. A newly built link in the chain of that stormwater system failed on Nov. 13, as heavy stormwater discharged into a catchment in Downriver Park and burst through an earthen wall.

“We tried to shut off that pipe, but the pressure was too much,” Davis said. “We could slow it down, but couldn’t stop it or do anything else until it stopped raining.”

As of Saturday, the Spokane area had already seen one of the top 20 rainiest Novembers on record, according to the National Weather Service. The last time the region saw as much rain in November was in 2006.

Builders expected the catchment to overflow during heavy rains, but water was supposed to pour over the top of a rock wall and down the hill to swales below that would capture the extra water before it ran into the river. Instead, the flow of water became significant enough that the stormwater cut through the earthen embankment in two places, causing a minor landslide that undercut the catch’s concrete pad.

Some amount of polluted stormwater and sediment from the landslide swept into the river after the initial breach, though the water eventually naturally cut a channel flowing directly into the swales. A fabric fence also prevented a significant amount of the sediment from going into the river, nearly burying it, and a second fabric fence has been installed.

The public only became aware of the breach after the Spokane Riverkeeper, a nonprofit tasked with monitoring river conditions and fish populations, highlighted the failure on social media on Friday after it found continued runoff into the river.

“We are saddened and disappointed to see this project struggle with the current rainfall, as this new infrastructure should be capable of withstanding storms of this size,” the organization wrote on Facebook.

It’s not clear how much water or sediment made it into the river, Davis said, though the city believes most of the water settled into the swales downhill. She acknowledged that the design of the earthen wall was potentially flawed and would be re-examined before the structure is repaired, though she warned repairs weren’t likely until after winter.

Stormwater discharge can have a serious impact on the health of the river, often carrying chemicals from roads and pipes that, if left unfiltered, can harm fish. This was the case in western Spokane, where the city found low oxygen levels in water downriver of the TJ Meenach Bridge. Near the Downriver Golf Course, the city began work in 2019 on a series of projects to properly treat stormwater before it enters the river.

That stormwater system is also supposed to have better fail-safes to handle unusually large stormwater flows. However, a pump that would have allowed crews to divert water elsewhere, such as towards the Downriver Disc Golf Course filtration ponds, was not fully installed prior to this late-autumn downpour, Davis said.

While the failure of recently built infrastructure is a setback, the fail-safes that mitigated the damage highlight the effectiveness of the overall system, said Katelyn Scott, who works as Spokane Riverkeeper’s water protector.

“Even though this collapse happened, we can still see that the swales and bio-infiltration ponds below helped capture that water,” Scott said. “Even with this small setback, the setback shows us that the rest of the project is working really well, and we’re hopeful and confident that it will be a great benefit in the long run.”

Major, expensive infrastructure upgrades in recent years are also a marked improvement over the city’s more than 100-year history of simply dumping its stormwater and, often, its raw sewage into the river. These efforts – the last of which was finished in 2020 – included more than a dozen tanks capable of holding more than a million gallons of sewer and stormwater runoff that had previously flowed freely into the river.

“Before these systems were in place, we saw significant discharges even on dry days,” Scott said.

Those systems can still fail, and last year over 10,000 gallons of combined sewer and stormwater was discharged into the river, but the tanks have prevented millions of additional gallons from being added.

There has been no recorded overflow from this system so far this year.