After frequent flooding and two road closures, the intersection of SW 43rd Street and Lind Avenue SW near Ikea is slated to receive storm system upgrades.

Renton will soon begin the design process, which includes a feasibility study to see how they can divert some of the stormwater at the intersection, according to Joe Farah, the city’s surface water engineering manager. Farah said that giving the water at the intersection more places to go — as opposed to just the one outfall that it is currently routed to — will free up the pipe and help prevent flooding.

Farah said the intersection has been flooding for multiple years now, which affects Renton and a few Kent businesses near the Lind Avenue SW and 180th Street intersection in Kent. Farah said the intersection had to be closed for a little over two days on two different occasions because flooding: once in December 2019 and once in March 2022.

Farah said that when that intersection closes, an emergency response is created, and personnel must always be there waiting to reopen the road as soon as feasible. Farah said another negative of the flooding at that intersection is private property flooding. Farah said surrounding establishments are affected by flooding in their parking lots.

Farah said the goal is to implement a solution to solve the drainage problem, have the least environmental impact, and last a long time. The ideal solution, Farah said, is to leverage the existing outfalls in the valley, which feed into Springbrook Creek.

“I’m going to give you an analogy of roads because it really helps the people imagine how it kind of works the same way for stormwater. So we need to provide relief for a congested highway. You could either build an entirely new highway that has six lanes that would replace the existing highway that is made up of four lanes,” Farah said. “Or you could create a fork off of that highway. So, if I forked the highway to a different path, I have now two paths that people could take. They could take I-5 or I-405, and eventually they get to the same place.”

In the case of the stormwater system, Farah said instead of adding a new outfall to Springbrook Creek, which could impact the environment and be costlier, they could split the water currently going to only one outfall so it instead goes to two or more already existing outfalls. Farah said rerouting the stormwater rather than constructing a new outfall would be cost-effective and quicker to deliver.

Farah said if they need to create a new outfall, rather than reroute water to existing outfalls, this could add another two years to the project timeline because they will need to take extra time for environmental mitigation, which requires additional time for permitting and instituting. For example, he said if they added a new outfall, they would need to add nets so fish don’t get confused by a new pipe and try to enter it, or they might need to figure out what kind of restoration they will need to do if they have to remove some of the riparian areas for a pipe.

Options

Farah said they’re going to figure out if they can use two existing outfalls, but if they can only utilize one, they will go with Option 1, which is to reroute water to Southwest 39th Street and resize the pipe from about 30 inches to 60 inches. Farah said Option 2 is to utilize the stormwater outfall on nearby Southwest 39th Street and the outfall on Southwest 34th Street.

Farah said if the flooding at the SW 43rd Street and Lind Avenue SW intersection is not fixed, it could worsen with climate change, so when designing these upgrades, they account for this possibility.

“Climate change could cause more intense rainfall over a short duration because as air warms up, warmer air can hold more moisture. You get more intense rainfall, similar to how rains in the tropical regions, because the warmth there, you get thunderstorm style rain,” Farah said. “Where in colder climates, like us up here in Seattle, we don’t get, like, heavy thunderstorm-style rains that cause a burst of rain over a short period of time. We get sustained lower intensity rainfall over a longer duration.”

Farah said people should care about this project because if there is less flooding at the SW 43rd Street and Lind Avenue SW intersection, traveling will be safer, and there is less likelihood of closures, which could affect commutes. Farah said many people utilize that road to get to Ikea or Costco, and he believes people would feel more comfortable and happier driving in the winter knowing that there’s reduced risk of flooding along that corridor.

Regarding funding, Farah said the project is partially funded by a $250,000 grant from the King County Flood Control District, with additional funding from the City of Renton. He said the estimated construction cost is around $3 million, though the numbers are not set in stone, and they will be looking to get more grants to fund the project.