The storm system along East Valley Road from SW 34th Street to the outfall at Panther Creek at SW 23rd Street might need to be replaced — but if and when it’s needed will be determined after a feasibility study.
Joe Farah, the city’s surface water engineering manager, said they’re not 100% sure that Renton will need to upsize and replace the existing storm system along East Valley Road. Farah said some minor ponding was observed during periods of heavy rain in December 2023, but compared to other projects, this is minor.
“So based on the precipitation and the capacity of the pipe and the elevation in the receiving waters, that would be Panther Creek and Springbrook Creek, we can tell from the model if we have possible capacity issues, and capacity issue meaning that the pipe is not big enough to convey all that volume of water from rain that will be flowing through that pipe,” Farah said. “So we thought we had a problem based on that model from 2007, and we’ve monitored it over 15 years.”
Farah said that in 2007, during the Eastside Green River Watershed plan, this site was flagged as a possible area for drainage problems, but since then, they haven’t noticed any issues until December 2023.
Farah said because the Washington State Department of Transportation will be doing construction work in that same area before 2030 to construct a culvert for fish to swim through to reach Rolling Hills Creek, city officials thought this would be a good time to see if the storm system along East Valley Road needs to be upsized and replaced.
“One of our questions that we are asking ourselves is, is it worth it? Because there’s a big opportunity since we’re disrupting the street, and they’re getting that culvert replaced,” Farah said. “If there was a time for us to improve our storm system on East Valley Road, this would be it, which is why we’re putting our eggs into this basket right now and trying to assess and decide what is the best thing to do right now.”
Although capacity issues could be a reason for replacing this storm system, Farah said there could be other reasons. Farah said the storm system pipe is very old, probably 50 years old, and they don’t know its condition.
Because they’ve noticed ponding, Farah said this feasibility study is a good opportunity to see whether it’s cracked, settling, or the joints are holding. If that’s the case, then a replacement at the same time that WSDOT is doing its work would be convenient, Farah said.
This feasibility study is funded by WSDOT’s surface water fees, which they pay Renton. Farah said the study looks at its necessity and benefits because the replacement project will need to be paid for by Renton ratepayers. If it is found to be necessary, then funding will need to be allocated for this project, which would be allocated from ratepayers. Because this has been on Renton’s capital plan for the last 16 years, he wants to fully flush out project investigation before executing it.
Farah said this feasibility study will also determine whether the culprit of this newfound ponding could be a beaver dam that has developed over the last three years. Farah said the study could also show whether the city needs to do some beaver maintenance instead of replacing the storm system to fix the ponding.
Farah said Panther Creek has a beaver dam, which elevates the water level. Farah said when Panther Creek elevates, it means the storm system on East Valley Road that is supposed to discharge the water would have higher water surface elevations in the drains on the street that collect the water and in the pipe, which makes ponding more severe.
“We can speculate and can say we are confident that if that beaver dam did not exist, then the ponding would be even less severe, possibly nonexistent,” Farah said. “So, there’s that issue, And, you know, it was also a lot of rain over multiple days. Remember, in December 2023, we had sustained rain over a three-week period. When you have sustained rain over a three-week period … beaver dam or no beaver dam, water in the creek is going to be high.”
