City of Sammamish - COVID-19 (Coronavirus) Information & Resources
Thank you for your patience as the City recovers from the recent flooding and the ensuing state of emergency declared for King County. Our stormwater team has compiled some frequently asked questions and their answers regarding the current closure of Issaquah-Fall City Road.
The road is still flooded. Why isn’t the water going down faster?
The City sees water over the shoulder of the road at this area along Issaquah Fall City Road (IFCR) and old IFCR, to the north and west of Endeavor Elementary School almost every year. Typically, that amount of water does not affect traffic. This is the first time in the City’s knowledge that the entire road has standing water over it and is deep enough to require us to close the road for safety reasons.
This area is the lowest spot topographically; stormwater runoff from all directions flows to this low spot naturally and collects here. This is what engineers call a “closed depression” or “closed contour”, meaning the water does not have a natural creek or stream outlet. Instead, the water has to infiltrate into the sandy soils underlying the area. Stormwater runoff resulting from “normal” rainfall amounts are typically able to completely infiltrate quickly enough such that flooding does not occur here.
The Puget Sound experienced a record-tying number of rainy days in the month of January. This rain saturated the soils. On top of that, Sammamish and the region experienced the largest rain event in the past decade between February 5th and 7th, recording almost 5-inches of rain. All of the rain within this particular watershed flowed to this point, filled up the wetland, and flooded the road (IFCR and Old IFCR).
City crews have been measuring the water twice a day since the road closed on February 7th. Water levels are lowering about an inch to two inches per day. As of February 12th, there is still about 8 inches of water covering the centerline of the road.
What is the City doing to fix this? Can you pump the water somewhere?
The City has been measuring the infiltration rate, seeing if the water will recede naturally. However, because of slow infiltration, the large volume of water waiting to infiltrate, and more rain on the horizon, the City planning to pump the water from the road into the stormwater ponds at Endeavor Elementary School. The City has coordinated with the school to allow this pumping. We were not able to do so prior to today because the pond next to the road was full of water.
A few years ago, we experienced a sustained heavy rainfall (not as large as the one last week) causing the water to encroach into the westbound travel lane causing traffic to swerve into the eastbound lane. We were successfully able to lower the water level by pumping into the school’s stormwater ponds so we are hopeful it will work again, despite the fact that there is far more standing water than we have ever seen before.
What is the permanent fix so this doesn’t keep happening?
Ultimately this drainage issue will be corrected when the City constructs the IFCR Phase 2 project, which is currently in the design and will most likely raise the road in this section when it is constructed. However, it is still several years out from construction.
Until the IFCR Phase 2 project is built, the City will continue to closely monitor this area during the rainy season and take appropriate action depending on the situation. We will continue to use every avenue possible to keep the community and stakeholders notified including Police, Fire and affected school districts via the City’s webpage, social media and emails. To sign up for alerts, please go to https://service.govdelivery.com/accounts/WASAMMAM/subscriber/new
How long will the road remain flooded/closed?
We are working on getting the pump and hose and plan to start pumping today, February 12th. We hope to be able to pump the water down sufficiently to open up one lane of traffic as soon as possible.
How often are we going to see flooding events like this?
We can’t predict how often events like this will happen in the future. Climate change is affecting the weather of the Pacific Northwest. Rather than light rain drizzling over long periods, we are receiving more “Pineapple Express” events, which bring warm, moisture-laden air from the equator to the Pacific Northwest, which result in heavy rain events over short periods of time.
Suffice to say, this may not be the last time we see heavy rains resulting in flooding.
Thank you for your patience!
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