USGS “Coastal Squeeze” Will Threaten I-5 Along Nisqually River Delta

The current design of I-5 restricts critical ecological functions impacting salmon survival, is at a high risk of being overtopped by a major flooding event and has limited capacity to handle the growing South Sound economy and population – a key component to national security since 30% of the JBLM workforce live south of the Nisqually River. The Legislature allocated $75 million in the Move Ahead WA package; SSMCP requests phasing of these funds to allow timely delivery of the project. $19 million toward the roundabouts on SR  507 is needed in 2023 and $56 million for the Nisqually River Delta will be needed when NEPA is complete. If additional funding is available, SSMCP supports prioritizing projects along the Mounts Road to Tumwater corridor, including hard shoulder running between Sleater Kinney Rd and Henderson Blvd.  

SSMCP believes investing in the I-5 Nisqually corridor should be a legislative priority.  Preliminary findings of the USGS hydrologic study find that I-5 will be over topped by Nisqually River flooding. USGS lead scientist, Eric Grossman stated, “it is not if, but when”. The combination of global warming leading to sea level rise, channel reorientation, more prolific rain events, and snow melt will result in the 100-year flood occurring 4-5 times more frequently than historic norms (22-23 year event).  The science tells us that in as little as 17 years flooding events will become much more frequent in the Nisqually delta with the ox bow on the Nisqually River reaching the highway. This would result in more frequent events like the 1996 Chehalis flood but on the Nisqually delta.

SSMCP believes that in order to improve the region’s transportation system performance and protect environmentally sensitive areas, as an initial step, ask $7.5M be allocated toward development of an alternative I-5 highway design. SSMCP asks the Legislature to invest along the Nisqually River Delta to restore impaired ecosystems, mitigate the flood risk to I-5 and increase highway capacity through the corridor.