City of Renton officials have emergency plans in place to protect south Renton in the event of severe flooding of the Green River due to damage at Howard Hanson Dam in the Cascades.

The Green River runs through Auburn and Kent – the Green River Valley – and skirts the industrial area of south Renton before jogging through Tukwila.

After last January’s floods, the U.S. Army Corps of Engineers, which operates the dam, discovered depressions in land adjacent to the dam and temporarily restricted its water-holding capacity.

As a result, the Green River Valley could be more vulnerable to flooding, according to the corps.

“Our biggest concern is that we have a significant number of businesses that are affected,” said Preeti Shridhar, a spokeswoman for the City of Renton. In Auburn and Kent, homes, as well as businesses, are at risk of severe flooding.

The city has e-mailed businesses in the potentially affected areas, informing them of the situation, according to Shridhar. The city has suggested the businesses purchase flood insurance and look to the city’s Emergency Management Department as a resource, she said.

Renton is also working with other cities to address the regional impacts of flooding, she said. That cooperation includes making plans for what roads or highways to use in case an evacuation is needed. The city has specific routes in mind, but which ones are used would depend on different flood scenarios, Shridhar said.

The cities would potentially have hours to plan for the proper contingency, she said, based on early warning and the time it would take for a flood crest to reach the lower reaches of the river.

The City of Renton also is looking at purchasing and deploying an emergency notification system – a reverse 911 – that would enable the city to send notification via e-mail to those affected in such a disaster.

City of Renton officials are planning on visiting the dam later this week.

The King County Flood Control District Board met with the U.S. Army Corps of Engineers and emergency response representatives Monday to receive a status update on the Howard Hanson Dam.

Since 1961, the Howard Hanson Dam has been providing flood risk reduction on the Green River. Prior to the construction of the dam, the floodwaters of the Green River would spread out almost unimpeded across the valley. Because major flooding has been reduced, the Green River Valley is now home to tens of thousands of residents, major employers and the region’s largest warehouse and distribution operations.

The daily economic loss from a devastating flood could reach about $46 million, according to a King County press release.

Corps Seattle District Commander Col. Anthony Wright briefed the Flood District Board on the status of tests on the right abutment depressions and the timeline for repairs.

According to the press release, the Corps has high confidence in the structural integrity of the Howard Hanson Dam, and that the dam presents no immediate danger to people and property below the dam. Engineers are currently evaluating the depressions at the dam and more data will be collected this spring to enable engineers to determine if the pool elevation can be raised higher without additional impacts to the abutment or more importantly the dam structure itself.

“We appreciate the Corps’ timely sharing of information,” said Flood District Board Supervisor Julia Patterson, in the press release. “Our priority is to ensure effective plans are in place to protect people and property before the next flood season. This information is critical in helping local jurisdictions, residents and businesses prepare in case there is a significant flood event.”