A new floodplain map using the “best available science” shows the areas subject to flooding aren’t much different from the 2006 and 1982 maps.
However, it may change the projected depth of flooding.
While Chehalis uses a 2006 floodplain map, Centralia uses a 1982 map; no study was done for Centralia in 2006. Centralia Director of Community Development Emil Pierson said the new data doesn’t expand the floodplain, but he is concerned that it may change the depth.
Pierson said if the change in depth is significant, he is concerned about standards for building and development, especially for the Port of Centralia.
“If we adopt a higher standard base flood elevation, now they have to go to a different elevation … which means money,” he said.
The city is using the 1982 standards, but offers builders the standards based on the 2007 base flood elevation and they can decide if they want to build that high.
Pierson expects the new data will show depths closer to the 2007 flood. Whether to adopt a higher standard is a decision for the city council, he said.
However, if the Mellen Street to Blakeslee Junction project, including the dike, is worked into the model, then it should lower the depth.
Jim Kramer, of Kramer Consulting, hired to facilitate and oversee Flood Authority meetings and work, didn’t have depth numbers readily available at a Monday meeting with a committee including Lewis County, Chehalis and Centralia officials.
With little difference between the two floodplain maps, Chehalis City Manager Merlin MacReynold said that brings up the question, “Why change?” However, if there is a push for jurisdictions to adopt Karpack’s map, he doesn’t see Chehalis city officials or councilors having major concerns about making the switch. If the new floodplain map is adopted, it isn’t expected to affect building regulations in Chehalis.
The agency officials also learned that the Federal Emergency Management Agency is OK with them using the latest data for a floodplain map, the areas subject to flooding and previous data for floodway mapping, water channels and land areas for discharging flood water.
Larry Karpack, a principal hydrologist and hydraulic engineer with Watershed Science and Engineering, worked on updating the floodplain.
Information about the updated mapping will be shared with the Chehalis River Basin Flood Authority at its May 21 meeting.
