hazard identification and vulnerability analysis - Mason County

Hazard Identification and Vulnerability Assessment
Much of the recent development in the County has occurred either in or near
flood plains. This development increases the likelihood of flood damages in two
ways. First, new developments near a flood plain add structures and people in
flood areas. Secondly, new construction alters surface water flows by diverting
water to new courses or increases the amount of water that runs off impermeable
pavement and roof surfaces. This second effect diverts waters to places that
were previously safe from flooding.
In years past, people living on or near rivers have taken it upon themselves to
remove gravel deposits thus helping to maintain river and stream channels. As
greater emphasis has been placed on maintaining salmon spawning areas, this
type of activity is now restricted and requires hydraulic permits for any activity in
the riverbeds. As a result, deposits of gravel have built up over the years, and
the river channels have become increasingly shallow, exacerbating the chances
of flooding. Low dikes constructed along the Skokomish failed in the December
2007 winter storm.
Mason County will always be vulnerable to flooding, especially in Skokomish
Valley, Tahuya River Valley and along the Satsop River.
Conclusions
Mitigation involves flood plain planning, buyout of flood prone residences,
elevation of homes and management coordinated by local, state and federal
agencies. Building codes and regulations applied to structures aid in mitigation.
Residents should have access to information on flood insurance. Where building
has already occurred on flood plains, emergency preparedness in the form of
sandbags, building materials, 3-day evacuation kits and alternate shelter should
be part of each resident's preparation for possible flooding.
Resources
Federal Emergency Management Agency
National Weather Service
United States Army Corps of Engineers, Northwest Division
Washington State Emergency Management Division
Western Regional Climate Center
Attachments
Skokomish River Basin Map
Tahuya River Basin Map
Satsop River Basin Map
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