hazard identification and vulnerability analysis - Mason County

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Resources such as water and gas supplies. Plans should be realistically exercised at the County and City levels to insure workability and relevance to disaster response. United States Geological Survey University of Washington Geophysics Program Washington State Department of Natural Resources Washington State Department of Transportation 17
FLOODING Definition: An inundation of dry land with water. Flooding is the most common hazard occurring in Mason County. Heavy, prolonged rain in the fall, winter or spring months often results in saturated ground and high stream flows. Due to ground saturation, Mason County businesses and homes located in low-lying areas tend to flood during prolonged periods of rain. • River building floods: River building floods are caused by heavy, prolonged rain, melting snow, or both. Prolonged heavy rains and high freezing levels are the common cause for river flooding in Mason County. Runoff from the melting of low elevation snow often contributes to these floods. • Tidal floods: Tidal floods occur when high tides, strong winds, heavy swell, and low atmospheric pressure combine to produce flooding. • Flash floods: Flash floods are characterized by a very rapid quick rise of the water level in a small river, stream or dry wash. In the most extreme case, a flash flood is a literal wall of water moving down a steep canyon or ravine. The brief intense rainfall from a thunderstorm is usually the cause of a flash flood. The Skokomish River is considered to be a flash flood river. Tidal changes from Hood Canal combined with increased runoff from the Olympics have produced a history of frequent flooding. The Skokomish River has recently been identified as a “flash flood” river. History Mason County issued disaster or emergency declarations for flooding in 1964, 1974, 1975, 1979, 1990, 1994, 1995, 1996, 1997, 2003, 2006 and 2007. Historically, flooding occurs to some extent in Mason County every year. Hood Canal and Puget Sound beaches are often affected by flood tides compounded by heavy rainfall and high tides. 18
Page 1 and 2: MASON COUNTY HAZARD IDENTIFICATION
Page 3 and 4: Seattle, 20 miles northwest of Olym
Page 5 and 6: Mason County, due to its location a
Page 7 and 8: Resources United States Geological
Page 9 and 10: HISTORY VI. Felt by all; many frigh
Page 11 and 12: America, the Juan de Fuca plate sli
Page 13 and 14: Puget Sound basin would directly af
Page 15 and 16: Subduction Zone Earthquakes: Althou
Page 17: Conclusions Mason County will exper
Page 21 and 22: ATTACHMENT I SKOKOMISH RIVER BASIN
Page 23 and 24: ATTACHMENT III SATOP RIVER BASIN 22
Page 25 and 26: normal part of most forest and rang
Page 27 and 28: LAND SHIFT (SLIDES / EROSION) Defin
Page 29: HIGHWAY 101 MAJOR SLIDE AREAS (Sout
Page 38: SLIDE AREAS ALONG HIGHWAY 3 37
Page 43 and 44: HARSTEME ISLAND SLIDE AREAS 42
Page 45 and 46: SEVERE STORMS Definition Severe sto
Page 47 and 48: The most severe snowstorms that hav
Page 49 and 50: TSUNAMI, HIGH WAVES, SEICHES Defini
Page 51 and 52: VOLCANOS/ASH FALL Definition A volc
Page 53 and 54: • Magma or molten rock or lava or
Page 55 and 56: Conclusion volcano. Examples of suc
Page 57 and 58: its three 27,000 kilowatt generator
Page 59 and 60: Major petroleum shortages developed
Page 61: History Hazardous material incident

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