Laserfiche WebLink
2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br /> <br /> <br />Chapter 4: Hazard Identification and Risk Assessment 123 <br />4.6.5. Flood <br />4.6.5.1. Description <br />Floods are the most common and widespread of all weather-related natural disasters and result in more <br />deaths each year than tornadoes, hurricanes, and lightning. A flood is defined as an overflowing of water <br />onto dry land which occurs when the existing channel of a stream, river, canyon, or other watercourses <br />cannot contain excess runoff from rainfall or snowmelt. Table 4-63 lists and describes the different types <br />of flood. Flooding can be damaging, and it can happen with only a few inches of water or cover ing a <br />house up to the rooftop. Additionally, floods can occur within a few minutes or over a long period of time, <br />and last days, weeks, or longer.146F <br />146 <br />Table 4-63. Flood Types147F <br />147 <br />Type Description <br />River Flood <br />Occurs when water levels rise over the top of riverbanks due to excessive rain from <br />tropical systems making landfall, persistent thunderstorms over the same area for <br />extended periods of time, combined rainfall and snowmelt, or an ice jam. <br />Inland Flooding <br />Occurs when moderate precipitation accumulates over several days, intense <br />precipitation falls over a short period, or a river overflow because of an ice or debris jam <br />or dam or levee failure. <br />Flash Flood <br />Occurs during heavy or excessive rainfall in a short period of time, generally less than <br />six (6) hours. Flash floods are usually characterized by raging torrents after heavy rains <br />that rip through riverbeds, urban streets, or mountain canyons. They can occur within <br />minutes or a few hours of excessive rainfall. They can also occur even if no rain has <br />fallen, for instance after a levee or dam has failed, or after a sudden release of water by <br />a debris or ice jam. <br />Coastal Floods <br />Caused by higher than average high tide and worsened by heavy rainfall and onshore <br />winds (i.e., wind blowing landward from the ocean); the inundation of land areas along <br />the coast. <br />Storm Surge <br />An abnormal rise in water level in coastal areas, over and above the regular astronomical <br />tide, caused by forces generated from a severe storm's wind, waves, and low <br />atmospheric pressure. <br />Floodplains <br />Floodplain is synonymous with the 100-year floodplain and means that the land area is susceptible to <br />inundation with a 1% chance of being equaled or exceeded in any given year. The limit of this area shall <br />be based upon flood ordinance regulation maps or a reasonable method which meets the objectives of <br />the act.148F <br />148 <br /> <br />Floodplains are a part of a system that has evolved to accommodate changing water levels during the <br />course of each year. In a natural landscape, floodplains temporarily store floodwater during spring runoff, <br />reducing flood levels and slowing the river's flow. Those functions of floodplains can be impaired when a <br />river is restricted by riprap or a bulkhead, or when the floodplain's natural characteristics are changed by <br />development or by removal of native vegetation. <br /> <br />146 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Flood Basics. Retrieved from <br />https://www.nssl.noaa.gov/education/svrwx101/floods/. <br />147 NOAA, National Severe Storms Laboratory. (n.d.). Severe Weather 101: Floods. Retrieved from <br />https://www.nssl.noaa.gov/education/svrwx101/floods/types/. <br />148 Kittitas County. (2016). Shoreline Master Program. Retrieved from <br />https://www.co.kittitas.wa.us/uploads/documents/cds/smp/20160307-Kittitas-County-Shoreline-Master- <br />Program.pdf.