2019_KittitasCountyHMP_Volume 1_For Adoption

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CHAPTER 11. FLOOD 11-12 and property. Another element that characterizes a community’s flood threat is the length of time floodwaters remain above flood stage. The Kittitas County flood threat system consists of a network of precipitation gages throughout the watershed and stream gages at strategic locations on the Yakima River that constantly monitor and report stream levels. This information is fed into a USGS forecasting program, which assesses the flood threat based on the amount of flow in the stream (measured in cubic feet per second). In addition to this program, data and flood warning information is provided by the National Weather Service. All of this information is analyzed to evaluate the flood threat and possible evacuation needs. Due to the sequential pattern of meteorological conditions needed to cause serious flooding, it is unusual for a flood to occur without warning. Warning times for slow-rise floods can be between 24 and 48 hours. Flash flooding can be less predictable, but potential hazard areas can be warned in advanced of potential flash flooding danger. 11.3. SECONDARY HAZARDS The most problematic secondary hazard for flooding is bank erosion, which in some cases can be more harmful than actual flooding. This is especially true in the upper courses of rivers with steep gradients, where floodwaters may pass quickly and without much damage, but scour the banks, moving the edge of the floodplain closer to buildings or causing them to fall in. Flooding is also responsible for hazards such as landslides when high flows over-saturate soils on steep slopes, causing them to fail. Hazardous materials spills are also a secondary hazard of flooding if storage tanks rupture and spill into streams, rivers or storm sewers. There are various public health concerns that arise as a result of exposure to flooded areas, including drowning, infectious diseases from contaminated floodwaters, exposure to chemical hazards, electrical hazards from downed power lines, and injury from objects carried by flood waters (CDC, 2017). Mold growth is a common occurrence in flood-damaged homes and damp environments. Mold can also spread if it is disturbed during the clean-up process, as it is transferred from one surface to another. Infants, children, immune-compromised patients, pregnant women, individuals with existing respiratory conditions (allergies, multiple chemical sensitivity, and asthma) and the elderly appear to be at higher risks for adverse health effects from mold. Symptoms include nose and throat irritation, wheezing, coughing, asthma attacks in individuals who have asthma, and lower respiratory tract infections (in children). People with pre - existing respiratory conditions also may be susceptible to more serious lung infections (FEMA 2010). 11.4. CLIMATE CHANGE IMPACTS Use of historical hydrologic data has long been the standard of practice for designing and operating water supply and flood protection projects. For example historical data are used for flood forecasting models and to forecast snowmelt runoff for water supply. This method of forecasting assumes that the climate of the future will be similar to that of the period of historical record. However, the hydrologic record cannot be used to predict changes in frequency and severity of extreme climate events such as floods. Going forward, model calibration or statistical relation development must happen more frequently, new forecast-based tools must be developed, and a standard of practice that explicitly considers climate change must be adopted. Climate change is already impacting water resources, and resource managers have observed the following: • Historical hydrologic patterns can no longer be solely relied upon to forecast the water future. • Precipitation and runoff patterns are changing, increasing the uncertainty for water supply and quality, flood management and ecosystem functions.