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CHAPTER 11. FLOOD <br />11-17 <br />• Interstate 90 <br />• State Route 10 <br />• State Route 970 <br />• U.S. Route 97 <br />Some of these roads are built above the flood level, and others function as levees to prevent flooding. Still, <br />in severe flood events these roads can be blocked or damaged, preventing access to some areas. <br />Bridges <br />Flooding events can significantly impact road bridges. These are important because often they provide the <br />only ingress and egress to some neighborhoods. <br />Water and Sewer Infrastructure <br />Water and sewer systems can be affected by flooding. Floodwaters can back up drainage systems, causing <br />localized flooding. Culverts can be blocked by debris from flood events, also causing localized urban <br />flooding. Floodwaters can get into drinking water supplies, causing contamination. Sewer systems can be <br />backed up, causing wastewater to spill into homes, neighborhoods, rivers and streams. <br />Levees <br />Levees have historically been used to control flooding in potions of Kittitas County. According to County <br />GIS records, there are approximately 17 miles of earthen levees in the county. There are also levees on <br />many smaller rivers, streams and creeks that protect small areas of land. Many of the levees are older and <br />were built under earlier flood management goals. Many of these older levees are exposed to scouring an d <br />failure due to old age and construction methods. <br />11.5.4 Environment <br />Flooding is a natural event, and floodplains provide many natural and beneficial functions. Nonetheless, <br />with human development factored in, flooding can impact the environment in negative ways . Migrating <br />fish can wash into roads or over dikes into flooded fields, with no possibility of escape. Pollution from <br />roads, such as oil, and hazardous materials can wash into rivers and streams. During floods, these can settle <br />onto normally dry soils, polluting them for agricultural uses. Human development such as bridge abutments <br />and levees, and logjams from timber harvesting can increase stream bank erosion, causing rivers and <br />streams to migrate into non-natural courses. <br />11.6. VULNERABILITY <br />Many of the areas exposed to flooding may not experience serious flooding or flood damage. This section <br />describes vulnerabilities in terms of population, property, infrastructure and environment. <br />11.6.1 Population <br />A geographic analysis of demographics, using the Hazus model and data from the U.S. Census Bureau, <br />identified populations vulnerable to the flood hazards. The information was pulled from census blocks that <br />intersected the floodplain as follows: <br />• Economically Disadvantaged Populations—Approximately 6 percent of the people within <br />the 100-year or 500-year floodplain are economically disadvantaged, defined as having <br />household incomes of $10,000 or less. <br />• Population Below Poverty Level— Approximately 17 percent of the people within the 100- <br />year or 500-year floodplain live below the poverty line, defined as having household incomes <br />of $30,000 or less.