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2025 Hazard Mitigation Plan
<br />Kittitas County, Washington
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<br />Chapter 4: Hazard Identification and Risk Assessment 125
<br />There are many flood problem areas throughout Kittitas County; however, the principal flood sources are
<br />riverine flooding, urban flooding, and irrigation facilities.
<br />Riverine Flooding
<br />Large scale developments with urban densities adjacent to the Yakima and Teanaway rivers (i.e., Elk
<br />Meadows, Elk Meadows Park, Pine Glen, Sun Island, Sun Country, Teanaway Acres, and the Teanaway
<br />Wagon Wheel) have experienced substantial flood damage. The County also has numerous streams with
<br />large and unpredictable floodplains and flood capacities. These include, but are not limited to, Cabin,
<br />Cole, Big, Little, Silver, Gold, Manastash, Taneum, Wilson and Reecer creeks.
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<br />Floods on the Yakima, Teanaway, and Cle Elum rivers occur as the result of snowmelt in spring and early
<br />summer and occur after heavy rainfall in November and December. Ice and debris can have an impact
<br />on flood stages when culverts and bridges are obstructed. The spring/summer snowmelt floods are
<br />characterized by slow rise and long duration of high flow; river stages may be increased by ice and debris
<br />jams. The fall/winter flood crests are reduced because flood storage is available after the irrigation season
<br />in Kachess, Keechelus, and Cle Elum lakes. However, these reservoirs control only a small part of the
<br />runoff, and storage may not be available if two (2) winter flood events occur in short succession. The
<br />three (3) reservoirs have a combined storage capacity of 833,700 acre feet (157,800 acre feet in
<br />Keechelus Lake; 239,000 acre feet in Kachess Lake, and 436,900 acre feet in Cle Elum Lake). These
<br />reservoirs were constructed for irrigation purposes but are also operated for flood control on the basis of
<br />runoff forecasts.
<br />Urban Flooding
<br />Kittitas County has experienced rapid change due to urban development in rural areas where drainage
<br />systems are comprised of a series of pipes, roadside ditches, and channels. Urban flooding occurs when
<br />drainage systems lack the capacity to convey rainfall runoff to nearby creeks, streams, and rivers. When
<br />the drainage systems in place become overwhelmed, roads and transportation corridors become the
<br />conveyance.
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<br />The main contributors to urban flooding are rainfall intensity and duration; however, topography, soil
<br />conditions, urbanization and groundcover also play an important role. Urban floods can be a great
<br />disturbance to daily life as roads can become impassable, and people may be unable to go to work or
<br />school. Economic damage can be high, but casualties are usually limited because of the nature of the
<br />flooding.
<br />Irrigation Facilities
<br />The cities of Ellensburg and Kittitas are surrounded by complex irrigation systems consisting of the Kittitas
<br />Reclamation District North Branch Canal and Whipple Wasteway, and the Ellensburg Water Company
<br />and Cascade Irrigation District canals. These systems, which cover 330 miles, distribute water for
<br />irrigation and may at times provide incidental flood control. However, the system has a decreasing
<br />capacity downstream and can become overwhelmed when used to route floodwaters. Significant floods
<br />have occurred in the past when this system diverted floodwater from one basin to another. Additionally,
<br />potential irrigation district infrastructure failure could create a flood hazard.
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<br />The Flood Insurance Rate Maps (FIRMs) show the flood zones, floodplain boundaries, and Base Flood
<br />Elevation (BFE) and are used for floodplain management, flood insurance ratings, and to determine flood
<br />insurance requirements. These maps show areas with a 1% chance of flooding each year, commonly
<br />known as the 100-year floodplains, and are shown as the Special Flood Hazard Areas (SFHA) in the
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