Carson River Flood Event Planning Project East Fork Fire Protection District Carson River Flood Event Planning Project Executive Summary
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East Fork Fire Protection District Serving as Douglas County Emergency Management Under an Inter-local Contract Carson River Flood Event Planning Project East Fork Fire Protection District Carson River Flood Event Planning Project Executive Summary Prepared by Tod F. Carlini, District Fire Chief The East Fork Fire Protection District is charged with the responsibilities of Emergency Management for Douglas County, Nevada under an inter-local agreement between the Fire Protection District and Douglas County. While there are many uncertainties regarding the potential of flooding along the Carson River in Douglas County and an El Nino driven weather situation which could produce abnormal potential for that flooding, including alluvial, riverine, and debris type flooding, the East Fork Fire Protection District has taken a lead role in the development of flood orientated contingency and response planning. Douglas County has experienced all three types of flood events. Some with devastating results, such as was the case with the 1997 flood event. Most recently, the Johnson and Stephanie Lane community areas were heavily impacted with alluvial flooding following heavy rainfall in the Pine Nut Mountain Range, while the Fish Springs area actually saw debris/mudflow flooding in July of 2014. Debris from the 24,000 acre Bison Fire of 2013 contributed to this type of event. While not to deminimize the effects of flash flooding on the citizens and properties impacted by alluvial flooding, the attached work product and information gathering will focus primarily on the potential for riverine flooding, specifically along the East and West Forks of the Carson River as it flows through the Carson Valley. Consideration must also be made for a debris/mud flow type event due to the impacts of the 2015 Washington Fire in Alpine County. The information contained herein has been prepared from an emergency management perspective and represents the first phase of a two phase effort. As we attempted to design a functional Flood Response Guide, one of the first steps to assess the condition of the Carson River and evaluate conditions and hazardous, which under a flood situations, would either need to be addressed or at a minimum be identified as a concern. In meeting that objective our desire was to collect information from a core group of individuals, all with interests in the Carson River. Solicitations were made regarding concerns, problematic features, known weaknesses, and possible solutions more from a “practical” point of view, rather than from any type of specific engineering perspective. While Carson Valley Flood Event Planning Project 1 environmental considerations are an absolute necessity when addressing any issues along a navigable water course, such as the Carson River, the primary focus was in terms of what potentially could be done as emergency measures and/or assess flood potential necessary for the development of a separate Flood Emergency Guide Manual. The 1997 Flood resulted in one fatality, forced the closure of much business, flooded over 50 homes throughout the valley, forced the evacuation of 140 citizens, isolated many of the valleys communities, destroyed millions of dollars of public infrastructure, and resulted in a total loss of $55,000,000. Several years of drought have left the Carson River chocked with new growth vegetation, sand and gravel islands and other deposits, and an overall loss of river channel capacity. The flood of 1997 saw flows of 23,000 CFS, which is 4 feet above flood stage. The information contained within this document and the recommendations made, are the by-product of conversations and discussions with what should be considered one of Carson Valley’s most important resources, that being its agricultural community and the interest and history that it represents. This work would not have been possible without collaborating with members from the agricultural community, the Washoe Tribe of Nevada and California, and other interests along the Carson River and Carson Valley. The primary objectives for the Fire Protection District are actually quite clear and will serve as a basis for the development of the Flood Response Guide which is a separate document, however, understanding these objectives as part of this project is important: They include: 9 Reduce the loss of life and property of residents and visitors due to flooding through response coordination and mitigation actions 9 Ensure the safety of all responders and participants in the response 9 Support the residents, visitors, and businesses in prepare for, responding to and recovering from flooding 9 Provide an efficient, comprehensive organizational structure for emergency response and recovery 9 Coordinate ALL emergency operations within the county either with or without an official declaration 9 Coordinate the use of available resources, be they public or private, including, local, state, and federal 9 Recover from flood emergencies by providing for rapid and orderly damage assessment and providing necessary assistance to the highest degree 9 Establish a tiered activation of response levels following a deliberate and reliable situational awareness and input data from credible sources Carson Valley Flood Event Planning Project 2 9 Apply institutional knowledge, historical recollection, and recognize the roll that the agricultural community can plan in flood management in the Carson Valley Secondary and complimentary to the development of a Flood Response Guide, this is also an attempt to document notes, comments, historical perspective, and to define and prioritize potential emergency project work along the Carson River. While the scope and responsibility of that work is vested with others, and strictly from an Emergency Management standpoint, this work may serve as a starting point for Carson Valley Conservation District, engineering disciplines, environmental specialist, and regulatory agencies in the future. The executive management of the East Fork Fire Protection District would like to thank those members of the Carson Valley agricultural community and representatives from the Washoe Tribe of Nevada and California who participated in this endeavor. Basic History The Carson River is a northwestern Nevada river that empties into the Carson Sink, an endorheic basin. The main stem of the river is 131 miles (211 km) long although addition of the East Fork makes the total length 205 miles traversing five counties: Alpine County in California and Douglas, Storey, Lyon, and Churchill Counties in Nevada, as well as the Consolidated Municipality of Carson City, Nevada. The river is named for Kit Carson, who guided John C. Frémont's expedition westward up the Carson Valley and across Carson Pass in winter, 1844. The 205 mile Carson River watershed encompasses 3,966 square miles and includes two major forks in the Sierra Nevada in its upper watershed region. The 74-mile-long East Fork rises on the north slopes of Sonora Peak (just north of Sonora Pass at about 10,400 feet in southern Alpine County, southeast of Markleeville in the Carson-Iceberg Wilderness. The 40-mile-long West Fork rises in the Sierras near Carson Pass and Lost Lakes at 9,000 feet elevation and flows northeast into Nevada, joining the East Fork about 1 mile southeast of Genoa. The Carson River then flows north 18 miles to the end of the upper watershed at Mexican Dam just southeast of Carson City. In the middle watershed the river runs generally northeast from Carson City across Lyon County, past Dayton. The middle watershed ends in eastern Churchill County at the Lahontan Dam. Here river flows are augmented by water from the Truckee River and stored in the Lake Lahontan reservoir. Downstream from the dam (in the lower watershed) much of the water is used for irrigation in the vicinity of Fallon, with limited flows continuing northeast into the Carson Sink. Clear Creek, which begins at about 8,780 feet on Snow Valley Peak (Toiyabe National Forest, Carson Range) west of Carson City, is the only perennial tributary of the Carson River main stem, and is protected by the Nature Conservancy. Carson Valley Flood Event Planning Project 3 Flood Types There are actually three types of flooding that can impact Douglas County. They include main stem riverine flooding, alluvial fan flooding, and debris flow/mud flow flooding. Douglas County most recently experienced alluvial fan flooding and debris flow/mudflow flooding on the eastern side of the Carson Valley and in Southern Douglas County. Main Stem Flooding Flooding of the main channel of a river involves flows that overbank and flood adjacent areas known as floodplains. A floodplain is generally described as a strip of relatively smooth land bordering a river that overflows at time of high water. Specific geomorphic features define a floodplain. For example, the Carson Valley is broad and flat due to the uplift and subsequent erosion of the Sierra Nevada, Carson, and Pine Nut Ranges as well as deposition of sediment carried by the Carson River at flood stage. Likewise, the Carson River channel looks more like a creek bed rather than a deep incised channel found in larger rivers across the Nation. Because the source of most of the stream flow originates from the mountain snowpack, the Carson River has not needed to incise its channel to accommodate snowmelt runoff but simply uses the floodplain as a discharge surface. Alluvial Fan Flooding Alluvial-fan flooding occurs on alluvial-fan surfaces adjacent to the mountain block which are gently sloping; fan-shaped landforms created over time by deposition of eroded sediment, and are common at the base of mountain ranges in arid and semiarid regions such as much of the western United States (National Research Council, 1996). Flooding on alluvial fans is characterized by high-velocity flows, active processes of erosion, sediment transport and deposition, and unpredictable flow paths. This type of flooding is the result of intense cloudbursts from summer convective storms — common in Nevada.