Flood Reduction

PROPOSED COAL CREEK FLOOD REDUCTION PLAN

(Draft for review by CCWF Volunteers)
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At our community meeting on July 10, 2000, Steve Allen, PE with TVA discussed the flooding situation in Coal Creek. He informed us that Coal Creek is susceptible to intense flooding because of its geographic location (i.e. mountains located adjacent to flatter terrain) which causes storms to stall over the watershed. For example, 12 inches of rain fell on Redoak and Cross Mountains on July 24, 1965. Most of the runoff from the storm drained into the adjacent Stony Creek watershed. The resulting flood killed a family of five and literally destroyed the community of Clinchmore.

At a meeting on August 17, 2000, Dave Turner, Environmental Specialist with TDEC will explain the problems associated with dredging Coal Creek to reduce flooding. An ecosystem is destroyed and the dredging increases downstream flooding. A flood reduction plan involving dredging has winners and losers. Flood reduction plans in the 21^st Century need to provide win-win solutions.

After conversations with representatives from TVA, TDEC, NRCS, and Anderson County, the most attractive method to address the flooding problem appears to be the construction of a dry dam in the unpopulated, upper reaches of Coal Creek. Dry dams have a successful history as win-win flood management structures that protect the environment. The Miami Conservancy District in Ohio has been using these structures since the 1930s. TVA used dry dams to provide flood protection for Bristol. TVA considered the use of a dry dam to protect Coal Creek from flooding in the 1970s, but decided on a dredging plan because it was cheaper. Win-lose plans are often cheaper than win-win plans.

The proposed flood reduction plan for Coal Creek involves building an 80-foot high dam in Tennessee Hollow. During normal conditions, no pool is present upstream of the dry dam. Water would flow through a spillway pipe at the dry dam. Upstream and downstream of the dam, there would be no change to the stream. If trout spawning can eventually be achieved, then they could access upstream areas through the spillway pipe at creek level.

During flood events, water would be temporarily stored upstream of the dry dam and slowly decanted to reduce flooding. The dry dam would be designed to store runoff from a 100-year flood below the level of an open channel emergency spillway. The emergency spillway would then be designed to discharge the probable maximum flood (PMF) without overtopping the dam. Rainfall for a 100-year, 6-hour storm is 4.9 inches. Rainfall associated with the PMF is 29.5 inches in 6 hours.

Based on preliminary calculations, the proposed dry dam would reduce the peak flow from a 100-year flood by about 40% in Briceville and 17% in Lake City. Preliminary assessments indicate that TDEC can recommend approval of the dry dam, provided that extensive stream habitat improvements are made as mitigation for the section of stream that will be covered by the dam. The proposed plan will therefore allow for flood reduction and stream habitat improvements, which should be a win-win scenario for all CCWF volunteers and government agencies.

Implementation of positive flood reduction measures in Coal Creek will be an involved process that will require TDEC, TVA, and U.S. Army Corps of Engineers review of plans with other applicable agencies. Adequate funding for implementation is not guaranteed even if a win-win flood reduction plan is developed and permitted by the applicable agencies. We will never know if funding can be obtained until we try. As Rev. Roy Daugherty says: "sometimes you just need to do the right thing and have faith that others will do the same."

Before proceeding with this initiative, input is needed from interested parties. You can email your comments to bthacker2@coalcreekaml.com or attend the community meeting on August 17, 2000 at 7:00 pm (Briceville Elementary School) and deliver your comments in person.

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