Rehabilitation of Choccoloccoo Creek Watershed Site 11
Choccolocco Creek Watershed Site 11
Choccolocco Creek Site 11 is a multi-purpose dam constructed in 1971 for the purposes of flood control and municipal water supply. It was designed and constructed as a Significant (Moderate) Hazard dam. Since the dam was constructed, a multi-million dollar water treatment plant and homes have been built downstream which resulted in the dam being reclassified as a High Hazard dam.
The sponsors, the Water Works and Sewer Board of Anniston, Alabama, requested assistance under the Watershed Rehabilitation Program to upgrade the dam to meet current NRCS criteria for a High Hazard structure.
Several alternatives were considered to bring the dam into compliance. The structural measures selected and designed to upgrade the dam consisted of a concrete parapet wall along the top of the dam crest, raising the auxiliary spillway by 0.4 feet; installing a turf reinforcement mat in the auxiliary spillway; placing grouted and loose rock riprap on the downstream toe of the dam, and replacing some metal work on the concrete riser.
The parapet wall raised the top of the dam elevation by 5.3 feet in order to safely contain and surpass the maximum probable flooding level. The riprap placed on the downstream face of the dam protects the dam from flows discharging from the auxiliary spillway.
The existing dam is 75 feet high with a normal pool of 182 surface acres. The drainage are of the reservoir is 15.3 square miles, mostly within Talladega National Forest and Mt. Cheaha State Park. Mt. Cheaha is the highest point in Alabama.
The rehabilitation work was divided into two separate sets of construction drawings. This accommodated the sponsor’s desire to perform a portion of the work for in-kind credit to meet their financial assistance obligations. The sponsors performed all the work on the parapet wall and the auxiliary spillway. The city work crew was experienced in concrete construction and did an excellent job building the parapet. Installation of the riprap toe protection, and metal work replacement was performed under a contract administered by the Water Works and Sewer Board. Work began in both projects in January 2007. The riprap toe protection was completed in November 2007 and the parapet was completed in May 2008.
The Choccolocco Creek Watershed dam is in a much different setting than when it was originally constructed. Over the years, population growth and urban sprawl have occurred both upstream and downstream from the dam, and land use changes have taken place. Upgrades made to the dam will ensure a safe water supply and provide increased safety to occupants of 23 homes and the multi-million dollar water treatment plant that is within the downstream potential flood zone, for at least another 100 years.
A turf reinforcement mat was placed in the auxiliary spillway; grout and loose rock riprap was placed on the downstream toe of the dam, and some metal work was replaced on the concrete riser.
A concrete parapet wall was built along the top of the dam crest, raising the auxiliary spillway by 0.4 feet.