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Claiborne Parish Watershed District |
Needed:
Auxiliary Spillway for Lake Claiborne Dam 
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Contents
In 1991, a flood caused
extensive damage to the 40 mile shoreline of Lake
Claiborne and to public and private properties in the
drainage area of the lake. The dam was described as
shaking by those walking atop it, and after the flood, a
layman diver reported a cavernous erosion at the base of
the dam. Residents are concerned that the potential
water surface elevation of the lake is such that there
may well be again a discharge that overwhelms the
capacity of Lake Claiborne Dam's existing outflow
controls, and that erosion in the event of such a flood
may endanger the earthen dam itself. At the request of
the Claiborne Parish Police Jury, the Louisiana
Department of Transportation and Development completed a
feasibility study for structural modifications that will
limit surcharge water level rise from the current 6.3
feet to approximately two feet for the "100 year
storm." The study used design technology and
safety requirements that have been updated since the
construction of Lake Claiborne Dam 32 years ago.
Table 1 Lake Claiborne In Louisiana Act 299 of the Louisiana State legislature, passed in 1964, created the Claiborne Parish Watershed District as a political and budgetary unit of the state and also provided for "[t]he creation and maintenance of Lake Claiborne within the district for the purpose of conserving the soil and water and developing the natural resources and wealth of the district for sanitary, agricultural, industrial and recreational purposes..." A Board of Commissioners, appointed by the parish Police Jury, was granted the right to regulate improvements "within one (1) mile from the 185.0 foot contour shoreline of Lake Claiborne." Construction of Lake Claiborne and the Lake Claiborne Dam was completed in 1967. The lake is located at the southeast corner of the town of Homer on Bayou D'Arbonne, a tributary of the D'Arbonne River. The lake inundates land in Claiborne Parish only. It has a drainage area of 133 square miles. At full reservoir level, Lake Claiborne has a surface area of 6400 acres. Normal pool elevation is 185 feet above mean sea level. Lake Claiborne is located in the gently rolling upland hills of northwestern Louisiana. One of the area's most scenic sites, it attracts more than 120,000 visitors a year. The lake was designed for sportsmen. At its beginning, the land to be covered by water was cleared of trees and other obstructions to assure maximum skiing and boating pleasure. Later, the lake was stocked with largemouth bass, bluegill sunfish, channel catfish, black crappie, striped bass, and walleye fingerlings. Facilities for camping, fishing, boating, and picnicking were added when the 600 acre Lake Claiborne State Park was created. Along the park's 100 acre wooded shoreline are more than 100 picnic sites with tables and grills, a large covered shelter, restrooms, a boathouse, a concession stand, and a beach. The park's 87 unit camping area includes comfort stations, dump stations, a laundry, electric and water hookups, picnic tables and barbeque grills. A primitive camping area is available for groups, such as Scouts. There are ten modern cabins as well. More than 65,000 people visit the park each year. Because of the demand, plans are underway to expand programs at the state park. Anglers, too, are frequent visitors to the lake. Louisiana's fifth and sixth largest striped bass on record were caught from Lake Claiborne. Recent studies show that Lake visitors have an important economic impact for the locality and the state. Since Lake Claiborne's construction, 1000 homes have been built in the area. Many of the new residents are retirees, who bring in an average annual income of more than $50,000 as well as diverse knowledge and expertise. Lake residents provide about 15% of Claiborne Parish's total tax base. Their local spending strengthens the local economy and adds to state taxes. Lake Claiborne attracts some industry and has the potential for attracting more. Presently there are restaurants, gas stations, convenience stores, and an RV park, all supporting tourism. Recreational programs, assisted living arrangements, and retirement communities are possibilities. top
When Lake Claiborne Dam and Lake Claiborne were designed in the 1960s, engineers used available rainfall and weather data to predict the worst-case flood Mother Nature might reasonably create, that is, the "probable maximum flood." During such a predicted rainfall, the lake would completely fill and water would continue pouring through the spillway without flooding surrounding lands or jeopardizing the structure of dam. Design technology and safety requirements of that time were used to ensure the dam was structurally sound and had adequate storage and spillway capacity to withstand the "probable maximum flood." The earthen Lake Claiborne Dam is 5500 feet in length with a top elevation of 202 feet MSL. The outlet works consist of a 62 foot-diameter circular drop-inlet spillway with a crest elevation of 185 feet, MSL, three 9.5'x14' concrete outlet conduits, and two 8'x8' drawdown gates with an invert elevation of 151.2 feet MSL. As part of the circular spillway, the gates offer no additional water outlet. At the northern end of the dam, there is an all earthen structure (without impervious core) lower than the dam's surface, designed as an emergency spillway in the event of the "probable maximum flood." This spillway would provide water outlet only when the lake level rises to approximately 11 feet above normal pool level. Today, employing updated design technology, it is calculated that the "design storm" discharge (based on 15" rainfall in 24 hours, considered the worst storm possible) would produce an estimated maximum surcharge elevation of 198 feet, that is, 13 feet above normal pool level. The more likely "100 year storm" (10" rainfall in 24 hours) would produce a surcharge 6.3 feet above normal pool level. top In 1991, a 12" rainfall over 24 hours caused Lake Claiborne to rise more than seven feet above its normal pool elevation and a half foot above the "100 year storm" flood elevation. Two hundred homes in the lake area were flooded, with extensive property damage and loss. Schools were closed because bridges and roads were washed out or hazardous. Forty-two roads were closed, including three state highways. Crops were destroyed, and cattle were stranded in flooded fields. Boat traffic was closed. Wildlife and Fisheries agents helped bring to dry land floating butane tanks, satellite dishes, boats, and gas tanks. Crews had to travel by boat to cut off electricity to some homes. Some residents on Lake Claiborne were without electricity for days.
top If the Lake Claiborne Dam remains in its current state, a "design storm" would cause far more damage than the flood of April 1991. Approximately two-thirds of the 1000 homes that have been built in the lake area since the lake was constructed would be flooded. Major damage to roads and bridges would cost a great deal to repair. Dissolution of the earthen portion at the northern end of the spillway (the emergency spillway) would cause a catastrophe downstream and destroy much of Lake Claiborne in the process. top The scenario described immediately above cannot be allowed to happen, so at the request of the Claiborne Parish Police Jury, in March 1998 the Louisiana Department of Transportation and Development approved a study to identify the best possible economical alternative to prevent flooding and damage to the dam. The study, completed in August,
1998, showed five combinations of spillway and gated
outlets that would triple peak discharge out of the lake,
thereby limiting the surcharge water level rise to
approximately two feet for a "100 year
storm." Comparison data for the alternatives
are as follows:
top Of the alternatives, the
shorter spillway (1000 feet') with more gates (12) is the
least top There would be no change in the way
Lake Claiborne is operated from day to day. The
Public Benefits of Auxiliary Increased Outlet Capacity at Lake Claiborne Dam Improved flood control would be the
major public benefit from increasing the outlet
top 1. Louisiana State Legislature and
Office of the Governor of the State of Louisiana.
Louisiana 2. Louisiana Department of
Transportation and Development. Lake Claiborne
Surcharge 3. Louisiana Office of State Parks,
Lake Claiborne. . .the Outdoor Pleasure Never Ends
4. Newpapers dated April 18, 1991
through May 2, 1991, including The Guardian Journal
Claiborne Parish Watershed District, P.O. Box 266,
Homer, LA 71040 |
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