State recommends repairing Black Bass Dam

Black Bass Dam -- Arkansas Natural Resources Commission Deputy Director/Chief Engineer Jon Sweeney examines the downstream face of Black Bass Dam during an inspection made in April with county and state officials. His May 29 report noted areas of seepage, a cavity below the emergency spillway and other hazards. He made several recommendations for repair and further assessment. Photo by Kathryn Lucariello [Order this photo]

EUREKA SPRINGS -- The City of Eureka Springs will soon be faced with repairing Black Bass Dam in light of a letter from the Arkansas Natural Resources Commission (ANRC).

The letter, dated May 29, came to Carroll Count Judge Richard Williams from Jon Sweeney, ANRC's deputy director/chief engineer.

Sweeney visited the dam in April, along with Williams and Carroll County Office of Emergency Management Coordinator Mike Harris; ANRC Dam Safety/Floodplain Management Engineering Supervisor Alvin Simmons; Senator Blanche Lincoln's assistant, John Hicks; and Congressman John Boozman's assistant, Sarah Hartley.

Judge Williams has been involved in this issue because the safety of some of its downstream residents, should the 112-year-old dam fail, falls under the purview of the county's emergency management plan.

Heavy rains in March forced the evacuation of tourists staying in a cabin below the dam, as torrents of water poured over the spillway and made the creek flood downstream, cutting off the cabin from the road.

The dam is not currently "permitted," meaning it does not come under the authority of the ANRC because of its low impoundment of water. However, according to the City of Eureka Springs Web site, the dam is on the National Register of Historic Places as an individual listing. Judge Williams said his understanding is that it must be repaired and preserved because of that classification.

'High hazard'

Sweeney's letter noted observations from the visit in April and outlined several recommendations.

He says the dam is classified as "high hazard."

"A cavity was observed in an area just below the right emergency spillway wall. Areas of seepage were observed on the downstream slope. The downstream end of the emergency spillway floor was unsupported. Stone has become dislodged from the downstream slope in several locations."

His recommendations were to fill the cavity, add material to support the downstream end of the emergency spillway floor and elevate the right side of the emergency spillway wall nearest the dam to an elevation equal to the crest elevation of the dam.

He recommended monitoring the seepage from the downstream slope.

"Any increase may be indicative that material is beginning to wash through the dam," he said.

Sweeney recommended contracting with an engineering firm experienced in dam safety issues.

"The consultant should perform a detailed stability evaluation of the dam including the necessary hydrologic/hydraulic computations. In addition, the consultant could develop a comprehensive renovation plan, including cost estimates for this dam."

He also suggested developing an emergency action plan for the structure and downstream residents.

In his e-mail to the judge, Sweeney noted, "There are two possibilities we did not put in the letter. The dam may not require a high hazard rating if a downstream inundation study were performed. A modern hydrologic and hydraulic study (including potential effects on Lake Leatherwood) might show that a high hazard classification is not needed.

"Permitting could be required if requested by a downstream landowner -- even if the dam were no longer classified as high hazard. This is because permitting is required if lives or property would be endangered, while high hazard classification requires probable loss of life or a very large monetary loss."

Downstream issues

A topographical map shows West Leatherwood Creek running from the dam through about a five-mile stretch and emptyping into Lake Leatherwood, which has a spillover dam at its far end.

Officials also visited that dam in April. Eureka Springs' emergency action plan notes that significant rainfall within a certain period of time could affect that dam. A breach in Black Bass Dam may or may not have significant impact on the Leatherwood dam. There are several residents along the five-mile stretch of the creek to Lake Leatherwood.

City departments are still in the process of reviewing the report. Public Works Director Dwayne Allen said the city had spoken with dam engineer Dee Purkypile of Texas, who is in the process of moving to Eureka Springs and has agreed to do engineering work on Black Bass Dam.