HAZARD: DAM FAILURE
DAM FAILURE PROFILE:
Dam failure refers to a collapse, overtopping, breaching or any related condition that causes downstream flooding. Approximately one-third of all dam failures are caused by overtopping due to inadequate spillway capacity, one-third are caused by seepage through or under the structure, and the remainder from improper design or construction or because of earthquake or landside events which trigger the failure of the dam. Examples of dam failure in the United States include the Johnstown Flood in 1889 resulting in 2209 deaths, the Saugus, California dam collapse in the Los Angeles Aqueduct system in 1928 resulting in 450 deaths, and the Teton Dam breach on the Snake River in Idaho during a flash flood in 1976 resulting in 11 deaths. During Hurricane Agnes in 1972, concern about the Conowingo Dam on the Susquehanna River led to the opening of all flood gates to release pressure when the water level was three feet higher than the dam’s rated capacity.
COUNTY PERSPECTIVE AND HISTORY:
According to the Maryland Department of the Environment, Garrett County has 28 dams, of which 11 are rated as high hazard dams as shown on Figure 33. The Maryland Hazard Analysis rates Garrett County’s composite risk for dam failure at 4 on a scale of one to five. The county’s planning committee agrees with this risk. The largest dams in the county include the Savage River Dam, the Bloomington Dam on the Potomac River, and the Deep Creek Lake Dam as shown on the map on Figure 34. Smaller dams include the Piney Creek Dam and the New Germany Dam. Two other dams of significance to the county include the Mt. Storm Dam and the Stony River Dam, both of which are on the Stony River, a tributary of the Potomac in West Virginia. Failure of either of these dams would affect the downstream communities of Kitzmiller and Bloomington and would also impact the Bloomington Dam.
MUNICIPAL PERSPECTIVE:
As noted above, the town of Kitzmiller is downstream from both the Stony River Dam and the Mt. Storm Dam. In addition, the town of Friendsville is located downstream from the Deep Creek Lake Dam. Finally, six flood control impoundments constructed by the Soil Conservation Service in the 1970’s are located upstream of parts of Oakland, Mountain Lake Park, Loch Lynn Heights and Deer Park in the Little Youghiogheny Watershed as shown on Figure 34. All other municipalities are located on high ground above dam structures.
PREVIOUS MITIGATION EFFORTS:
In 2001, Garrett County joined with Allegany county and Mineral County to institute a telephone warning system for communities downstream of the Savage River and Bloomington Dams. This system has since been expanded to include the entire county for all hazards.
The Savage River and Bloomington Dams are maintained by the Upper Potomac River Commission and are subject to regular inspection and maintenance by the Corps of Engineers. All dams are subject to inspection by the state through its Dam Safety Program, and by the Corps of Engineers.
In addition, the Garrett Soil Conservation District has initiated studies of the flood control dams in the Little Youghiogheny Watershed. Studies of Dams 1, 2 and 3 in Oakland are complete, while the study of Dam 7 above Deer Park is in preliminary form. Figure 51 and Figures 55 through 65 show the inundation areas and the number of structures potentially affected by the major dams in Garrett County. Future studies of Dam 5, upstream from Oakland, and Dam 6 (Broadford Lake) will provide maps showing the inundation area should either of these dams fail.