Lower Valle Mines Dam is classified as small, based on its storage capacity of 78 ac-ft. The dam is 22 ft in height. The small dam classification applies to dams between 25 and 40 ft high, or those with storage volume between 50 and 1000 ac-ft. The St. Louis District, Corps of Engineers, has classified this dam as having a high hazard potential; we concur with this classification. The estimated damage zone length extends approximately two miles downstream of the dam. Within this estimated damage zone are two improved roads, the dam and reservoir at Lake Valle, and numerous vacation and permanent dwellings on the shores of the lake. The potential for loss of life and property may be high in the event of a dam failure. Lower Valle Mines Dam is an earth dam, densely vegetated with brush and trees. There are two spillways, the main spillway on the left or west abutment and the auxiliary spillway on the east abutment. The visual inspection and evaluation of available data indicate Lower Valle Mines Dam is in generally fair condition. This judgment is based on the potential for overtopping, and the dense vegetation on the downstream face of the embankment. The embankment materials appear moderately erodible, both the vegetation presently offers some erosion protection. Seepage in the area beyond the toe of the dam does not appear to pose a hazard to the dam at this time. The lack of periodic inspections and maintenance on the dam is considered a deficiency.

The Upper Valle Mines Dam is an abandoned tailings dam constructed to impound sand, silt and clay tailings produced by the milling of barite ore. The dam is reported to be primarily an earth embankment with a relatively thin mantle of gravel-size tailings (chat), and cobble- to boulder-size bullrock. Both the upstream and downstream faces of the dam are heavily vegetated with brush and trees up to 18 in. diameter. The reservoir is nearly filled with fine tailings. Much of the impoundment area is densely vegetated with brush and trees. The spillway is a broad trapezoidal notch cut at the left abutment. The notch is cut into the native soil and will likely be moderately erodible during periods of flood flow. The visual inspection and evaluation of available information indicate the dam is in generally poor condition. This judgment is based on the inability of the spillway to pass the 1 percent probability-of-occurrence (100 year) flood without overtopping the embankment, the hazard of erosion posed to the embankment in the event of overtopping, the dense vegetation on the embankment, as well as the steep slopes and evidence of limited past slumping on the downstream face of the dam.

This report was prepared under the National Program of Inspection of Non-Federal Dams. This report assesses the general condition of the dam with respect to safety, based on available data and on visual inspection, to determine if the dam poses hazards to human life or property. (Author).

Fon-du-lac Subdivision Dam was inspected by an interdisciplinary team of engineers. The purpose of the inspection was to make an assessment of the general condition of the dam with respect to safety, based upon available data and visual inspection, in order to determine if the dam poses hazards to human life or property. Failure would threaten the life and property of ten families and cause appreciable damage to two county roads. Our inspection and evaluation indicates the dam is deficient in that the spillway is inadequate. The guidelines for a dam having the above size and hazard potential require that the spillway be capable of passing a one-half PMF (Probable Maximum Flood). The Probable Maximum Flood is defined as the flood discharge that may be expected from the most severe combination of critical meteorologic and hydrologic conditions reasonably possible in the region. Considering the small volume of water impounded, the large floodplain downstream and the three groups of farm buildings downstream, one-half PMF is the appropriate spillway design flood. A 20% PMF will begin to overtop the dam. The lake and spillway are adequate to contain a 1% annual probability flood (100-year flood) without overtopping the dam.

This report was prepared under the National Program of Inspection of Non-Federal Dams. This report assessess the general condition of the dam with respect to safety, based on available data and on visual inspection, to determine if the dam poses hazards to human life or property. (Author).

This report assesses the general condition of the dam with respect to safety, based on available data and on visual inspection, to determine if the dam poses hazards to human life or property. The St. Louis District has classified this dam as unsafe because of a large seep on the downstream embankment slope near the left abutment contact, and a seriously inadequate spillway that will pass only 32 percent of the Probable Maximum Flood.