A07_-_IMCOM_OPORD_17-036_(HWAD-Black_Beauty).pdf

including an asphalt membrane and pipe sub drain).

A second rehabilitation program began in June 1957 to replace the reservoir -;lope lining with an impervious silt blanket and a gravel cover. The reservoir was full again by September 1957.

Two breaks of the outlet pipe occurred in J\farch 1974 and October 1978. In Febrnary 1979, the l)Utlet pipe w:L, excavated for repair.

BlaL"k Beauty Dam and Reservoir is located about 4 miles northwest of Hawthorne in an alluvial fan deposit near the base of the Wassuk Mountain Range. The reservoir wa,; corn,tructed by a combination or cut and lill of :11luvial materials to form a rcc1m1gular bowl set into the sloping ground and surrounded by earth embankment on three sides. The reservoir is 52 feel deep and measures approximately 500 by 600 feet. The reservoir is lined with "impervious" fine-grained soil covered by an m,phalt membrane. The liner is prolected by three. progressively coarser layers of granular soil. The outer layer is I :2-ind1 minu-;

stone which serves :1s slope protection.

6. Outlet Works.

No compuHltions were m:1de to estimate innow and outflow capacities of the pipelines. Cal Creek and Rose Creek Dams discharge to Black Beauty Reservoir. Therefore. it seems likely that the minimum inflow capacity to Black Beauty is about 4,500 gpm.

7. Spillway The �pillway serves as an emergency structure lo prevent ovellopping the dam should pipe inflow from other sources exceed the outflow release due to mis-operntion or a breakdown in the distribution system. There is no overland nmoff into the reservoir. The spillway consists of a r rect.mgula concrete channel 3.0 feel wide by 3.5 feet deep with a 0.5 foot high concrete sill at the intake. The elevation of lhe sill is 3.0 feet below the lop of the dam. There is a fine trnsh screen located across the spillway intake. The spillway channel extends through the dam embankment and is covered at the access road. On the reservoir 5ide of the access road there is a wood-flap g,1te for keeping small animals from entering the reservoir through the spillway channel. After passing under the access road the channd turns downo;lope and steepens. The spillway terminates well downslope from the access road.

The spillway crest elevation and invert elevations of the concrete cliannel were estimatetl from reservoir topography taken in May 1979. The spillway crest elevation wa� taken at 4678.9 feet. The invi:11 elevation of the concrete channel at the inta"-e is 4678.4 feet. decreasing to an estimated elevation of 4677.5 at JOO feet dowmarcam of the intake. The exit channel lhen turns downslope for

35 feet, ending at invett devation 4676.8 feet. The slope of the concrete channel is supercritical for the range of discharges that the spillway controls. I I lt!refore, the exit channel does not cause submergence of the spillway crest. With the screen at the spillway crest in place (assuming 50 percent net opening) the estimated spillway discharge capacity is 30 cf s ( 13.400 gpm). This exceeds e of no more: than a small number of inhabitable !-.truclures, 1he dam Cl.luld be das-.it'ied as "signilic:111t" or it could be classified "low" if there are no inhabitable structures inundated.