Those Dammed Lakes - Hydro-Environmental Analysis: Freshwater Environments - page 307

Shape A

Shape B

Shape C

Shape C

FIGURE 10.30 Examples of reservoir conduits and shapes. (From FEMA, Technical manual: Conduits
through embankment dams best practices for design, construction, problem identiication and evaluation,
inspection, maintenance, renovation, and repair, Federal Emergency Management Authority, Washington,
DC, 2005.)

a 128 m-high concrete arch dam on the Zambezi River resulted in an 80 m deep (below the initial
riverbed) downstream scour hole (Mason and Arumugam 1985).
Examples of energy dissipation designs (stilling basins) for spillways are illustrated in Figure 10.32.
These devices are designed to introduce a hydraulic jump, which results from a change in velocities
from supercritical to subcritical lows. Hydraulic jumps result in large and rapid changes in the water-
surface elevation, and a subsequent large decrease in kinetic energy. Examples of hydraulic jumps as a
function of the Froude number are illustrated in Figure 10.33 and dissipation structures are illustrated
in Figure 10.34. For supercritical lows, the Froude number is greater than one and the larger the
Froude number the higher the spillway velocity in relation to the speed (velocity) of a gravity wave.
In addition to dissipating energy, hydraulic jumps also aid in increasing oxygen concentrations
and enhancing mixing.
In addition to dissipating energy by inducing a hydraulic jump, there are a variety of other energy-
dissipating devices or structures. For example, jet releases from pressure conduits are often directed
or delected onto impact-type dissipaters. Impact dissipaters direct the water into an obstruction that
diverts the low and generates turbulence (Wei and Lindell 2004). Examples of jet releases are illus-
trated in Figures 10.35 and 10.36. Strontia Springs Dam, illustrated in Figure 10.35, is owned and
operated by Denver Water and was put into service in 1986. It is a 292 ft. high, double-curvature,
thin-arch, concrete dam with a maximum structural height of 292 ft.