Those Dammed Lakes - Hydro-Environmental Analysis: Freshwater Environments - page 309

FIGURE 10.32 Examples of spillway energy dissipation designs. (From USBR, Design of Small Dams , 3rd
ed., U.S. Government Printing Ofice, Washington, DC, 1987.)

d 2

V 1

d 1

F 1 between 1.7 and 2.5
Form A—prejump stage

F 1 between 4.5 and 9.0
Form C—range of well-balanced jumps

Oscillating jet

Roller

F 1 greater than 9.0
Form D—effective jump but rough
surface downstream

F 1 between 2.5 and 4.5
Form B—transition stage

FIGURE 10.33 Characteristic forms of hydraulic jumps as a function of the Froude number. (From USBR,
Design of Small Dams , 3rd ed., U.S. Government Printing Ofice, Washington, DC, 1987.)

issues, which will be discussed in later chapters. One example is dissolved gases, either too much
or too little.
One problem in many areas is total dissolved gas supersaturation (TDGS). The dissolved gas
concentrations in water are a function of pressure (as well as temperature, etc.), such as the par-
tial pressure of the individual gases in the atmosphere. The concentration at which water is in
equilibrium with the atmosphere is the saturation concentration. When air is entrained and the
pressure increases, such as when water falls over a dam into a plunge pool or a jet of water con-
tacts a surface, the concentration can increase well beyond that saturation concentration, or become