HY8:Stilling Basins
The four types of Stilling Basins External Energy Dissipators available in the program:
The maximum width of an efficient 'USBR' type stilling basin is limited by the width that a jet of water would flare naturally on the basin foreslope. The user is given the maximum flare value and is prompted to enter a basin width smaller than this value. If a 'SAF' basin is used, the basin width is set equal to the culvert width and the user is prompted to choose either a rectangular or flared basin depending on site conditions. Stilling Basins resemble the following illustration.
Variables from the figure
- W0 -- width of the channel
- WB -- Width of the basin
- y0 -- Culvert outlet depth
- Y1 -- Depth entering the basin
- Y2 -- Conjugate depth
- S0 -- Slope of the channel
- ST -- Slope of the transition
- SS -- Slope leaving the basin
- Z0 -- ground elevation at the culvert outlet
- Z1 -- ground elevation at the basin entrance
- Z2 -- ground elevation at the basin exit
- Z3 -- Elevation of basin at basin exit (sill)
- LT -- Length of transition from culvert outlet to basin
- L -- Total basin length
- LB -- Length of the bottom of the basin
- LS -- Length of the basin from the bottom of the basin to the basin exit (sill)
- Tw -- Tailwater depth leaving the basin
Warning for Stilling Basin Width
Since the maximum basin width is a function of basin depth, the maximum width may decrease as the program increases the basin depth while converging on a solution. Therefore the maximum basin width may fall below the user's first choice for basin width. In this case, the user will be prompted for a new basin width.
