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.
