Stilling Basin Modifications, Bull Shoals Dam, White River, Arkansas: Hydraulic Model Investigation
Abstract
Damage to the Bull Shoals Dam stilling basin was observed immediately downstream from the conduits after about one year of operation. To assist in determining the causes of this damage and devise modifications that would correct the situation, tests were initiated on a 1:12-scale conduit model and a 1:50-scale section model of the spillway. An upward-sloping ramp, replacing the first three steps of the stilling basin, proved most feasible as the basic scheme for permanent repairs to the prototype. Large and rapid pressure fluctuations still occurred at the upstream end of this ramp for conduit discharges but average pressures were positive. High dividing walls between the conduits reduced pressure fluctuations on the stilling basin floor with tailwater elevations as high as 458.0, but were not effective for higher tailwater elevations. The present 4-ft-high end sill was found inadequate for dissipating energy from conduit flows when the smooth floor ramp was installed. Raising the end sill height to 10 or 12 ft caused retention of deeper tailwater in the basin and resulted in improved stilling action. The higher end sills produced an adequate hydraulic jump under spillway discharge, but were somewhat less effective than the low end sill in preventing erosion in the exit channel. For passage of extremely low flows, some protection below the high end sill is required. Baffle piers provided improved stilling action for spillway flows, but were of negligible value for conduit discharges. When used in conjunction with a 10- or 12-ft-high end sill, baffle piers of 8-ft height were found to be the most efficient. The modification selected for construction in the prototype consisted of vertical-faced baffle piers, 8ft in height, located 50.ft upstream from the original end sill.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1958
- Accession Number
- ADA637644