Subsequent to the model tests discussed in the main report, the plans for the Oakley Dam project were changed by modification of the spillway design. These modifications involved lowering the elevation of the spillway crest, decreasing the length of the spillway, and extending the gate piers upstream. Prior to the adoption of these alterations, it was thought desirable to determine what effects they would have on discharge characteristics, stilling basin performance, and riprap requirements. Approach flow conditions with the revised spillway installed were generally satisfactory, although the decrease in spillway height increased the velocity along the abutment wraparounds and increased drawdown and contraction in the end bays of the spillway. The capacity of the spillway was adequate; the maximum discharge of 150,000 cfs was passed at a pool elevation of 661.0 with the original abutments and 661.6 with the proposed design abutments. With the spillway reduced in elevation, better energy dissipation was obtained with two rows of baffle piers on the downstream portion of the apron (type 8 basin) rather than with the chute blocks and one row of baffles with the original spillway (type 6 basin). Observations also indicated that a flow of about 35,000 cfs could be passed through the two Rea Road bridges below the structure without overtopping the roadway. It was determined that riprap having an average stone size of 400 lb was required for a distance of 60 ft downstream of the stilling basin; 15-lb stone should suffice for the rest of the exit channel. Additional protection should be provided at the abutments of the Rea Road Bridge and it is recommended that these areas be paved for a distance of 100 ft along the roadway embankment. Protective stone sized to protect against wave action along the upstream embankment should afford adequate protection in the areas of the spillway abutments.
Spillway for Oakley Dam, Sangamon River, Illinois. Appendix A: Type 2 (revised) spillway: Hydraulic Model Investigation
Technical Report ; H-70-13 app.A
1972
2626997
Report
Electronic Resource
English
Spillway for Oakley Dam, Sangamon River, Illinois: Hydraulic Model Investigation
HENRY – Federal Waterways Engineering and Research Institute (BAW) | 1970
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