PROJ00345 - Laserfiche WebLink

Home Browse Search

I I I ~ ~ I I I I I I I I I I I I I I I I D. Spillway General. Adequate design spillway capacity, unrestricted flow, and con- trolled discharge are obviously key considerations in overall project safety. Recommendations are limited to the geotechnical aspects of spillway design and operation as hydrologic and hydraulic studies are beyond the scope of the review. It is understood that the inflow design flood has been reviewed by others. Approach Channel. Excavated side slopes up to 50 feet high are shown on the drawings at 1.5:1. Considering the effects of the high water table and possible toe erosion during discharge, flatter slopes are recommended. Slopes of 3:1 or 2:1 with a bench at mid-height are recommended to insure against a slump or extensive ravelling which could restrict spillway flow. Discharge Channel. Although no data were available on discharge fre- quency or velocities, the 1.5:1 riprapped side slopes could not be expected to withstand prolonged high velocities or turbulence. Assuming, however, that the design is adequate for normal discharges and frequency of use, no modifications are recommended. If not adequate for normal flows, either grouting of the riprap or the use of large size armor stone should be con- sidered. These comments are based on the concept that it is probably im- practical to design against all damage which could result from the maximum probable flood. The essential point is that such damage would be limited to the spillway discharge area and would not endanger the dam or the abut- ments. Inspection of the Coal Creek streambed,indicates that while extremely high flows would cause substantial erosion, the channel would contain the discharge until it was safely past the damsite. E. 'Shoreline. 'Criteria. In evaluating shoreline stability it was assumed that the primary concern would be a massive slide which could cause substantial damage. This damag~ could range from loss of a portion of the relocated road to