Flood routing criteria should recognize constraints that may exist on the maximum desirable water surface elevation. A limit or maximum water surface reached during a routing of the IDF can be achieved by providing spillways and outlet works with adequate discharge capacity. Backwater effects of floodflow into the reservoir must specifically be considered when constraints on water surface elevation are evaluated. Sediment deposits in reservoir headwater areas may build up a delta, which can increase flooding in that area, as well as reduce flood storage capacity, thereby having an effect on routings. Reservoir Regulation Requirements.
Reliability depends upon structural competence and availability for use.
Availability and reliability of generating units for flood release during major floods should be justified. Availability of a source of auxiliary power, for gate operation, effects of reservoir debris on operability and discharge capacity of gates and other facilities, accessibility of controls, design limits on operating head, reliability of access roads, and availability of operating personnel at the site during floods are other factors to be considered in determining whether to assume release facilities are operational. A positive way of making releases to the natural watercourse by use of a bypass or wasteway must be available if canal outlets are to be considered available for making flood releases. Bypass outlets for generating units may be used if they are or can be isolated from the turbines by gates or valves. In flood routing, assumed releases are generally limited to maximum values determined from project uses, by availability of outlet works, tailwater conditions including effects of downstream tributary inflows and wind tides, and downstream nondamaging discharge capacities until allocated storage elevations are exceeded.