2. Gate tower, screens and controlling devices.
3. Sluiceways for silt or sand.
4. Wasteway channel or weir.
5. Cover, settling basin, aerating devices, etc.
Some of these are necessary and common to all classes of reservoirs, while others are employed only in special cases, as for domestic water supplies. All reservoirs formed by earth embankments must have at least two of these, namely a wasteway, which is its safety valve, and outlet pipes or outlet tunnel.
It may be stated that the proper location and construction of the outlet for a reservoir are of vital importance, since either to improper location or faulty construction may be traced most of the failures of the past. It is almost impossible to prevent water under high pressure from following along pipes and culverts when placed in an earth dam. The pipes and culverts frequently leak, and failure ensues. Failure may result from one or more of the following causes:
1. By improper design and placement of the puddle around the pipes.
2. By resting the pipes upon piers of masonry without continuous longitudinal support.
3. By reason of subsidence in the cuts of the embankments and at the core walls, due to the great weight at these points.
4. Leakage due to inherent defects, frost, deterioration, etc.