In determining the character and suitability of materials for constructing a dam it is necessary to make a careful study of the soil and geological formation. This is best accomplished by digging numerous test pits over the basin, especially in the vicinity of the proposed dam site; borings alone should never be relied upon for this information. For such an investigation the advisability of borrowing material for dam construction from the reservoir basin is determined. The porous character of the subsoil strata, or the dip and nature of the bed rock, may forbid the removal of material from the floor of the basin, even at a remote distance from the dam site. The area to be flooded should be cleared and grubbed more or less thoroughly, depending again upon the use for which the water is impounded. In no instance should timber be left standing below the high-water level of the reservoir; and all rubbish liable to float and obstruct the outlet tunnel and spillway during a time of flood should be removed. The accessories to a reservoir, to which reference has been made, may be enumerated as follows: 1. Outlet pipes or tunnel. 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.