CHAPTER II.
Preliminary Studies and
Investigations.
The preliminary studies and investigations which should be made prior to the construction of any dam for the storage of water have to do with (1) the Catchment Area, (2) the Reservoir basin, and (3) the Dam site.
Catchment Area.
It is thought desirable to define a number of terms as we proceed, for the purpose of correcting erroneous usage and for a clearer understanding of the subject. The catchment area of a reservoir is that portion of the country naturally draining into it. The watershed is the boundary of the catchment area and may be correctly defined as the divide between adjacent drainage systems. In regard to the catchment area it is necessary to determine:
1. Its extent and area in square miles.
2. Its topography or the character of its surface.
3. Its hydrography or precipitation and run-off.
4. Its geology, or the character of its soils and subsoils, and the nature and dip of its rock strata.
5. Its flora, or the extent to which it is clothed with forest trees or other vegetation.
All of these elements affect the volumes of maximum run-off, which is the one important factor in the construction of earth dams that must not be underestimated.