Text C ________

Waves in reservoirs may damage structures and embankments which are located not far from the water. Part of the design of any large reservoir is to estimate wind tide and wave height. Wind tide is caused by the movement of the surface water towards the shore under the action of the wind. Thus hydrostatic unbalance and a return flow at some depth must occur. Wind tides are generally larger in reservoirs that are shallow and have rough bottom. When wind begins to blow over a smooth water surface small waves are caused by the tangential forces between the wind and water. Thus, the waves increase in size and the push of the wind against the back of the wave also increase. As the waves grow in size their speed also increases, until they move with the same speed as the wind. Since the wind forces acting on the wave are a function of the difference between wind speed and wave speed, further growth ceases when the speeds become equal. Waves are critical only when the reservoir has the maximum water level. Thus, in selecting the critical wind speed for reservoirs subject to seasonal fluctuations, only winds which can occur during the season of maximum water level in the reservoir should be considered.

It is virtually impossible to find a reservoir site having complete ideal characteristics. There exist general rules for choice of reservoir sites. They are:

1) A suitable dam site must exist. The cost of the dam is often a controlling factor in selection of a site.

2) The cost of real estate for the reservoir (including roads, railroads, cemetery and dwelling relocation) must not be excessive.

3) The reservoir site must have adequate capacity.

4) A deep reservoir is preferable to a shallow one because of less loss of water as a result of evaporation.

5) Areas which are unusually productive of sediment should be avoided if possible.

6) The quality of the stored water must be satisfactory.

7) Sites from which a considerable quantity of leakage may occur should be avoided.