Dams and Reservoirs - Hydrogeology: Objectives, Methods, Applications - page 285

C HAPTER D4
Dams and Reservoirs
1 GENERAL CHARACTERISTICS
The purpose of these structures is to create surface storage of water
(reservoir), by locally obstructing a valley up to an appropriate level (dam).
Their goals are varied and can be multiple:
• water storage used for electricity production (hydroelectric dams),
• reserves used for irrigation or drinking water supply,
• smoothing of discharge patterns (fl attening of peaks and increased
fl ow during the dry season),
• creation of pleasure lakes.
There are several types of dams:
• gravity dams, in concrete or masonry, support the pressure of the water
they hold back along their entire surface;
• arch dams, made of concrete, transfer the load to the banks;
• embankment dams, made of unconsolidated material or of large blocks
of rock, sometimes in conjunction.
The dimensions and storage capacity of reservoirs varies greatly. The
height of small dams, between a few meters and twenty or so meters,
generally enables the storage of several thousand to several tens of
thousands m 3 . The capacity of the reservoir is, in fact, totally independent
of the dam height, and depends mainly on the topography and surface of
its watershed.
The creation of a reservoir, by signifi cantly altering the hydrogeologic
conditions over the fl ooded area and its shores, can have noticeable effects
on the behavior and the exploitation of infrastructures, as well as on the
surrounding and downstream environments. The increased hydrostatic
pressure in the area, directly dependent on the height of water in the
reservoir, can lead to more or less serious problems: