Environmental Engineering Reference
In-Depth Information
FIGURE 8.17
Aerial photo of a portion of Tucson, Arizona, ca. 1970. Three flood zones are delineated by escarpments and
terraces. (From Ward, J.S., Special Publications, J.S. Ward & Associates, Caldvell, New Jersey, 1975.)
Flood-control dams
constructed upstream serve as storage reservoirs and are the most
effective construction solution to flood protection. They are often designed for multipur-
pose uses including hydropower, water supply, and recreation. They are costly to con-
struct, however, and their number and location require careful study to avoid such
catastrophes as that at Rapid City, South Dakota, described previously.
8.3
Subsurface Water (Groundwater)
8.3.1
Occurrence
General Relationships
A portion of the precipitation runoff enters the ground by infiltration, percolating down-
ward under the force of gravity through fractures and pore spaces, which below some
depth attain saturation or near saturation.
Porosity
relates the percentage of pore space to the total volume (see
Table 3.6)
and rep-
resents the capacity of material to hold water when saturated. Values for various materi-
als are given in
Table 8.1.
