Environmental Engineering Reference
In-Depth Information
Surface Water intake
Withdrawing water from a lake, reservoir, or river requires an intake struc-
ture. Because surface sources of water are subject to wide variations in
flow, quality, and temperature, intake structures must be designed so the
required flow can be withdrawn despite these natural fluctuations. Surface
water intakes consist of screened openings and conduit that conveys the
flow to a sump from which it may be pumped to the treatment works.
Typical intakes are towers, submerged ports, and shoreline structures.
Intakes function primarily to supply the highest quality water from the
source and to protect downstream piping, equipment, and unit processes
from damage or clogging as a result of floating and submerged debris,
flooding, and wave action. To facilitate this, intakes should be located to
consider the effects of anticipated variations in water level, navigation
requirements, local currents and patterns of sediment deposition and
scour, spatial and temporal variations in water quality, and the quantity of
floating debris.
For lakes and impounding reservoirs where fluctuating water levels
and variations in water quality with depth are common, intake structures
that permit withdrawal over a wide range of elevations are typically used.
Towers (
Figure 5.5
) are commonly used for reservoirs and lakes. A tower
water intake provides ports located at several depths, avoiding the problems
of water quality that stem from locating a single inlet at the bottom, as water
quality varies with both time and depth. With the exception of brief periods
in spring and fall when overturns may occur, water quality is usually best
close to the surface, thus intake ports located at several depths permit selec-
tion of the most desirable water quality in any season of the year (see
Figure
5.5
). Submerged ports also have the advantage of remaining free from ice
and floating debris. Selection of port levels must be related to characteristics
of the water body (Hammer and Hammer, 1996).
Considerations that affect lake intake location include (McGhee, 1991):
• Locate intakes as far as possible from any source of pollution.
• Factor in wind and current effects on the motion of contaminants.
• Provide suficient water depth (typically 20 to 30 feet) to prevent
blocking of the intake by ice jams that may fill shallower lake areas
to the bottom.
River intakes are typically designed to withdraw water from slightly below
the surface to avoid both sediment in suspension at lower levels and float-
ing debris; if necessary, they are also located at levels low enough to meet
navigation requirements. Generally, river intakes are submerged (see
Figure
5.6
) or screened shore intakes (see
Figure 5.7
). Because of low costs, the sub-
merged type is widely used for small river and lake intakes.
