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4.16 CHAPTER FOUR

rivers. The intake system must have adequate capacity to meet maximum water demand
during its projected service life, and intake capacity equal to this demand must be avail-
able during the period of minimum water level in the source of supply.
A conservative approach should be used to establish the lowest water level for intake
system design. Lack of adequate submergence during periods of extreme low water re-
sults in greatly reduced capacity. Deeper than normal submergence should be considered
for rivers subject to floating and slush ice, or where extremely low water may occur dur-
ing the winter season as a consequence of ice jams. On some rivers, it may be impossi-
ble to obtain adequate submergence under all anticipated operational conditions. For such
situations, a low, self-scouring channel dam may be required for a reliable intake system.

Layout
Cellular or parallel component design of intake systems should be evaluated for major fa-
cilities. Cellular design divides the intake into two or more independent and parallel flow
streams. This arrangement enhances reliability, provides flexibility, and simplifies main-
tenance activities. Individual cells can be taken out of service as required for inspection,
cleaning, maintenance, or repair.

Inlet Works and Ports
For intakes located on deep reservoirs and rivers, gated inlet ports may be provided at
several depths to facilitate selective withdrawal of water. In rivers, submergence may gov-
ern, and ports must be placed at as low an elevation as practical. However, the lowest
ports of an intake should be sufficiently above the bottom of the channel to avoid clog-
ging by silt, sand, and gravel deposits. Port inlet velocities should be selected to mini-
mize entrainment of frazil ice, debris, and fish. Factors that affect selection of intake port
configuration and locations are summarized in Table 4.4.
Development of an intake port design should include an overall operational strategy
identifying potential problems that may be encountered and the capability of minimizing
problems by selective withdrawal of water from the water source. It is likely that annual
facility operation will require use of several intake ports in an effort to draw the highest-
quality water. A water quality monitoring system capable of defining water quality pa-

TABLE 4.4 Intake Port Selection
Required port location
Concern (to be avoided) Shallow Intermediate Deep
Organisms (requiring sunlight) ,/ ,/
Warm water ¢" ,/
Storm turbidity ,/ ,/ 4
Plankton ,z ~/
Carbon dioxide 1/
Iron and manganese ,I ~/
Color ,/ ,/