CEMP-E
TI 814-01
3 August 1998
CHAPTER 7
INTAKES
7-1. GENERAL. The intake is an important feature of surface-water collection works. For
fairly deep streams, whose flow always exceeds water demands, the raw water collection
facilities generally consist of an intake structure located in or near the stream, an intake
conduit and a raw water pumping station. Often the intake and pumping station are combined
in a single structure. On smaller, shallow streams, a channel dam may be required to provide
adequate intake submergence and ice protection. Inlet cribs of heavy-timber construction,
surrounding multiple-inlet conduits, are frequently employed in large natural lakes. For
impounding reservoirs, multiple-inlet towers, which permit varying the depth of withdrawal, are
commonly used. Hydraulically or mechanically- cleaned coarse screens are usually provided
to protect pumping equipment from debris. Debris removed from screens must be hauled to a
landfill or other satisfactory disposal site. It may be necessary to obtain a permit for
construction of an intake from both State and Federal agencies. If the stream is used for
navigation, the intake design should include consideration of navigation use and of impact
from boats or barges out of control. A permit from the U.S. Army District Engineer is required
for any construction on navigable waterways.
7-2. CAPACITY AND RELIABILITY. The intake system must have sufficient capacity to meet
the maximum anticipated demand for water under all conditions during the period of its useful
life. Also, it should be capable of supplying water of the best quality economically available
from the source. Reliability is of major importance in intake design because functional failure
of the intake means failure of the water system. Intakes are subject to numerous hazards such
as navigation or flood damage, clogging with fish, sand, gravel, silt, ice, debris, extreme low
water not contemplated during design, and structural failure of major components. Many
streams carry heavy suspended silt loads. In addition to suspended silt, there is also a
movement of heavier material along the bed of the stream. The intake must be designed so
that openings and conduits will not be clogged by bed-load deposits. An additional problem,
caused by suspended silt and sand, is serious abrasion of pumps and other mechanical
equipment. Excessive silt and sand may also cause severe problems at treatment plants.
Liberal margins of safety must be provided against flood hazards and also against low-water
conditions. A depression dredged in the stream bed to provide submergence is not a solution
to he low-water problem because it will be filled by bedload movement. A self-scouring
channel dam may be the only means of assuring adequate water depth. As an alternative to
unusually difficult intake construction, gravel-packed wells and horizontal collector infiltration
systems located in the alluvium near the river are often worthy of investigation. Water
obtained from such systems will usually be a mixture of ground water and induced flow from
the stream.
7-3. ICE PROBLEMS. In northern lakes, frazil ice (a slushy accumulation of ice crystals in
moving water) and anchor ice (ice formed beneath the water surface and attached to
submerged objects) are significant hazards, while on large rivers, floating ice has caused
damage. Intake design must include ample allowances for avoiding or coping with these
hazards. The intake location and inlet size are important aspects of design. Excessive inlet
water velocities have been responsible for major clogging problems caused by both sand and
7-1