Page 108 - Water and wastewater engineering

INTAKE STRUCTURES 3-5

TABLE 3-2
Types of intake structure
Category Design type Remarks
Exposed Tower integral with dam Applicable to large systems, expensive
Tower in lake Navigational impact
Shore inlet Design for floating debris and/or ice
Floating or movable Good access for O&M a
Siphon well Applicable to small systems, flexible, easy
to expand
Submerged Plain-end pipe or elbow Applicable to small systems
Screened inlet crib No navigational impact
No impact from floating debris or ice b
Not flexible
Difficult O&M a
Gravel-packed well(s) No navigational impact
No impact from floating debris or ice b
Must have favorable geology
Horizontal collection systems (also No navigational impact
called infiltration gallery or No impact from floating debris or ice b
infiltration bed) Must have favorable geology
a
O&M operation and maintenance.
b
With sufficient depth, ice impacts are minimized.
Adapted from Foellmi, 2005.

Lakes and Reservoirs. Because of their navigational impacts as well as severe winter weather
and consequent difficulties in their operation and maintenance (O&M), exposed structures are
not often used in the Great Lakes and other large cold-climate lakes. On the other hand, exposed
intake structures have been widely used in more warm-climate lakes and in reservoirs. A classic
tower design ( Figure 3-3 ) includes multiple intake ports at different elevations, screens for each
port, and access for maintenance. The tower may be divided into two sections or cells to provide
redundancy. It is accessed by a bridge, causeway, or boat.
Submerged intake structures avoid many of the problems of the exposed systems but are
significantly more difficult to maintain because of lack of access. On the other hand, the lack of
exposed mechanical parts lowers the amount of maintenance time required. A typical submerged
inlet structure is shown in Figure 3-4 . With a favorable geologic strata of sand and gravel on the
shore or the bottom of the lake or reservoir, either an infiltration gallery as shown in Figure 3-5
or a horizontal collection system (called a “Ranney well” after its inventor) under the lake bottom
( Figure 3-6 ) may be appropriate.

Rivers. Both exposed and submerged inlet structures have been used in rivers. In large rivers
that are controlled by locks and dams, the variation in flow and consequent variation in water
surface elevation are of less concern than in unregulated waterways. For most water supplies,