Environmental Engineering Reference
In-Depth Information
1998). The water level is typically maintained or controlled using some structure. Examples include
berms, dams, dikes, and levees, which are constructed to contain water, and are often used to
increase water levels in a wetland or maintain water levels in a stream. Water control structures
such as spillways, pipes with drop inlets, and stoplog water controls are intended to control lows,
and also to control water levels. For example, a spillway, a low point in a berm, provides an escape
for excess water above the designed level. Typically, the water level requirements vary by season so
that lexible control devices are required (FISRWG 1998).
8.4.32 w
eIrS
(r
ock
V
ortex
)
A rock vortex weir is designed to serve as a grade control, primarily preventing changes in
grade. Rock vortex weirs also introduce variable low velocities. During base lows, the lows
are directed around and through the structure, while during high lows, the structure acts like
a weir and tends to form scour pools downstream of the structure while still maintaining the
bed load sediment transport regime of the stream. Rock vortex weirs are typically V-shaped, as
illustrated in Figure 8.49, with the point upstream and the legs at a 15°-30° angle relative to the
streambank.
8.4.33 w
etLand
c
onSerVatIon
(a
nd
r
eStoratIon
)
Wetland conservation typically refers to the protection and conservation of wetlands that are main-
taining wetland functions, while restoration refers to attempts to restore those functions in wetlands
Flow
Top of bank
Footer stones
Weir stones
Flow
Scour area
Weir stone
Footer stone
Scour pool
Profile view
To e of bank
Plane view
Top of bank
Former stream bank
Base flow
Weir stones
Footer stones
Section view
FIGURE 8.49
Rock vortex weir. (From Stormwater Manager's Resource Center. Stream restoration: Flow
delection/concentration practices. Available at: http://www.stormwatercenter.net/.)
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