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b. determine the appropriate type and structure design. Select a curtain or earthen/rock fill
weir as the structure. Although rock or stone, sheet pile, and fabric liners are feasible construction
materials, an impermeable fabric material seem to be the least expensive. This however, requires the
designer to consider the substantial force that the cool dense water will exert on the curtain with in
place. Use the numerical model SELECT (Davis, et al 1987) or a numerical water quality model to
estimate the required elevation and dimensions for the outlet device. The thermal stratification history of
the reservoir should be reviewed to determine the lowest elevation of the thermocline which will be the
crest elevation for the underwater dam.
c. Vermeyen (1997) provides guidance on the design, fabrication, installation, and operation of
temperature control curtains based on Bureau of Reclamation experience at 4 reservoirs. Bohac
(1989) also describes a design procedure used by TVA for a submerged curtain constructed at
Cherokee Reservoir. Bohac, Baker, and Shane (1986) present site-specific design information for the
Cherokee curtain.
4.3.3.3 Applications
This relatively new technique has been implemented at several projects in the US Bureau of
Reclamation (USBR) and the Tennessee Valley Authority (TVA). The technique has been successful in
establishing a cool water refuge for fish (Bohac 1989) in Cherokee Reservoir. The Bureau of
Reclamation has successfully employed curtains to control release temperatures at Lewiston and
Whiskeytown Reservoirs in California and the Bureau has designed a control curtain for Shasta Dam.
4.3.3.4 Summary
A submerged weir or temperature control curtain is an outlet structure designed to skim warm
epilimnetic water for release to meet warm temperature requirements downstream or retain cool
hypolimnetic water in the reservoir. In some instance, curtains have been used to skim cool water from
the hypolimnion of reservoir to meet cool-water objectives in the river. The technique was also used to
create a cool-water habitat in a reservoir embayment. Design and construction guidelines are
presented by Vermeyen (1997). Information concerning this technique is summarized in Table 4.3.3.
4.3.4 SUBMERGED SKIMMING WEIR
4.3.4.1 Problem Addressed
The thermal stratification that occurs at most reservoirs can create problems with release water
quality. If the intake structure withdraws water from the hypolimnion, the release may be low in
dissolved oxygen (DO) or contain high concentrations of undesirable trace constituents. In t is case,
withdrawal of water primarily from the epilimnion may be desirable. If the project must release high
discharges, as for a hydropower project, discharge through a port (single port or horizontal line of
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