WSPC12524 ‎(2)‎

• File Number: 8220.101.10
• Description: Colorado River Water Projects - Glen Canyon Dam-Lake Powell - Adaptive Management
• State: CO
• Basin: Colorado Mainstem
• Date: 3/6/1998
• Author: DOI-GCMRC
• Title: Assessment of Impacts of Glen Canyon Dam Operations on Water Quality Resources in Lake Powell and the Colorado River in Grand Canyon - Grand Canyon Monitoring and Research Center - Draft - 03-06-98
• Water Supply Pro - Doc Type: Report/Study

002258

that the highest conductivity, lowest temperature and lowest dissolved oxygen levels are

discharged from the penstocks, as seen in Lees Ferry water quality (Figs. 12-15). At this point

uplake, the fresh cold bottom plug typically has three options. I) Hypolimnetic Overflow: If the

FRESl:P flow is not sufficiently cold or the chemical gradient between it and the mtlromictic_

salty warm bottom plug is too great, its momentum will carry it over the hypolimnion where it is

entrained by the penstock withdrawal plume suction from dam releases pull it up toward the

penstocks. The penstocks will continue to draw on this layer (as well as others) until the following

winter..when the next SWARM reaches the dam. This is the most common scenario, occurring 14

of the past 33 years. 2) Hypolimnetic Underflow: If it is sufficiently cold and dense, the

FRESCO will continue downlake on the bottom, displacing the hypolimnion upward toward the

penstocks and perhaps not stopping until it reaches the dam if of sufficient magnitude. An

underflow that reaches the dam is the most efficient process for removing meromixis and

restoring oxygen to the hypolimnion without non-powerplant releases. This is also the least

common scenario, occurring only 6 times since Powell's filling (1973,1983,1984, etc.). 3)

Hypolimnetic interflow: Several factors can contribute to this process. If the advective forces are

removed from the bottom currents through diversion to surface flows in the spring, the bottom

currents stall and the plumes substantially slow or cease to move toward the dam. The discharge
from the dam may continue to pull the FRESCO through the SWARM at a depth that corresponds
to the relative density and momentum of the respective flows. Furthermore, if the chemical or
thermal gradients are insubstantial, the FRESCO and SWARM plugs may mix through diffusion
and dispersion. This interflow is more common-occurring approximately 12 of the past 33 years.
The amount of meromictic removal is a function of the depth of the interflow.
Late Winter SCOOL: The final of the three bottom hugging winter plumes, the late winter
SCOOL plug has higher salinity concentrations than FRESCO but is not as cold. There are less of

03/06/98

DRAFT

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