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

OD2295
involving advective movement. Entrainment also involves advective movement that incorporates

water from adjoining masses of water.

2. Seasonal Patterns seen at lake Powell

All the above properties come to bear on the mixing.and.stratification'1)fL-ake-Powell's

waters. Traditional categories of epilimnion, metalimnion and hypolimnion tend to oversimplify

the stratification of Lake Powell, which can have up to 4 or 5 chemoclines and several

thermoclines separating various flows. Differences in stratification occur in a temporal dimension

as well as vertical and longitudinal. The following describes the dominant seasonal inflows and

circulation cells of Lake Powell (bottom panel, Fig 1). Timing of these events can typically vary a

month or more in either direction. Isopleths for temperature, conductivity and dissolved oxygen

for 1975 and 1976 (Figs. 2a and 2b) show a sequence of generally typical snapshots of water

quality, as do the isopleths of the longitudinal profiles (Figs. 4-10).

3. Surface Processes:

Spring Flood: This is the yearly dominating lake event, dictated by the magnitude and timing

of the spring headwater snow-melt coming down Cataract Canyon and the San Juan River and

into Lake Powell from May to July. These waters are typically fresh (lower conductance/ salinity)

and initiate the warming processes in the lake since the rivers are the first to warm. The spring

freshet may begin injecting at the surface, but the bulk of the flood drops 10 to 20 meters below

the surface of the lake as spring progresses and the lake surface warming exceeds river

temperatures. Though not as warm as the lake's surface, the volume of relatively warm flood

water will dictate the thickness of the epilimnion.

The fresh waters of the typical spring flood reach the dam by July as the last of the snow-melt

enters the reservoir. A small flood moves toward the dam more slowly than a large flood and its

signature may not be seen at the dam before it is dissipated by convective mixing in the fall.

03/06/98

DRAFT

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