WSP04101

• File Number: 8080
• Description: Section D General Interstate Litigation - Rainbow Bridge Monitoring Program
• State: CO
• Basin: Statewide
• Date: 5/21/1964
• Author: DOI-BOR
• Title: Rainbow Bridge Monitoring Program - Reports 4 through 10
• Water Supply Pro - Doc Type: Report/Study

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Results of field surveys conducted during this period correlate very
well with past surveys. Results from quadrilaterals designated "A",
"B", and "c" compare favorably with a control quadrilateral, desig-
nated "D". This control quadrilateral was set up 1/2 mile south of
the monument boundary in Bridge Creek Canyon, away from the influence
of the reservoir.

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Quadrilaterals "A" and "B" monitor the foundation of the bridge on
either side. Quadrilateral "c" monitors the top of the bridge struc-
ture and fluctuates with a magnitude slightly greater than that of
"A" and "B". This fluctuation at "C", although somewhat greater in
'magnitude than the other quadrilaterals, maintains a cyclic pattern
and no overall displacement has been discerned.

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In summary, results for this report period correlate with past results
and indicate that Lake Powell has had no short-term adverse effects on
Rainbow Bridge or its foundation.

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2. Rainbow Bridge, Elevation Surveys

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Results from these surveys indicate a close correlation with previous
elevation surveys, and show the same pattern of variations as described
above in the Quadrilateral Surveys section~ As indicated in previous
'reports, these slight changes in elevation of the bridge are directly
related to the change of stress in the bridge caused by seasonal tem-
perature patterns and daily fluctuations cEused by temperature and
other weather conditions. These results ir,dicate no short-term adverse
effects on the Bridge.

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3. Whittemore Strain Gauge Instrumentation

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The Whittemore Gauge records the displacement or movement of selected
cracks at Rainbow Bridge as the cracks respond to the environment and
stress in which they are found.

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The readings obtained during this report period reveal
lation to the data gathered during this time period of

a close corre-
previous years.

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As mentioned in previous status reports, the pattern of contraction
and expansion of the cracks is a cyclical pattern with contraction of
cracks occurring in the summer months and expansion during the winter
months. Current readings support this pattern, with minor deviations
due to the temperature differences at the time the readings were taken.
Daily temperature changes" weather conditions, and exposure time to
the sun all affect the behavior of the cracks, although these daily

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