WSP04999

• File Number: 8054
• Description: Water Salvage
• State: CO
• Basin: Statewide
• Date: 6/1/1975
• Author: Utah Water Research
• Title: Water Salvage Potentials in Utah - Volume II - Evaporation Suppression by Reservoir Destratification
• Water Supply Pro - Doc Type: Report/Study

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SUPPRESSION WITH COOLED EV APORA TION PANS

Use of historic enporadOD data

One possible source of verification for the
suppression/temperature function in the model
which was investigated during the initial phase of
this research was the analysis of historic Utah pan
evaporation data. The approach was to divide the
daily dala into several discrete categories. each of
which had nearly equal wind measurements. The
data used included daily evaporation. maximum
and minimum air temperature. and daily total
wind.

The intent was to eliminate wind as a variable
by segregating the data according to wind (5 mph
increments). However. since humidity measure.
roents were not available. there was no way of
eliminating humidity as a variable. Regression
analysis of the data produced very poor correlation.
The correlation between evaporation and average
air temperature yeilded R' values as high as .80 on
two wind categories but most RZ values wefe less
than .60.

The possible reasons for the large amount of
noise in the data are numerous. They include:

J. Ignoring differences in humidity of the

air.

2. Using air temperatures instead of water
temperatures for daily data.

3. Measurement and other errors inherent in
pan operations.

The inadequate results of this attempt to use
existing climatological data to verify the model
clearly demonstrated the need for a controlled
evaporation experiment during which evaporation
is measured simultaneously at pans which have
different water temperatures but with other
parameters such as wind and humidity being
identical. The balance of this section is devoted to
such an experiment.

Experiment design

In order to empirically determine evaporation
change as a function of water temperature change
only. the experiment was designed with evapora-
tion pans at different water temperatures but at the
same location so that identical wind and humidity
conditions were acting upon each pan. Three
evaporation pans were used at the station; two of
the pans were cooled by running water through
coils beneath the water surface. The third pan
had no temperature control; it was a normal
evaporation pan serving as a standard reference.
Air and water temperatures, dew point, precipita-
tion and wind were all recorded. Temperature and
dew point readings were recorded every 20 minutes.
Total wind. precipitation and evaporation were
recorded once a day. This phase of the research is
described in detail in an M.S. Thesis by James
Frankiewicz (1975) which is summarized here.

EnporadoD pans

General: The evaporation pans were con-
structed according to U.S. Weather Bureau Class
"A" pan specifications. Two pans were then fitted
with a concentric spiral shaped from I-inch
diameter aluminum tubing. The spiral. situated
approximately 2 inches up from the bottom. circled
from the pan edge into the center. The tubing was
connected to hose couplings mounted through the
sides of the pan.

Pan cooUog: The municipal water system
supplied a steady flow of constant temperature
water at approximately 9.50C for cooling the north
and center pans. The water was transported to the
pans through an insulated hose. Gate valves were
installed on the pan inlet couplings; the valves were
used to regulate the flow through the tubing and
the resultant cooling of the pans. A high flow rate
was maintained through the coils in the center pan
and a lower flow rate was used in the north pan.
The cooling water was taken from a connection on
the opposite side of the pan and into a nearby
drain.

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