Dames & Moore, 1999 - USDA Forest Service

The data logger, or transducer, was placed in the pool behind the weir and measures water level. A rating
curve was developed to allow discharge flow rates to be determined based on the height of water measured
behind the weir with the transducer.
Referring to Figure 4.3-7% transducer output for the period from early October to late December 1997 was
very erratic. The erratic nature of the data may have been the result of freezing temperatures, which would
likely have caused ice build-up in the V-shaped notch in the weir. The ice buildup could have restricted
water flow through the V-shaped notch, resulting in increased water levels behind the weir. As the water
levels continued to increase, the water would eventually overtop the ice, resulting in melting and a decrease
in the pool level. This phenomenon could have been cyclical, which would explain the plotted data on
Figure 4.3-7a.
Based on the precipitation data presented in Table 4.3-2, the months of highest precipitation at Holden
Village are October through March. Referring to Table 4.3-3, the average temperatures between November
and February are below O°C (32°F). Therefore, the precipitation would fall in the form of snow.
As snow continued to accumulate through the months of November and December, the portal opening
would eventually be filled with snow. The snow would insulate the portal, thereby reducing the likelihood
of freezing. Referring to Figure 4.3-7a, the transducer data output after December becomes less erratic.
Another possible explanation for the erratic data during the period between October and December may be
the impact of freezing temperatures on the operation of the transducer. Due to relatively low water levels
during this period of time, the majority of the transducer would not be in the water, making it susceptible to
freezing. Assuming that the portal opening becomes blocked with snow after ~ecember, as speculated
above, the insulating conditions would reduce the likelihood of freezing conditions, and the transducer
would function normally.
It is also possible that the erratic behavior depicted on Figure 4.3-7a from early October to late December is
the result of a combination of the above-mentioned phenomena. As noted on Figure 4.3-7% the discharge
rate of the portal drainage was observed to be relatively constant from early January 1998 to late April 1998,
and then climbed from approximately 0.05 cfs to approximately 1.80 cfs within approximately one to two
days. Between late April to early June 1998, the discharge rates fluctuated between approximately 0.70 cfs
to 1.70 cfs. However, the data record was interrupted for six days in May 1998 when the plastic lining
placed on the upstream side of the weir failed, resulting in loss of water. The weir was repaired and the
transducer reinstalled on May 7, 1998. Figure 4.3-7b is a graphical representation of portal drainage
discharge and precipitation data collected at Holden Village in 1998. Precipitation data were not available
for Holden Village for October 1997 through early May 1998 in order to allow a comparison of transducer
data for that period of time. However, the comparison of precipitation and transducer data for the period
between early May and mid-October 1998 indicate the following:
For the period of time between early May and midJune 1998, the portal drainage
responded within approximately one day of precipitation events with discharge rate
increases as high as 100 percent when compared to the pre-precipitation event conditions.
The flow increases were short-lived and the discharge rate returned to pre-precipitation
event conditions within approximately one day.
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17693-005-019Vuly 19. 1999;4:1(1 PM:DRAFT FINAL RI REPORT