WSP09785

• File Number: 8142.600.30.A
• Description: Trinidad Project - Studies - Other Studies - Purgatoire river transit loss study
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 1/1/1993
• Author: USGS
• Title: Evaluation of Streamflow Traveltime and Streamflow Gains and Losses Along the Lower Purgatoire River Southeastern Colorado 1984-1992
• Water Supply Pro - Doc Type: Report/Study

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D DAILY ANALYSIS
. STREAMFLOW.EVENT
o ANALYSIS

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NOTE: NOT ALL OUTLIERS ARE SHOWN

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WINTER

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Figure 10. Boxplots showing daily mean streamflow gains and losses and daily mean streamflow-event gains and losses
for reach 2 of. the study area, 1984-92.

The statistical summary of daily estimates for
reach 3 (table 3) indicated that median streamflow
gain was at least 2 ft3ts during all four seasons.
During winter, gain-and-loss computations were made
for 812 days, resulting in a daily median gain of
2 ft3ts; during spring, gain-and-loss computations
made for 828 days had a daily median gain of 8.7 ft3ts;
during summer, gain-and-loss computations made for
828 days had a daily median gain of 16 ft3ts; and
during fall, gain-and-loss computations made for
819 days had a daily median gain of 12 ft3ts (table 3).
Statistical analysis, using a one-tailed t-test (Iman and
Conover, 1983), was used to assess if daily streamflow
gains were significantly greater than zero during some
seasons. A one-tailed hypothesis test assumes that the
difference is greater than zero. Results of the test
using the 1984-92 estimated gain-and-loss data
indicated that during all four seasons, the daily gains
of streamflow in reach 3 were significantly different
from zero at the 95-percent confidence level.
In addition to the more than 3,200 daily
computations of streamflow gains and losses in
reach 3, boxplots are shown in figure 11 that
summarize streamflow gain-and-loss calculations

for 88 selected streamflow events between 1984
and 1992. Gain-and-loss computations for 3 winter
streamflow events that were analyzed had a daily
median gain of 2 ft3ts; for 19 spring streamflow
events, a daily median gain of 7 ft3ts; for 57 summer
streamflow events, a daily median gain of 15 ft3ts; and
for 9 fall streamflow events, a daily median gain of
4 ft3ts (table 3). The streamflow-event estimates in
reach 3 ranged from a daily gain of 275 ft3ts to a daily
loss of 224 ft3ts (table 3).
The daily occurrence of streamflow gains in
reach 3 could be because of ground-water inflows and
. other ungaged streamflows that might occur in an
irrigated river reach; the sources likely are from field
; tailwater, canal operations, and other ungaged surface-
. water sources. No records of tributary inflow were
available for reach 3. Ungaged tributary inflow into
reach 3 was assumed to be small. During those days
; when side-channel inflows from ungaged tributary
streams were large, gain-and-Ioss computations
indicated a large daily gain; these large reported
streamflow gains were outlier values in the gain-and-
loss boxplots (fig. 11).

20 Evaluation of Straamflow Travaltlme and Streamflow Galne a~d Losaea along the Lower Purgatoire River,
Southeastern Colorado, 1984-92