Appendix 61
USGS Gaging Station Hydrologic Data
This appendix summarizes hydrologic data from USGS gaguing stations. To view a file, click on one the
following links:
Flathead Lake
Flathead River at Columbia Falls
Flathead River Perma
Flathead River Polson
Hungry Horse Res.
Mid. Frk Flathead R.
N. Frk Flathead R.
S. Frk Flathead R.
Stillwater River
Swan River
Whitefish River
Each of the files include the following sheets or pages that can be viewed by clicking on the tabs at the
bottom of each page within the file:
1. Read Me
A cover page describing the contents of the file.
2. Daily Flow Values
Mean daily discharge values for period of record.
3. Comparative Hydrograph Chart(s)
Annual hydrograph for minimum annual volume, maximum annual volume, and near average
volume flow. For an explantion, see page 2 of this document.
4. Comparative Hydrograph Data
Mean daily flow values used to prepare Comparative Hydrograph Chart(s).
5. Duration Data Chart
Flow duration chart based on mean daily discharge. For an explanation of how to read this chart,
see page 3 of this document.
6. Duration Data Compare
Mean daily discharge exceedence values used to prepare the Duration Data Chart.
7. Peak Flow Values Chart
Annual instantaneous peak flood flow series. For an explanation of this chart, see page 4 of this document.
8. Peak Flow Values
Instantaneous peak flood flow series for period of record.
A brief primer on how to read the charts within each file follows.
Comparative Hydrograph Charts
These charts show how the hydrograph of the river changes seasonally and as a result of regulation
(when a river is regulated by a dam more than one chart will be included). In this file, the top chart
shows the hydrograph of the South Fork of the Flathead River before Hungry Horse Dam started
regulating the river. The three lines represent the river at three different years (minimum yield
year, near average yield year, and maximum yield year). The bottom chart shows the hydrograph of
the river with regulation by Hungry Horse.
Comparative Flow Hydrograph: South Fork Flathead River near Columbia Falls (12362500)
Period: 1929-1951, pre Hungry Horse Regulation
1941 minimum yield, 1933 near average yield, 1935 maximum yield
40000
mean daily discharge (cubic feet per second)
35000
30000
25000
20000
15000
10000
5000
16-Sep
16-Sep
30-Sep
2-Sep
5-Aug
19-Aug
8-Jul
22-Jul
24-Jun
10-Jun
27-May
29-Apr
13-May
15-Apr
1933
2-Sep
1941
1-Apr
4-Mar
18-Mar
4-Feb
18-Feb
21-Jan
7-Jan
24-Dec
10-Dec
26-Nov
12-Nov
29-Oct
1-Oct
15-Oct
0
1935
Comparative Flow Hydrograph: South Fork Flathead River near Columbia Falls (12362500)
Period: 1952-2001, Hungry Horse Dam complete
1953 minimum yield, 1983 near average yield, 1996 maximum yield
18000
14000
12000
10000
8000
6000
4000
2000
1983
1996
30-Sep
5-Aug
19-Aug
22-Jul
8-Jul
24-Jun
10-Jun
27-May
13-May
29-Apr
15-Apr
1-Apr
4-Mar
1953
18-Mar
18-Feb
4-Feb
21-Jan
7-Jan
24-Dec
10-Dec
26-Nov
12-Nov
29-Oct
1-Oct
0
15-Oct
mean daily discharge (cubic feet per second)
16000
Duration Data Chart
This chart tells the viewer the percentage of the time that a given daily discharge was equaled or
exceeded. There will be two lines on the chart if the river is regulated, which allows one to compare
pre-dam conditions with post-dam conditions. On this chart for the South Fork of the Flathead at
Columbia Falls, it shows comparative flow duration curves for the priod before Hungry Horse (blue
line) and after Hungry Horse (magenta line).
Comparative Flow Duration Curve:
South Fork Flathead River near Columbia Falls (12362500)
period 1911-1951, pre-Hungry Horse Dam and
1952-2001, post Hungry Horse Dam
mean
dailydischarge
discharge (cubic
perper
second)
mean
daily
(cubicfeet
feet
second)
100000
Prior to the construction
of Hungry Horse, 10,000
cfs was equaled or
exceeded 12% of the
time (about 44 days out
of the year).
10000
After the construction
of Hungry Horse,
10,000 cfs was equaled
or exceeded only 4%
of the time (about 15
days out of the year).
1000
100
0
10
20
30
40
50
60
70
percent of time discharge was equaled or exceeded
pre Hungry Horse
post Hungry Horse
80
90
100
Peak Flow Values Chart
This chart shows the viewer the annual peak flow for each year for the period of record. The red
vertical line marks the year that regulation on a river started, which allows one to see the impact of
regulation on peak flows. This chart is for the South Fork of the Flathead River at Columbia Falls. In
1952, Hungry Horse Dam began regulating the river, and the chart shows the sharp reduction in
annual peak flows brought about by the dam.
Annual Peak Flow Flood Series:
South Fork Flathead River near Columbia Falls (12362500)
Period: 1911 through 2001
50000
Hungry Horse regulation
45000
annual peak flood flow value (cfs)
40000
35000
30000
25000
20000
15000
10000
5000
0
1911
1921
1931
1941
1951
1961
water year
1971
1981
1991
2001