GEOMORPHOLOGY 3600 – EXERCISE 2
Comparing Hydrographs Across Utah
OBJECTIVES
 To construct a rating curve relating stream stage to discharge
 To use monthly stream flow and climate data to examine seasonal runoff patterns
 To use daily flow data to construct peak flow event hydrographs
 To relate runoff patterns to the different processes in two Utah catchments
25 points for report that includes 5 plots and answers to the 6 questions.
due Friday, November 6
BACKGROUND
Discharge rating curves:
Stream gauging sites are situated at a point where the channel is stable (i.e. where there is no net
erosion or deposition) so that the discharge can be reliably estimated by recording the height of
the water. River stage, or level, is recorded at regular intervals (usually hourly) at the station.
Direct measurements of discharge are taken at various flows and paired with readings of the
stage, so that a mathematical-graphical relation to discharge can be established. As you know
from lab, direct discharge measurements are time consuming and sometimes dangerous to make.
The automated collection of stage data is much more convenient.
Hydrograph Analysis:
A hydrograph is a plot of discharge or moisture over time. The shape of the hydrograph is
influenced by a number of factors. In addition to overall climate, catchment size, steepness,
vegetation, soil infiltration rates and moisture capacity, annual snow pack, glacier cover,
groundwater conditions, etc. will all affect the overall shape of the annual hydrograph.
Figure 1a shows an example annual hydrograph for Lillooet River, near Pemberton, British
Columbia. The Lillooet River has very rugged headwaters with considerable winter snow
accumulation and a number of glaciers. The Lillooet River has a glacier-dominated regime, since
it has the highest flows in the summer as a result of the gradual melt of first the snowpack and
later of glacier ice. In contrast, rain-dominated regimes exhibit the highest monthly runoff values
whenever frontal or monsoonal weather systems peak in a given landscape. In the example of the
Lillooet, this produces a secondary peak in the fall.
A peak flow hydrograph (Figure 1b) extends from the date at which the flows first begin to
increase to the date that the discharge returns to base flow. The river rises rapidly after runoff
reaches the channel, attaining peak flow some time after the peak of the rainfall itself.
Figure 1c shows the response of a relatively small catchment to daily snowmelt events. Runoff
generated by snowmelt peaks in the late afternoon, and the river swells to peak flows several
hours later. The magnitude of the swells may be greatly augmented by rain-on-snow events. The
peak hydrograph of a river with a snowmelt-dominated regime, like most mountain rivers in
Utah, typically occurs in April or May. Snowmelt hydrographs often have a long, gradual rising
limb and may occur over weeks (Figure 1c).
Figure 1
Catchment Water Balance:
The influence of regional climate (seasonal patterns of temperature and precipitation) on
hydrological processes can be evaluated by comparing the input of water to a catchment as
precipitation to the output as runoff over a given period. Using the concept of mass balance, and
assuming that water is conserved, we know:
input = output + change in storage
-or in this caseprecipitation = evapotranspiration + runoff + storage
Evaporanspiration includes the loss of water to the atmosphere through both direct evaporation
and plant transpiration. Both are most effective when the temperatures are warmer, with the
combined effect strongest during the summer. Runoff includes all the pathways of overland and
subsurface flow discussed in class. The final term, storage, represents changes in the volume of
surface water stored temporarily in lakes and streams, of groundwater, or as snowpack and glacier
ice on the ground surface.
The idea is that seasonal differences between precipitation input and runoff output must be
accounted for by offsetting changes in evapotranspiration or in the amount of water stored in the
catchment.
TO DO: please hand in graphs and typed answers in organized fashion with coverpage that
includes your name and what assignment and class this is. Grammar matters. Figures can be
generated in Excel or other program or hand drawn on the provided graph paper.
For the following questions, perform your analysis on two hydrologic datasets provided from:
A. Blacksmith Fork, northern Utah
B. Upper Paria River, southern Utah
Part I. Constructing and comparing rating curves.
Check out the stage-discharge data for the Blacksmith Fork and Upper Paria rivers (Table A.1
and B.1):
1. On the same Graph 1 (blank provided below), plot the stage-discharge points for both rivers,
using different colors. Plot the discharge (Q) on the Y axis and the stage reading (h) on the X
axis. Note we are using semi-log graph paper, and so the Y axis is logarithmic.
2. Fit a line smoothly between the data points for each river, using different colors or something.
You now have made graphical rating curves, used to determine discharge based on stage.
3. Answer question I.A at end.
Part II. Monthly Runoff and Climate Regimes
Utilize Tables A.2 and B.2 of monthly discharge at the gaging stations, and climate data from a
middle or average location for each drainage basins:
1. Convert the monthly average discharge data in Tables A.2 and B.2 to an equivalent monthly
unit runoff from the catchment (mm of precipitation/per m2of land/per month). READ
CAREFULLY: this is the mean discharge Q [m3/s] multiplied by the # of seconds in the
given month, divided by the total watershed area in [m2]. There are 1,000,000 m2 in a square
kilometer, and the number of seconds in a month depends upon how many days in that
month. To finish the calculation, you need to convert the unit runoff from m to mm (multiply
by 1000). The first three values for the Blacksmith Fork have been done for you so you can
check if you are doing the calculation correctly.
2. For each drainage, plot this annual pattern of runoff using software or on graph paper as a
histogram (bar graph), where the x-axis displays the 12 months of the year in order (January
to December) and the y-axis is the unit runoff in mm/month.
3. Now on your two separate diagrams, graph the appropriate monthly precipitation data listed
in Tables A.2 and B.2. I suggest doing these as line plots right on the same diagrams as the
runoff data. Give a title to your plots, consistent axes, and hand them in with your report.
4. Since precipitation is reported in mm/month, we can directly compare the runoff and
precipitation values over the year. Answer question II.A and B at the end.
Part III. Analysing Peak Discharge Events.
Use the two Excel spreadsheets with discharge data covering the highest annual flows of 2011:
1. In Excel or some other program, for each river, create a line plot with date on the X axis and
discharge on the Y axis. Create systematic vertical and horizontal scales, grids, and labels. In
particular, make both plots with exactly the same vertical scale. Give the plots titles and make
them look good. Hand these in with your report. Note: in the case of the Paria, it will be
easier to make the X axis in hours, not the raw date.
2. Note that the two datasets are of different length. The Blacksmith Fork covers 3 months,
whereas the Paria covers 3 days—yet each covers the peak discharges that occurred on these
rivers in 2011. Answer questions III.A, B, and C at end.
BLACKSMITH FORK
Table A.1:
Stage-discharge relation, 2009 data
Stage (m)
1.19
1.29
1.37
1.44
1.56
1.66
1.81
1.94
2.19
Q (m3/s)
1.76
2.66
3.65
4.53
6.25
8.12
11.49
15.22
24.26
Table A.2: Mean monthly discharge and climate data, 1990-2009
BLACKSMITH FORK GAGE
Latitude: 41°37' N
Longitude: 111°44' W
Catch. area: 681 km2
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Q (m3/s)
1.79
1.90
2.67
4.35
5.08
3.26
2.45
2.17
2.00
1.89
1.78
1.70
Days/month
31
28
31
30
31
30
31
31
30
31
30
31
Q (mm/month)
7.0
6.7
10.5
TEMPLE FORK SNOTEL SITE
Latitude: 41°48' N
Longitude: 111°33' W
Elevation: 2301 m
Precipitation
(mm)
95.3
68.6
69.9
97.8
66.0
87.6
2.5
30.5
10.2
55.9
41.9
87.6
Temperature
(o C)
-4
-5
-0.5
2
4.5
11.5
18
17.5
13.5
5
0
-4.5
UPPER PARIA RIVER
Table B.1:
Stage-discharge relation, 2011 data
Stage (m)
2.08
2.22
2.27
2.36
2.42
2.50
2.68
2.87
3.02
Q (m3/s)
1.26
2.49
3.57
6.03
8.25
11.94
19.75
29.62
39.31
Table B.2: Mean monthly discharge and climate data, 1990-2009
UPPER PARIA GAGE, NEAR HWY 89, UT
Latitude: 37°06' N
Longitude: 111°54' W
Catch. area: 1,676 km2
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
3
Q (m /s)
0.81
0.87
0.87
0.54
0.28
0.14
0.21
0.96
0.26
0.63
0.54
0.42
Days/month
31
28
31
30
31
30
31
31
30
31
30
31
Q (mm/month)
KODACHROME BASIN STATE PK
Latitude: 37°31' N
Longitude: 111°59' W
Elevation: 1833 m
Precipitation
(mm)
29.7
31.0
26.4
17.5
15.2
8.9
25.9
41.1
31.2
32.5
17.5
21.8
Temperature (oC)
-0.7
1.7
5.1
8.9
13.5
18.3
22.1
20.9
16.7
10.3
3.7
-0.7
GRAPH 1: STAGE DISCHARGE RELATIONS
1000.000
DISCHARGE (m3/s)
100.000
10.000
1.000
0.100
0.010
0.000
0.500
1.000
1.500
2.000
2.500
STAGE (m)
3.000
3.500
4.000
4.500
QUESTIONS
ANSWER ALL PARTS OF ALL QUESTIONS. TYPE ANSWERS, DOUBLE SPACED.
I.A. Compare and contrast the shapes of the two curves and think of the geometry of the different
river channels. Which curve is steeper (that is, discharge increases faster with increasing stage),
what might this mean? Which is smoother vs bent? What might a bend in the curve mean?
II.A. For each catchment, describe the patterns between precipitation and runoff, with respect to
their timing and magnitude. Contrast the two --how does the precipitation-runoff relation differ
between them?
II.B. Explain these relations between precipitation and runoff in terms of the factors controlling
the water balance of each catchment. Is storage a significant part of the regime in either? Which
might have more evapotranspiration? How might land use, topography, and bedrock affect these?
III.A. Describe and contrast the two records. When did the peak flow occur in each, and how high
are the peaks? Relative to the background “base” flow, how long did each peak flow event last?
III.B. More specifically, describe the shape and duration of each peak flow hydrograph (e.g.,
steepness of the rising and falling limbs, notable oscillations in discharge during the event, etc.)
III.C. Thinking about hydrologic processes in each of these catchments, hypothesize why their
patterns are different, in terms of climate, vegetation, topography, bedrock, etc. Contrast the
distinct types of hillslope runoff/water pathways probably involved in each catchment.