Fluvial Geomorphology Geol/WatS 5150/6150
Test 1
You have until 1:15p to complete this test. You may use your notes and your lecture
notes. You may use spreadsheets that you have been provided in class.
Graduate students are to answer all questions. Undergraduate students are to answer
questions 1-4, 6-7, 9.
Show all work.
Hydrology:
1) Graph (A) is a flow duration curve of the Colorado River at Lees Ferry, Arizona
(USGS station 09380000). Graph B is a probability distribution of the daily range of
discharge, meaning the difference between the largest and smallest instantaneous
discharge on each day. Graph C is a flood frequency plot. The legend for graph C is
included immediately below the graphs.
Based on these three graphs, describe the ways in which operations of Glen
Canyon Dam have changed the flow regime of the Colorado River downstream
from the dam.
Source for graphs:
Topping et al., 2003, US Geological Survey Professional Paper 1677.
Graph A.
Graph B.
Graph C.
Sediment Supply and sediment yield
2) Figure 1 shows a sediment budget for the Minnesota River for the Holocene
(~10,000 years ago to modern times), and for years 2000 – 2010. Look at the
magnitude of changes in the source areas of sediment. What are the largest source
areas of sediment for the modern period? How much more sediment is being
deposited on the floodplains, and how much more sediment is being exported from
the basin between 2000-2010 compared to the Holocene. Why have such dramatic
changes occurred?
Figure 1.
Hydraulics
3) When making a discharge measurement, the average velocity of the cross-section
is equal to the average of all the individual measurements of velocity that are made.
True or false? Justify your answer.
4) We often speak of the average boundary shear stress in steady, uniform flow as
the “depth-slope product.” What is the basis for this approximation?
5) Is the extra shear stress induced by generation of a diurnal wave caused by
production of hydroelectric power ranging from 8000 ft3/s to 25,000 ft3/s over a 3-
hr period a significant addition to the sediment transport capacity of the Colorado
River in Grand Canyon when compared to the shear stress caused by a steady
discharge of 8800 ft3/s? For the sake of this question, assume that the channel is
rectangular in form with an average width of 86 m, that the average slope is 0.0014,
and the roughness of the channel is 0.035. The length of channel over which this
increase in flow occurs should be calculated as the mean flow velocity of the high
flow times the duration of rise in flow.
6) What proportion of the total boundary shear stress of Redwood Creek, near Napa,
CA, acts on the individual grains and therefore is the best predictor of sediment
transport?
R ~ 3.0 ft (at bankfull)
width = 62 ft (at bankfull)
slope = 0.0096
velocity = 6.2 ft/sec (at bankfull)
D50 = 90 mm
D65 = 110 mm
D84 = 140 mm
Sediment transport concepts
7) Explain the concepts of selective entrainment and equal mobility and how these
concepts differ in explaining when bed grains begin to be transported by stream
flow. Develop your answer in terms of the basic equation that defines bed
entrainment.
8) A boulder 360 mm in b-axis diameter sits in the middle of the Blacksmith Fork.
What is the approximate likelihood that this boulder moves? (D50 = 80 mm; channel
slope is 0.010, assume the critical Shield’s number is 0.045).
This graph shows the annual instantaneous peak discharge of the stream.
This graph shows the mean flow depth (in feet) as a function of discharge (in cubic
feet per second) for all measurements made since November 2008.
7
6
5
4
Series1
3
2
1
0
0
500
1000
1500
9) In the Meyer-Peter and Mueller transport equation
q* = 8(t * -t c *)1.5
grain size is not a variable in this equation. So … why do we measure grain size of
the bed when we want to predict bed material transport? How does grain size affect
a sediment transport calculation?