GEOL_332_lab_04_hand..

advertisement
GEOL 332 Lab 4
Mad River River Bed
Name: _____________________________________________ Date: _______________
Team Name: ___________________________ Team Members: ________________________________
____________________________________________________________________________________
Our goal today is to characterize some fluvial sediments, at two different sites along the Mad River, and
within each site. We will form teams and describe sediments in a few locations. When taking notes of
our observations, we want to take the notes in the same order each time, as usual. We will form groups
of three or four.
We will learn:

How particle size
distributions are
controlled by
geomorphic
setting

How gravel
orientation may
be related to
geomorphic
setting
There will be two stops along
the Mad River. The first stop
will be at the Mad River
pump station park. We will
map the sediment particle
size distribution along a
cross-sectional transect
perpendicular to river flow.
We will prepare a plan view
map and a vertical cross
section. We will collect
Fig. 1. Process domains defined by (a) Schumm (1977) (as depicted by Kondolf, 1994)
and (b) Montgomery (1999).
Wolman Pebble Count
1|P a g e
GEOL 332 Lab 4
Mad River River Bed
Fig. 2. Channel pattern (meandering, straight, and braided) as a function of channel slope and bankfull discharge.
Leopold, L.B., Wolman, M.G. (1957).
Particle size data at
stations based upon an
initial review of the
sedimentary /
geomorphic
environments present.
These data will be
entered into a
spreadsheet and
plotted in various ways.
The second stop will be
along a tributary to the
Mad River, immediately
upstream of its
Fig. 3. Schumm’s (1963a, 1977, 1981, 1985) classification of alluvial rivers.
confluence with the Mad
2|P a g e
GEOL 332 Lab 4
Mad River River Bed
River. We will also prepare a plan
view map, vertical cross section,
and particle size data. We will
supplement these data with a
sediment clast imbrication analysis.
The particle size data will be
plotted like for stop 1. The clast
imbrication data will be plotted on
a stereo net, using poles to planes
and plunge axis plots. This may be
done by hand or with software.
Sedimentary Environments
Fluvial sedimentary environments
can be spatially related to different
fluvial geomorphic processes.
When interpreting fluvial
sediments and rocks, having a
knowledge about what particle size
distributions occur in different
geomorphic settings improves the
likelihood that one’s interpretation
is correct. To do this, we must
know a little about fluvial processes
and different geomorphic settings.
One way to approach this is to
consider geomorphology, which
implies that “form implies
process.”
There are many uses for channel
classification systems (simplifying
Fig. 4. Schumm’s (1977, 1981, 1985) classification of channel pattern and
response potential as modified by Church (2006).
complex models for interpreting the complex continuum of processes and conditions within a landscape
3|P a g e
GEOL 332 Lab 4
Mad River River Bed
by identifying places that
function in a similar
manner, interpreting and
assessing entrainment,
transport, and
depositional conditions,
etc.). We will use some of
these classification
systems to help us
visualize the variation in
fluvial sedimentary
environments.
Process Domains:
Schumm (1977) divided
rivers into sediment
production, transfer, and
deposition zones, providing a
process-based view of
sediment movement through
river networks over geologic
time (Figure 1A).
Process domains are portions
Figure 5. Map and diagrammatic schematic views of a drainage basin to illustrate the
concept of ‘coupling’ between a stream channel and adjacent hillside slopes. Near the
upstream limit of the decoupled reach there will usually be a significant ‘partially coupled’
reach, where stream channels move against, and then away from adjacent hillslopes. On the
left side of the diagram are schematic graphs of characteristic grain size distributions
through the channel system. In each graph, the next upstream distribution is shown (dashed
line) so the intervening modification by stream sorting processes may be directly appraised.
On the right hand side of the diagram are graphs to illustrate the attenuation of sediment
movement down the system. Attenuation is the consequence of increasing mobility of finer
material farther downstream, tributary confluences with variations in runoff timing, and of
diffusive processes associated with channel flow.
of the river network characterized by specific suites of interrelated disturbance processes, channel
morphologies, and aquatic habitats, and at a general level roughly correspond with source, transport,
and response reaches in mountain basins (Figure 1B; Montgomery, 1999).
Classification of rivers using process domains is a coarse filter (typically lumping several channel types),
but it identifies fundamental geomorphic units within the landscape that structure general river
behavior and associated aquatic habitats.
Channel Pattern: Most river classifications that have been developed involve classification of channel
pattern (i.e., planform geometry, such as straight, meandering, or braided), which can be broadly
4|P a g e
GEOL 332 Lab 4
Mad River River Bed
divided into two approaches: (1) quantitative relationships
(which may be either empirical or theoretical) and (2)
conceptual frameworks.
Quantitative relationships – Lane (1957) and Leopold and
Wolman (1957) observed that for a given discharge, braided
channels occur on steeper slopes than meandering rivers
(Figure 2).
Conceptual frameworks – Schumm’s (1960, 1963, 1968,
1971a, b, 1977) work on sand- and gravel-bed rivers in the
Great Plains of the western U.S. emphasized that channel
pattern and stability are strongly influenced by the imposed
load of the river (size of sediment and mode of transport)
and the silt-clay content of the floodplain (providing
cohesion necessary for the development of river
meandering). Based on these observations, Schumm (1963,
1977, 1981, 1985) proposed a conceptual framework for
classifying alluvial rivers that related channel pattern and
stability to (1) the silt-clay content of the banks, (2) the
mode of sediment transport (suspended load, mixed load,
bed load), (3) the ratio of bed load to total load (a function
of stream power, sediment size, and supply), and (4) the
Channel elements in high gradient
channels (a) step-pool system; (b)
pool-riffle-bar system.
slope and width-to-depth ratio of the channel (Figure 3).
Schumm’s (1963a, 1977, 1981, 1985) classification has since been refined to include a broader range of
channel types (Mollard, 1973; Brice, 1982), including steeper morphologies present in mountain rivers
(Church, 1992, 2006; Figure 4).
Channel pattern classification approaches are typically descriptive (associating physical conditions with
channel morphology, but not explaining the underlying processes) or involve a mixture of descriptive
and process-based interpretations. A comprehensive presentation of different channel classification
systems is in Buffington and Montgomery (2013).
5|P a g e
GEOL 332 Lab 4
Mad River River Bed
Church (2002) presented a
figure that shows how sediment
size may vary in a drainage
basin, a conceptual approach
listed above (Figure 5). Church
(2002) also presents a figure
that shows how particle size
may vary in different
sedimentary settings (Figure 6).
Bunte and Abt (2001) present a
schematic longitudinal and
planform view of five stream
types at low flow. (A) Cascade
with nearly continuous highly
turbulent flow around large
particles; (B) Step-pool channel
with sequential highly turbulent
flow over steps and more
tranquil flows through
intervening pools; (C) Plane-bed
channel with an isolated boulder
protruding through otherwise
uniform flow; (D) Pool-riffle
channel with exposed bars,
highly turbulent flow over riffles,
and more tranquil flow through
pools; and (E) Dune-ripple
Fig. 7. Schematic longitudinal (left) and planform (right) illustration of
the five stream types at low flow: (A) Cascade with nearly continuous
highly turbulent flow around large particles; (B) Step-pool channel with
sequential highly turbulent flow over steps and more tranquil flows
through intervening pools; (C) Plane-bed channel with an isolated
boulder protruding through otherwise uniform flow; (D) Pool-riffle
channel with exposed bars, highly turbulent flow over riffles, and more
tranquil flow through pools; and (E) Dune-ripple channel with duneripple bedforms.
channel with dune-ripple
bedforms (Figure 7).
Finally, Rosgen (1994) relates stream form to slope, cross section, plan view, and particle size (Figure 8).
6|P a g e
GEOL 332 Lab 4
Mad River River Bed
An illustration that attempts to
bring together the major
factors that control
entrainment, transport, and
deposition in a fluvial system is
presented in Figure 9. In the
Lane balance diagram, flow–
sediment interactions
determine the aggradational –
degradational balance of river
courses. (a) The river maintains
a balance, accommodating
adjustments to the
flow/sediment load. (b) Excess
flow over steep slopes, or
reduced sediment loads, tilts
the balance towards
degradation and incision
occurs. (c) Excess sediment
loads of a sufficiently coarse
nature, or reduced flows, tilt
the balance towards
aggradation and deposition
Fig. 8. Rosgen’s stream classification. Longitudinal, cross-sectional and plan views of
mayor stream types (top); Cross-sectional shape, bed-material size, and morphometric
delineative criteria of the 41 major stream types (bottom).
occurs. The arrows on (b) and
(c) indicate the way in which the channel adjusts its flow/sediment regime to maintain a balance.
Wolman Pebble Count
The composition of the streambed and banks are important facets of stream character, influencing
channel form and hydraulics, erosion rates, sediment supply, and other parameters. Observations tell us
that steep mountain streams with beds of boulders and cobbles act differently from low- gradient
streams with beds of sand or silt. You can document this difference by collecting representative samples
of the bed materials using a procedure called a pebble count. In this case, one would collect particle size
7|P a g e
GEOL 332 Lab 4
Mad River River Bed
Fig. 9. The Lane balance diagram. Flow–sediment
interactions determine the aggradational –
degradational balance of river courses. (a) The river
maintains a balance, accommodating adjustments to
the flow/sediment load. (b) Excess flow over steep
slopes, or reduced sediment loads, tilts the balance
towards degradation and incision occurs. (c) Excess
sediment loads of a sufficiently coarse nature, or
reduced flows, tilt the balance towards aggradation and
deposition occurs. The arrows on (b) and (c) indicate the
way in which the channel adjusts its flow/sediment
regime to maintain a balance. Modified from Lane
(1955).
data across the entire fluvial landscape within
the reach of river or stream, using the “zigzag” data collection pattern (Bevenger and
King, 1995). Alternately, one could analyze
different geomorphic settings within a reach
of a river or stream. In this case, one would
limit their station analyses to those specific
geomorphic settings. We will be analyzing
Fig. 10. Clast axes: (A) Long Axis, (B) Intermediate Axis, and (C)
Short Axis.
specific geomorphic settings at our first stop and a hybrid approach at our second stop.
Regardless of which method one uses, for each data collection station, the following are the general
steps. “Averting your gaze,” pick up the first particle touched by the tip of your index finger at the toe of
your shoe/boot/wader. Measure the intermediate axis (neither the longest nor shortest of the three
8|P a g e
GEOL 332 Lab 4
Mad River River Bed
mutually perpendicular sides of each particle picked up;
Table 1. Clast Site Classes
Axis B; Figure 10). Measure embedded particles or those
too large to be moved in place. For these, measure the
smaller of the two exposed axes. Call out the
measurement. The note taker tallies it by size class and
repeats it back for confirmation. There are many
different size class schema. For this lab, use the size
classes presented in Table 1.
Clast Orientation
Clast imbrication is an indicator of modern current and
palaeocurrent direction. There are many aspects that are
important to consider and these are detailed in Bunte and Abt (2001).
For our data collection in this lab, we
will collect the strike and dip for a
number of clasts at stop 2 of our field
trip (Figure 11). For clasts that have
equal B- and C-axis measurements (a
“roller”), collect the data as trend
(compass orientation; the same as
strike) and plunge (angle below the
horizontal plane; Figure 12).
Many people use a small sheet of
Fig. 11. Strike and Dip. From Dr. M.H. Hill at Jacksonville State University here:
http://www.jsu.edu/dept/geography/mhill/phylabtwo/lab4/dipf.html
rigid aluminum to help determine the orientation of the clasts that one is measuring. The instructor will
have small pieces of cardboard for those without a sheet of aluminum. Basically, hold the card
(aluminum or cardboard) with the flat dimensions of the card aligned with the A-B axis direction. Then
use one’s pocket transit to measure the strike and dip of the orientation of the card. Have one person
make observations, one person collect the data, and the third person locate the station on the map and
the cross section. Rotate these roles during the cross-section transect.
9|P a g e
GEOL 332 Lab 4
Mad River River Bed
Stop 1: Mad River at the pump
station park
Here we will conduct our first sediment
sampling transect. We will conduct a
single river flow perpendicular crosssection transect along the river,
perpendicular to the flow. The crosssection transect will extend from the
wetted edge, southward, across the
gravel bar, and up to the edge of the
vegetated floodplain. Take a look at the
cross-section transect and think about
the different sedimentary
environments along the cross-
Fig. 12. Orientation and Plunge. From: http://www4.ncsu.edu/~fodor/mea101.html
section transect. Choose three
pebble count stations. We will conduct a Wolman Pebble Count at stations in each of these sedimentary
environments. One person should make the observation and the other two should take notes. Rotate
these roles during the lab, at each of the three stations. Make sure that everyone has a full set of these
data observations in their own notebooks. This might involve making electronic scans of your notebooks
after the field trips is over (to save time).
Prepare a plan view and cross sectional view of your cross section transect. Distances will be based upon
your paces and the vertical changes in elevation will be estimated. Make sure that your group’s maps
and cross sections generally match. Label your stations on the map and the topographic cross section.
You will include these illustrations in your report.
Pebble count data will be entered into an electronic spreadsheet. Prepare two plots: (1) a volume
percent frequency distribution and (2) a cumulative percent distribution. Plot each sample location with
a different symbol.
Stop 2: Mad River upstream of the Blue Lake Bridge
Here we will conduct our second sediment sampling transect. We will conduct a single transect along
this tributary to the Mad River, Just upstream of the confluence. Each team will prepare a topographical
10 | P a g e
GEOL 332 Lab 4
Mad River River Bed
cross section, using a stadia rod and pocket transits. Each team will sample the particle size distribution
at evenly spaced stations across the river flow perpendicular cross-section transect. Finally, each team
will collect clast imbrication data for about 10 clasts in each sedimentary environment. We will set up
the cross section transects at one river mile position, and collect clast orientation data upstream of the
cross section transect.
Report
Meet with your group sometime after the field trip is over. Discuss your observations in the field, the
data, the results, and what you learned during and after the field trip. You might want to meet twice,
before you do your analyses and after you perform your analyses. If you work together, feel free to
share the same spreadsheet within your group (the data entry is time consuming). I would like each
student to prepare their own plots.
Prepare a report and submit electronically to [email protected] . This lab is due prior to class
two weeks from the day of the field trip. I will not accept hard copies of your report.
The filename needs to be in the correct format or you will miss out on some points!!! The name format
is in the syllabus.
The report should be in a standard format (e.g. introduction, methods, results, discussion, and
conclusion). I have placed a writing guide on the website. The report should include tables of your data,
your maps, and your cross sections. Each table, map, and cross section needs to have a figure caption.
References:
Bevenger, Gregory S.; King, Rudy M., 1995. A pebble count procedure for assessing watershed cumulative effects. Res. Pap. RMRP-319. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station.
17 p.
Brice, J.C., 1982. Stream channel stability assessment. US Department of Transportation, Federal Highway Administration
Report FHWA/RD-82/021, Washington, DC, 42 pp.
Buffington, J.M., Montgomery, D.R., 2013. Geomorphic classification of rivers. In: Schroder, J. (Editor in Chief), Wohl, E. (Ed.),
Treatise on Geomorphology. Academic Press, San Diego, CA, vol. 9, Fluvial Geomorphology, p. 730–767.
Bunte, K. and Abt, S. R. 2001. Sampling surface and subsurface particle-size distributions in wadable gravel- and cobble-bed
streams for analyses in sediment transport, hydraulics, and streambed monitoring. Gen. Tech. Rep. RMRS-GTR-74. Fort Collins,
CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 428 p.
Church, M., 1992. Channel morphology and typology. In: Carlow, P., Petts, G.E. (Eds.), The Rivers Handbook. Blackwell, Oxford,
UK, pp. 126–143.
Church, M., 2002. Geomorphic thresholds in riverine landscapes. Freshwater Biology 47, p. 541–557.
Church, M., 2006. Bed material transport and the morphology of alluvial rivers. Annual Review of Earth and Planetary Sciences
34, p. 325–354.
11 | P a g e
GEOL 332 Lab 4
Mad River River Bed
Kondolf, G.M., 1994. Geomorphic and environmental effects of instream gravel mining. Landscape and Urban Planning 28, p.
225–243.
Lane, E. W., 1955. The importance of fluvial morphology in hydraulic engineering. Proceedings, American Society of Civil
Engineers, v. 81, Paper 745, pp. 17.
Lane, E.W., 1957. A study of the shape of channels formed by natural streams flowing in erodible material. U.S. Army Engineer
Division, Missouri River, Corps of Engineers, MRD Sediment Series no. 9, Omaha, NE, 106 pp.
Leopold, L.B., Wolman, M.G., 1957. River channel patterns: braided, meandering, and straight. U.S. Geological Survey
Professional Paper 282-B, Washington, DC, p. 39–84.
Mollard, J.D., 1973. Air photo interpretation of fluvial features. Fluvial Processes and Sedimentation. National Research Council
of Canada, Ottawa, ON, p. 341–380.
Montgomery, D.R., 1999. Process domains and the river continuum. Journal of the American Water Resources Association 35,
p. 397–410.
Rosgen, D.L., 1994. A classification of natural rivers. Catena 21: 169-199.
Schumm, S.A., 1960. The shape of alluvial channels in relation to sediment type. U.S. Geological Survey Professional Paper 352B, Washington, DC, pp. 17–30.
Schumm, S.A., 1963. A Tentative Classification of Alluvial River Channels. U.S. Geological Survey Circular 477, Washington, DC,
10 pp.
Schumm, S.A., 1968. Speculations concerning paleohydrologic controls of terrestrial sedimentation. Geological Society of
America Bulletin 79, p. 1573–1588.
Schumm, S.A., 1971a. Fluvial geomorphology: channel adjustment and river metamorphosis. In: Shen, H.W. (Ed.), River
Mechanics. H.W. Shen, Fort Collins, CO, p. 5-1–5-22.
Schumm, S.A., 1971b. Fluvial geomorphology: the historical perspective. In: Shen, H.W. (Ed.), River Mechanics. H.W. Shen, Fort
Collins, CO, pp. 4-1–4-29. Schumm, S.A., 1977. The Fluvial System. Blackburn Press, Caldwell, NJ, 338 pp.
Schumm, S.A., 1981. Evolution and response of the fluvial system, sedimentological implications. In: Ethridge, F.G., Flores, R.M.
(Eds.), Recent and Nonmarine Depositional Environments. SEPM (Society for Sedimentary Geology), Special Publication 31,
Tulsa, OK, p. 19–29.
Schumm, S.A., 1985. Patterns of alluvial rivers. Annual Review of Earth and Planetary Sciences 13, p. 5–27.
12 | P a g e
Download
Related flashcards
Languages of Oman

16 Cards

Navigation

27 Cards

Create flashcards