1. Fluvial Geomorphology
ESS 400a
Summer 2017
Lecture for Thursday morning, 7/30/2015
Before we start mapping the site, lets have a crash course in fluvial geomorphology and hopefully some of the observations you’ll make will click!

2. The fluvial system Headwaters Straight channel Tributary
Meandering channel
Delta
Rivers are conduits for water and sediment, and they are also geomorphic agents.
They affect and are affected by their surrounding landscape.
Let’s start with a drawn out look at the whole of the fluvial system – from headwaters to mouth.
Channels start in steeper highlands and water flows down the system. As it does so, the morphology of the channel changes. We start in the headwaters with straight channels, then progress to meandering (maybe some braided), and then to a delta. What is driving all the water flow?
Water flow

3. The fluvial system Gravity! The engine for geomorphic work Headwaters
Straight channel
Tributary
Meandering channel
Delta
Gravity! The fluvial system and its geomorphic components are all driven by gravity, which determines how much energy is available to do work.
Water flow

4. The fluvial system
Gravity drives changes….but the amount of water and sediment is controlled by basin size.
Drainage basin (watershed): the area contributing water and sediment to the channel
While gravity has a large influence on driving changes, the amount of water available to make those changes is also important. One way of thinking of how much water a system has is by considering its drainage basin or watershed size. A watershed is the area contributing water and sediment into a channel, and its divides are often high ridges.
Hillslope processes going on in the drainage basin also control how much sediment is supplied to the watershed.

5. The fluvial system
The volume of water increases downstream as more tributaries and run-off join
This volume of water is termed discharge, and is the volume of water flowing through a channel per time unit
Therefore, Q = v * A
So as Q increases, velocity and area increase
However, one thing to think of for our purposes is that discharge is pretty constant at the reach scale, where no tributaries (or irrigation channels) take water in or out of the system. So in our study area, Q should be constant, so v*A will balance each other out. Does this makes sense – low velocity areas are pools, which are deeper, so have higher A’s to make up for lower v.
Note: At the reach scale, such as Price Creek, Q is constant

6. Hydrology Q = area * velocity = width * depth * velocity
As we discussed earlier, discharge is the cross sectional area times the flow velocity, which is equivalent to the width times the depth times the velocity. That assumes a rectangular channel.

7. The fluvial system Straight channels: What do these streams look like?
We also classify channels based on their shape. First, we have straight channels, which tend to form in the mountainous headwaters.

8. The fluvial system Meandering channels:
What do these streams look like?
Meandering channels:
In the lowlands, we have meandering channels, which we will discuss in more depth later. These meanders are often self-propagating, and migrate across the floodplain. Often, they have one steep bank and one gentle bank.

9. The fluvial system Braided channels: What do these streams look like?
Braided channels form at deltas but also where streams come out of the mountains and are still carrying high amounts of sediment. They have multiple channels, which are non-vegetated. These multiple channels are confined to an active channel, across which the channels migrate.

10. The fluvial system
Pool-riffle features in meandering or sinuous rivers
Pool: over-deepened channel segment from scour or high discharge events
Riffle: shallow channel segment with rough low-flow water surface
Bar: above flow, locus of sediment deposition during high flows
More specific features: in meandering rivers, a typical morphology will be pool riffle – we’ll probably see some of this.
Thalweg: German for valley. The deepest, and often fastest, part of the channel

11. The fluvial system
Pool-riffle features in meandering or sinuous rivers
An example – unknown location.

12. Meander migration Cut banks erode New sediment deposited on bar
Meander migrates
Planes off a valley
As meander erosion continues, the meander will migrate outwards towards that eroded bank. This carves away the floodplain, as you can see in the diagrams. From meander migration, we get a planed off valley surface that is very important in creating terraces, as we’ll discuss in a few minutes.

13. Incision
A stream’s ability to do geomorphic work is basically dictated by its basal shear stress:
Shear stress = depth * slope * gravity * water density
(Or, if you prefer, Stream power = discharge * slope * gravity * water density)
Shear stress can:
Transport sediment (finer sediment requiring less shear stress to move)
Incise into bedrock (often by abrasion from sediment being transported)
Be dissipated when water interacts with flow obstructions in the channel

14. Incision
Planation forms the valley, but how does a river erode down?
Rivers are at a “graded equilibrium”, where their profiles approximate an inverse log curve
A change to the shape of this curve – i.e. fault uplift – can provoke a reaction – such as incision and knickpoint formation
First though, how does a river erode down – the process we discussed moves the river back and forth, but why might it erode down into its bed?
First, we need to understand the concept of a ‘graded equilibrium’ – this is the profile rivers prefer, due to a balance of gravitational forces and discharge. By profile, we mean the elevation of the channel with downstream distance.
A change or perturbation to this profile puts the river out of whack, and it adjusts itself to regain the graded equilibrium.

15. Incision
Planation forms the valley, but how does a river erode down?
So for example, if we have a fault across the river profile, and it suddenly offsets the river.
Fault

16. Incision
Planation forms the valley, but how does a river erode down?
We get a locally steep point, and the river profile is disturbed.
Fault

17. Incision
Planation forms the valley, but how does a river erode down?
The river upstream of the fault is now going to erode down to return to its previous equilibrium, and there is now a knickpoint (zone of steepened slope)
The locally steepened area is called a knickpoint – which might be called a waterfall, but we use the term knickpoint in fluvial geomorphology. At this point, erosion will be focused, and the river will start to erode here until, propagating the knickpoint upstream until the profile returns to its smooth shape.
Knickpoint
Fault

18. Incision
Planation forms the valley, but how does a river erode down?
The steeper slope at the knickpoint will increase the erosion rate there
Knickpoint will move upstream like a wave
Migration style of knickpoint will depend on bedrock and substrate
As the knickpoint retreats upstream, it can do so in a couple different fashions. The migration style depends on the bedrock type and fracture style, but in all these cases, a pool will form at the base of the knickpoint (just as you’ve observed pools at the base of waterfalls).

19. Knickpoints
There are multiple ways to generate a knickpoint, including:
Differential bedrock strength creating zones of different erosion
Base level drop from sea level changes or rock uplift
Base level drop from faulting across the river
Changes in discharge from stream capture, piracy, or beheading
Anthropogenic influences – redirecting streams, changing surrounding surfaces
Natural or artificial damming
In that example, the knickpoint, which we focus on because it’s the loci for erosion into the riverbed, was formed from tectonic uplift. It can also form though these reasons….
Some of these will propagate upstream, creating a terrace, and some will stay stationary

20. Terraces Alluvium only, bedrock buried Fill terraces
Erosion & planation into bedrock with thin gravel cap
Strath terraces
Incision and planation occur at different times
Paired terraces
One landform we focus on in order to gage the history of the stream valley, are terraces. They come in a variety of shapes and sizes, from fill to strath and paired to unpaired. From a fill terrace, we know the valley must have filled with sediment, then eroded through that sediment. Strath terraces tell a story of erosion only. By interpreting a sequence of fill and strath terraces, we can figure out the valley’s history.
(Do cut and fill history now)
Incision and planation occur together (more common)
Un-paired terraces

21. Landforms
Floodplain: the lowest surface adjacent to the river that is composed of overbank flood deposits overlying laterally accreted alluvium
Point bar: sediment deposited on the inside of meander as meander expands
Cut bank: steep bank on the outside of meander, developed as meander expands
Terrace: abandoned floodplain, product of incision and lateral planation
As knickpoints erode down, and meanders erode laterally, we get a variety of landforms produced. Floodplains form….
Oxbow: abandoned meander bend in the floodplain
Alluvial fan (not shown): conical in shape, loose, coarse sediments from
small channels on steep hillslopes

22. Response timescales
Terraces form due to incision, which we learned has multiple triggers
Thus, a younger terrace might record recent 103 year fault movement, while an older terrace might be due to climate variations on a 104 to 105 timescale
Terrace forming mechanisms occur over different timescales, so we can’t interpret terraces to be formed due to the same process or trigger.

23. The Lane Balance

24. Response Timescales
Terraces aren’t the only features left from the adjustment of rivers to environmental changes

25. Let’s dive into a survey…
Ok, so I think everyone knows how to use a tape – main thing, there’s usually a metric and an English unit side, use the metric side.
Now lets do a survey.
The idea of surveying is to create a flat plane with the autolevel, and measure how far down the topography is from that plane with the autolevel.
So if we are in the middle of a survey, what is everyone doing??
The basic idea: use the autolevel to create a flat plane, and measure how far down from that plane the topography is.

26. Teams of 3: Rod person Level operator Note taker Surveying 101
You will survey in teams of three, with each person having one of the jobs listed above. Rotate jobs so that everybody gets experience all aspects of survying. However, you’ll probably want to keep the same positions throughout the longitudinal profile survey.
Surveying 101

27. Teams of 3: Rod person Tasks: 1. Responsible for the rod
2. Selects suitable measurement location!
3. Waves rod
Ranges ahead for foresights, stationary for backsight
First team member: The rod person, who is in charge of holding the stadia rod. You are in charge of deciding where to make a measurement, so you must be cognizant of any changes to slope or abrupt ground elevation changes.
Surveying 101

28. Teams of 3: Level operator Tasks: 1. Responsible for autolevel
2. Sets up tripod and levels it
3. Sights
Pretty stationary; pivots around rod-person during backsight
The next person, the level operator, sights through the auto-level at the rod person and is responsible for keeping these delicate, pricey instruments safe!
Surveying 101

29. Teams of 3: Note taker Tasks: 1. Takes majority of notes
2. Records all measurements!
3. Plots measurements IN FIELD
Moves between rod-person and level operator
And the notetaker has the busiest job – taking note of the measurements the level operator takes, noting the ground notes the rod person is making, and plotting the measurements. You’ll probably want a calculator as well.
Surveying 101

30. Equipment: The stadia rod
Basically, it’s a very tall metric ruler.
Alternating yellow and white backgrounds indicate meters.
Big numbers give decimeters.
Big filled rectangles are centimeters.
Small filled rectangles are 0.5 centimeters.
Ok, now we can get the equipment out. We’ll go through each piece, except the tape.
First is the stadia rod. Pull it out of its pouch. It’s pretty sturdy. Metric, meters, decimeters, centimeters, half centimeters…
Demonstrate waving the rod. We want it to be upright. It’s easy to see if its leaning side to side, but not front to back, so we wave it. At the lowest elevation, the rod is upright.
Surveying 101

31. Equipment: The tripod
Autolevel base screws into the top of the tripod.
Each leg swings out and its height can be adjusted using the black levers.
Pointed legs secure tripod into ground.
Next, the tripod. Adjustable. Demonstrate how to carry.
Surveying 101

32. Equipment: The autolevel
Knobs adjust focus inside auto-level
Sight in through here
See what is over here
Autolevel rotates on swivel
DELICATE! Carry on your lap during car rides. Demonstrate how to screw into the tripod.
3 toggles fine-tune leveling
Base screws into top of tripod
Surveying 101

33. Let’s dive into a survey…
Ok, so I think everyone knows how to use a tape – main thing, there’s usually a metric and an English unit side, use the metric side.
Now lets do a survey.
The idea of surveying is to create a flat plane with the autolevel, and measure how far down the topography is from that plane with the autolevel.
So if we are in the middle of a survey, what is everyone doing??
The basic idea: use the autolevel to create a flat plane, and measure how far down from that plane the topography is.

34. Weather, objectives, etc. Team names & roles Sketch map
Step 1: General notes
Weather, objectives, etc.
Team names & roles
Sketch map
Well, the note-taker starts out by taking general notes. Where are we? Who are we? Who is doing what? What’s the weather like (yes, this is important, as it determines how well you are doing, as well as stream flow conditions)? A quick sketch of the site, in case you need to return to do the survey again. What direction are you going in? Date?

35. Step 2: Making a measurement
1. “Wave” the rod to get the correct reading:
Now that all the preliminary stuff is done, suppose we are reading now to take a measurement. Here, the rod persons starts out by finding a suitable location. Note that the rod person has put the rod at a change in slope which is a very good place to get a measurement. The rod is waved back and forth to get the vertical reading, which will be the smallest reading.

36. Step 2: Making a measurement
“Wave” the rod to get the correct reading
Optional:
Make 3 readings: upper stadia
horizontal
lower stadia
Distance* = (upper stadia – lower stadia) x 100
Now that the rod is vertical, the level operator needs to take a reading. Looking through the auto-level, there are three lines, and so we will take three readings. The upper and lower lines are used to get distance – the difference (in meters) times 100 is the distance in meters. You can also use a tape. The middle line will have the actual reading used to get elevation.
*Can also use a tape to get distance

37. Step 3: Record measurement
Record the measurements!
Now the note taker needs to record these three readings the level operator is rattling off.
Aside: This is how we set up a notebook. You have a station, backsight, height of instrument, foresight, elevation, distance, and notes column.
In this case, the note person will record the distance as the difference between the lower and upper stadia, and record the height under foresight. They will then be able to calculate the actual elevation (as we’ll see in a minute).

38. Where am I?
Backsighting: measuring to a station of known elevation in order to get your current elevation.
Types of measurements.
There are 2 types of measurements. You always start out with a backsight, which is how you’ll get your actual elevation from a known benchmark. In our case, we will have a benchma.
Station 1
Benchmark
100 meters

39. 1. Record the elevation of the benchmark
100 meters
Station 1
In the notebook, here is how the procedure works. The benchmark elevation is noted. BM
100
Concrete USGS benchmark
1. Record the elevation of the benchmark

40. 2. Record the backsight reading
Benchmark
100 meters
Station 1
2.50
Next, the level operator sites back to the benchmark and the reading (middle stadia hair) is recorded under the backsight column, on the next line down. BM
100
Concrete USGS benchmark
2.50
2. Record the backsight reading

41. 3. Add the backsight to the elevation to get the height of instrument
Benchmark
100 meters
Station 1
2.50
To get the height of instrument, which is the level plane the autolevel creates, we add the backsight to the elevation.
HI = BS + Elev (write on board).
And now you are done with your backsight. The goal of the backsight was to orient where your station is, so the end result is a height of instrument, NOT an elevation. BM
100
Concrete USGS benchmark
2.50
102.5
3. Add the backsight to the elevation to get the height of instrument

42. Where is that?
Foresight: Measuring to an unknown elevation from a known elevation.
Now we know where our station is, we want to start the survey and figure out where something else is. In this case, we know the height of instrument, and need to find the elevation of several points.
Station 1: m

43. 1. Number your location (I prefer station # “.” foresight #)
Again, notebook view. Start by labelling your station. I like to note it by the location – starting with one for the first level location, then a dot, then which fore-sight reading you are on. BM
100
Concrete USGS benchmark
2.50
102.5
1.1
102.5
1. Number your location (I prefer station # “.” foresight #)

44. 2. Record the foresight reading
2.90
Record the reading (middle stadia hair) under fore-sight. BM
100
Concrete USGS benchmark
2.50
102.5
1.1
102.5
2.90
2. Record the foresight reading

45. 3. Subtract the foresight from height of instrument to get elevation
2.90
Now find the elevation.
Elev = HI – FS (write on board). BM
100
Concrete USGS benchmark
2.50
102.5
1.1
102.5
2.90
99.6
3. Subtract the foresight from height of instrument to get elevation

46. 4. Record the distance (tape or stadia distance)
2.90
( )*100
Now we need the distance. You can use a tape, or subtract the top and bottom stadia hairs and multiply by 100 to get the meter distance. BM
100
Concrete USGS benchmark
2.50
102.5
1.1
102.5
2.90
99.6
20.0
4. Record the distance (tape or stadia distance)

47. 5. Don’t forget to make notes about the station (water depth, etc.)
2.90
( )*100
And finally, remember to record where you are! In this case, the rod is on the floodplain, but right at the start of the rise up to the first terrace level (we’ll learn more about these terms on Saturday, and you can read about them some in Harrelson, or on Wikipedia). BM
100
Concrete USGS benchmark
2.50
102.5
1.1
102.5
2.90
99.6
20.0
End of terrace tread, start of floodplain
5. Don’t forget to make notes about the station (water depth, etc.)

48. I can’t see the rod anymore!
Turning point: pivoting your autolevel around a known elevation point to get a better vantage
???
So you keep doing these fore-sights until suddenly, you can’t see the rod – either it gets physically hidden, or its just too far away to read. In this case, you do a turning point – move your instrument by pivoting it around a reading you’ve already taken. You basically make one of your foresights a temporary benchmark.

49. Rod person holds the rod at the last foresight
Level operator moves to a new station
Backsight to the rod to get a new height of instrument
First, you’ve make a foresight to a location. Keep the rod there. Next, using the proper carrying techniques, the level operator moves to a new station with better visibility. Then, since we’ve moved the station, we don’t know the height of instrument and so must do a backsight to the rod location to get a new instrument height.

50. Turning point cont’d. BM 100 2.50 102.5 1.1 102.5 2.90 99.6 20.0 TP
In the notebook, a turning point would look something like this: use TP as the station, backsight reading, new HI, notes, and then the survey can continue. Using my notation, the next point would be 2.1 since we’ve started a new instrument station. BM
100
Concrete USGS benchmark
2.50
102.5
1.1
102.5
2.90
99.6
( )*100
End of terrace tread, start of floodplain
20.0 TP
2.30
20.0
Turning point
101.9
2.1
New station, continuing survey

51. Don’t forget to close the loop!
Why?
Checks for accuracy
Necessary if you’ve done a turning point
After survey is complete, survey back to the original benchmark and compare this measured elevation with the actual elevation.
And before you finish, you’ll need to do one more thing: survey back to the original benchmark. This is necessary if you’ve done a turning point. It checks for accuracy, and gives you error.

52. Note these! Backsight (BS) + Elevation = Height of Instrument (HI)
HI – Foresight (FS) = Elevation
Constantly calculate elevations in the field, and plot your transects in the field to catch any mistakes!

53. Price Creek

54. Price Creek

55. Price Creek

56. Exploring the linkage between subsurface structure, surface faulting,
Tectonic geomorphology and structural evolution of Centennial Valley, MT:
Exploring the linkage between subsurface structure, surface faulting,
and landscape evolution in the wake of Yellowstone.
Claudio Berti, Frank J. Pazzaglia, Pier Paolo Bruno
Istituto Nazionale
di Geofisica e
Vulcanologia
Founded by Lehigh University through the generosity of
Mark and Kristen Koelmel and Chevron Corporation
and University of Utah

57. RED = CF and LRF faults Centennial Valley Lima Reservoir Fault
Centennial Fault
RED = CF and LRF faults

58. Centennial seismic line
Lima Reservoir Fault
Centennial seismic line
Centennial Fault
PC-29.1 well
Earthquake occurrence since Yellow circle 0.3<M<4; Red circle: 4<M<5; (USGS Database)

59. Centennial seismic line
South
North

60. Centennial seismic line
South
North

61. Centennial seismic line
South
North

62. Centennial seismic line
Centennial Fault
Red Rock River
South
North

63. Centennial seismic line
Centennial Fault
Red Rock River
South
North

64. Centennial seismic line
Centennial Fault
Red Rock River
South
North