Lab 19: Fluvial Geomorphology and Landforms

Katie Burles and Crystal Huscroft

Water in streams is one of the most widespread and important agents of erosion and deposition on Earth. Flowing water has the ability to free rock material, set it in motion, and then transport materials downstream to depositional environments. These stream-related geomorphic processes produce predictable fluvial landforms. While predictable, these landforms are dynamic and routinely shift over time.

This lab activity will provide students with satellite views of fluvial landforms around the world using Google Earth. Students will demonstrate their understanding of fluvial geomorphology processes and associated landforms by creating an annotated virtual guided fluvial landform tour.

Learning Objectives

After completion of this lab, you will be able to:

  • Identify, interpret and sketch fluvial processes and their characteristic landforms using Google Earth imagery.
  • Differentiate braided and meandering channel patterns and provide evidence for why they formed.
  • Identify locations of erosion and deposition in streams.
  • Locate and describe common landforms of meandering streams and floodplains.
  • Demonstrate understanding of local base level in streams.
  • Calculate stream gradient for different channel patterns.

Pre-Readings

Introduction to Fluvial Geomorphology and Landforms

Understanding of the following key terms is required for this lab. If you are unfamiliar with any of these terms, look them up before continuing.

Abrasion Depositional environments Meanders
Aggradation Flooding Oxbow lake
Base level Floodplain Point bar
Braided stream Fluvial erosion Stream discharge
Cut bank Fluvial fan Stream sorting
Cutoff Meander necks Stream velocity
Delta Meander scar Thalweg

Instructional Tour in Google Earth (Web)

Before proceeding, download and go through the KML file Instructional Tour: Fluvial Geomorphology Lab on your computer or Google Drive. Open Google Earth (Web) (NOT Google Earth Pro). Select NEW PROJECT and IMPORT KML FILE FROM COMPUTER OR GOOGLE DRIVE. Select PRESENT.

Take your time to zoom in and out at each location to view the specific examples. Please note there is no audio for this tour. Alternatively, click here to view a PDF document with screen captures of the instructional tour. Complete the instructional tour provided to learn more about how to find and draw the fluvial features included in the virtual guided tour.

Calculating Gradient

Water flows from higher elevation to lower elevation on the Earth’s surface. The gradient (slope) of a stream influences not only the channel pattern (braided or meandering) but also its discharge, velocity, depth, width and ability to transport sediment. In order to get a sense of the processes operating on a segment of a stream, and in preparation for fieldwork, stream hydrologists will regularly determine stream gradients.

The gradient or slope of a stream is calculated by the difference in elevation between 2 points on a stream divided by the distance between the 2 points following the channel where water actually flows. When using paper maps, the elevation change of the stream is estimated by determining the elevation of the start and end point of the reach using contour lines and the distance of the stream is measured by measuring the distance travelled with a ruler. For this lab, measurements will be collected in Google Earth (Web). When measuring the distance of the stream we must follow the path of the stream and not just a straight line distance (unless the reach of the stream is straight).

After obtaining the elevation change and the distance between two points, gradient can be calculated and expressed in 1 of 3 ways:

  1. In elevation fall per channel reach distance (m/km): = elevation (m) (rise) / distance (km) (run)
  2. As a percent (%):
  3. As an angle (degrees) (Figure 1):
Figure 19.1. Slope Calculation. Source: Crystal Huscroft, CC BY-NC-SA.

Example: If a stream drops 100 m over a 1km distance, its gradient is 100 m/km, 10%, or 5.7 degrees.

Low-gradient streams are almost flat and have very little slope, whereas high gradient streams indicate a steep slope.

Gradient is a key control of stream velocity, which in turn controls sediment erosion and deposition in a stream. Water in high-gradient streams can move more rapidly (i.e., have a higher velocity), and therefore can be capable of carrying coarser sediment. In contrast, low-gradient streams with slower velocities will only be able to carry finer sediments.

Attribution Guidelines for using Google Earth Content

All uses of Google Maps and Google Earth content must follow specific attribution guidelines. Students submitting screen captures of all stops on the virtual tour created in Exercise 1 must therefore follow attribution guidelines for using Google Earth content.

Screen captures must include the Google logo and third-party data providers in the imagery (Figure 19.2). This attribution information is shown on the bottom of the screen. The size of the attribution text must be readable for the screen capture.

Figure 19.2. Google Earth screen capture, including Google logo and third-party data providers. Used in accordance with Google Earth terms and conditions.

Lab Exercises

This lab includes two exercises:

Exercise 1. Create a virtual guided tour of fluvial landforms using Google Earth (Web).

A list of features is provided in the lab exercise, and each feature will be a stop on your tour. For each stop you will provide a detailed description of how the feature formed, including clear evidence and observations. Consider any human interference or land use near the features.

This exercise will take around 1.5-2 hours to complete. The length of time allocated to this exercise will depend on your familiarity with Google Earth (Web) and how well you understanding fluvial features.

Exercise 2. Calculate the stream gradient for two different streams included in Exercise 1.

Both gradient calculations will be included as stops on the tour. For each calculation, you will draw an accurate line following the thalweg of the main channel of the stream reach, and provide a detailed list of measurements and calculations.

This exercise will take around 0.5 hours to complete. Similar to Exercise 1, the length of time allocated to this exercise will depend on familiarity using Google Earth (Web) and gradient calculations.

EX1: Create a Guided Fluvial Landform Tour

Open Google Earth (Web), NOT Google Earth Pro. From the PROJECTS menu on the left of the screen, select New Project. In the drop-down options, select Create KML file. Edit the title to include your last name, then first name, student number, and lab number <Doe John c0453993 L19>).

The PROJECT will be the basis of the Guided Fluvial Landform Tour. Some background research may be required to find good locations for the various fluvial features. Alternatively, the lab instructor will provide specific regions to focus the tour.

In the SEARCH menu on the left of the screen type in the name or coordinates (LAT/LONG) of the starting location.  Your starting location should be a delta feature (see Table 19.1).

To navigate Google Earth (Web), become familiar with the tools available on the bottom right of the screen.

  • Zoom in and out using the – and +
  • Options to view imagery in 2D or 3D
  • Compass arrow allows the user to change the cardinal direction of their view

To create the PROJECT become familiar with the tool available for creating NEW FEATURES. There is a tutorial available on Google Earth (Web) that demonstrates this. There are lots of icons available to customize placemarks, lines, or shapes. Name your project Lastname,_Firstname, Fluvial Geomorphology (eg. Doe, John, Fluvial Geomorphology).

  • Add Placemarks to add a point in the tour.
  • Draw a line or shape to clearly identify the features.

Select the first feature, then click on NEW FEATURE.

  1. In the name box, type in the name of the feature and your last name (ex. Meander scar, Doe).
  2. EDIT the feature. In the info box, type a description of the feature, including evidence and an explanation of how this specific feature was formed. Be as specific as possible. It may be interesting to note any evidence of human interference with the feature that may have influenced its development.
  3. If possible, add an image to further enhance the tour. If using images from the web, proper image attribution must be included.

For the PROJECT find examples of each of the fluvial features listed in Table 19.1. Add them to your tour in the same order as they are listed in Table 19.1 (i.e., the first feature on your tour will be a delta). Use the middle column to help you identify and describe the landforms. Add any details or annotations listed in the right-hand column of the table.

When finished, try watching the presentation of the tour. Each feature above MUST be in the order described in Table 19.1.

 
TABLE 19.1 Description of Features and What to Look for in Google Earth (Web)
Feature
What to Look For (This information is included in the Instructional Tour) Details to Add
 

 
1. Delta

A stream delta is an accumulation of sediment that forms where a stream reaches base level (i.e. lake or ocean).

  1. Locations where streams enter a standing body of water such as ocean or lake
  2. Distinct pattern of drainage often similar to branching of tributaries.
  3. Deltas are often triangular in shape (resembles the Greek letter delta (Δ)), but not all deltas take this shape.
  4. The shape may depend on the stream’s sediment load, influence of water currents in the other body of water, and whether or not surrounding land prevents the spreading of the delta sediment.
Outline the location of the delta, if possible.
 

 

2. Fluvial Fan

A fluvial (alluvial) fan is a gently sloping, broad cone shaped accumulation of water-transported sediment deposited where a stream exits stepper topography and flows onto gentler ground at the base of a mountain range.  

  1. Often cone-shaped.
  2. The apex (higher elevation) is the narrowest part of the fan and the apron (lower elevation) is the widest part.
  3. Can range in size from the very small to the truly massive (the largest are often seen best from space).
  4. Evidence of multiple stream channels on the fan surface. (When water flows through channels on the alluvial fan it only occupies a small portion of the fan at any one time. Over many centuries or longer, the streams will migrate from one side of the fan to the other, building it up.)
Outline the location of the fan, if possible.

3. Braided Stream

A stream that forms from multiple intertwining channels around sediments in the streambed.

  1. Multiple channels.
  2. No or little (young) vegetation on islands commonly shaped like rounded diamonds of gravel or sand between channels.
  3. High sediment load.
  4. Most originate from glaciated areas, but they can form in other settings downstream from large quantities of sediment such as volcanoes.
  5. Often found downstream of terrain that experiences significant erosion, including mountain ranges.
  6. Can occur in low-gradient areas with abundant fine sediments like deserts.
  7. Common pattern on alluvial fans.

4. Meandering Stream

A meandering stream has a single channel with a snake-like (sinuous) pattern.

  1. Streams channel resembles snake-like (sinuous) pattern with a series of broad loops.
  2. Mid-channel bars (islands) will be uncommon and have established vegetation.
  3. Streams migrate laterally by sediment erosion on the outside bend of the meander and deposition on the inside of the bend.
  4. Numerous oxbow lake (filled with water) and abandoned channels may be located in the flood plain surrounding the stream.
For the meandering stream above (Feature 4), include each of the features listed below (Features 5-13)

5. Point Bar

An accumulation of sediment that forms along the inside edge of a stream meander. This is a depositional feature.

 

  1. Located inside of the meander.
  2. Point bars will gently slope towards the water edge.
  3. Obvious sediment accumulation when stream level is low, has little to no vegetation, and appears light-coloured.
Outline the location of the point bar.

6. Cut Bank

Cut banks form on the outside edge of a meander where steam flow is highest. This is an erosional feature.

 

  1. Located at outside edge of the meander.
  2. No deposited sediment.
  3. Often a steep slope between the steam edge and surrounding vegetation on the flood plain.
  4. Narrow band or no light-coloured sediment exposed.
Trace the cut bank.
7. Stream Meander

A meander is a looping bend in a steam channel.

Meander will be one of a series of sinuous curves in the steam. Trace the stream meander.
8. Neck

Meander necks form as meanders converge due to erosion along two cutbanks. Once the neck shortens, the two meanders join. The main flow of water (the thalweg) will abandon the meander and flow across the neck. The existing meander will eventually form an oxbow lake.

Locations where two cuts banks on meanders are narrowing the distance between two meanders. Draw a line between the two meanders to distinguish the neck.
9. Cutoff

When the meander neck closes, a cutoff forms where the two meanders join.

  1. Straight new stream channel section adjacent to a newly formed oxbow lake.
  2. In some locations the edge of the new stream channel will have natural levees separating the new channel and the oxbow lake.
Outline a location where a meander has been cut off from the stream.
10. Oxbow Lake

An oxbow lake forms when a meander is cut off from the channel.

 

  1. Meander full of water separated from the main channel
  2. Adjacent to a suspected oxbow lake will be a cutoff in the main channel
  3. Artificial leeves may separate the oxbow lake and the main channel.
Outline the oxbow lake.
11. Meander Scar

Meander scars are oxbow lakes that are now filled with sediment and vegetation.

 

  1. Evidence of past oxbow lake adjacent to stream cutoff.
  2. Often filled with young vegetation and can be important wetland areas.
Outline the meander scar.
12. Future Oxbow Lake

An oxbow lake forms when a meander is cut off from the channel. You will notice a cutoff starting.

 

Evidence of a cut off that could form an oxbow lake in the future. Draw in where a future oxbow lake could occur in the meandering stream.
13. Local Base Level

Streams stop flowing when they reach base level. Local base level can form when the stream is dammed naturally (such as beaver dams or landslides) or artificially by people (such as an artificial lake called a reservoir).

 

  1. Follow the stream channel until it reaches a local base level or ultimate base level (ie. sea level).
  2. Look for delta features.

NOTE: Depending on the stream this could be sea level, a lake, or a larger stream.

Placemark a local base level.

EX2: Calculate Steam Gradient

Using Google Earth (Web), calculate the approximate stream gradient (of the slope of the stream slope) for both the braided and channelized stream selected in the first set of Exercises.

Find 20 m of elevation loss in the main channel of each stream by hoovering the pointer (mouse) over the channel and reading the elevation from the bottom right corner of screen.

ADD a NEW FEATURE and DRAW a line between the upstream (higher) elevation and downstream (lower) elevation of the stream reach that represents 20 m of elevation loss. Remember to follow the path of the channel and not just the straight distance. Note the general direction of flow of this stream. These lines will be features #14 (braided) and #15 (meandering).

MEASURE the channel length distance using the MEASUREMENT tool located on the MENU on the left side of the screen. Collect the measurement following the feature line following the path of the channel.

EDIT the FEATURE Description and add the following information about the gradient calculation:

a. Upstream Elevation = ___ m

b. Downstream Elevation = ___ m

c. Difference (rise) = __ m

d.Channel Length Distance (run)  = ___ km

e. Gradient = ___ m/km

f. Gradient = ___ %

g. Gradient = ___ degrees

Reflection Questions

Please take 15 minutes to answer the following questions.

  1. Reflecting on the imagery in Google Earth respond to the following questions:

a.  Is the imagery in real-time? Why or why not?

b.  Are the braided and meandering streams observed at high or low stream discharge? Support this answer with evidence from the exercises.

  1. Compare and contrast the gradients calculated in Exercise 2 for the two streams included in Exercise 1. Does the calculated gradient tell you whether the stream will erode, transport, or deposit sediment?  What other information would you need to learn in order to make a more informed answer to this question? Explain your answer.
  2. What are the limitations of measuring gradient using Google Earth?

Worksheets

Lab 19 Instructional Tour PDF file

Media Attributions