Watersheds and Rivers

GEOG 205 Fall 2020 – Lab 3: Watersheds and Rivers

Introduction

In Lab 3 you will learn more about watersheds and rivers. Rivers are the most important erosional agent on earth, as they transport the majority of sediment to the oceans and therefore are responsible for impressive amounts of landscape denudation. From concrete urban channels to massive rivers like the Mississippi that drain parts of entire continents, the flow of channelized water is all around us. River processes and landforms are thus both incredibly important and ubiquitous, and Lab 3 will provide you with hands-on understanding of these landforms and how they organize into watersheds (and who knows, maybe you’ll have to get your boots wet too!).

Learning Objectives

• Visit your local river and learn how to put small-scale observations in the context of river processes and patterns observed with larger scale maps and imagery.
  • Interpret and understand how humans modify river systems.
• Use watershed assessment tools to improve understanding of watershed processes and structure, while gaining experience with plotting, visualizing, and interpreting experimental and numerical modeling data.
• Use imagery, existing data, and fundamental published literature to explore river channel patterns.

Instructions and Notes

Make sure to download the file called “g205f20_Lab3Data.kmz” from the week 6 lab content LEARN submodule.

• Lab 3 is worth 18% of your lab grade, and thus 9% of your total course grade.
• Please show your work if applicable.
• Cite all external references used – directly pasting phrases from the internet will result in a grade of 0 for the entire assignment. You should cite these sources in a reference list at the end of the report, but also use in-line citations when appropriate.
• Subsections of labs are listed with numbers, questions that must be answered are listed with letters. So for example, you must answer questions 1.a., 1.b., and so on.
• Submit in either Word or PDF format, and number your responses in the same way they are numbered here. Please put your name and ID number on your assignment. Instructors and TAs don’t like being confused by the submission format!

Lab 3 Questions (44 total marks)

1. (11 marks) Visit your local river – whether it is an urban stream near your house, a wild and beautiful braided river in the Canadian Rockies (yeah, right), or a small meandering creek in a nearby park.
   1. Find a place along the river where it is safe and legal to be, and take a photo or two of the river. Then, find a map of the same location (you can use Google Earth, a GIS, or any other software you are familiar with). Make sure your map is legible and appropriately shows where you took your picture (for some hints on what a good map might include, go here). (1 mark for photo, 3 marks for map).

[insert photo here]

[insert map here]

1. Judging by your photo and map, is your river mostly straight, meandering, braided, or something else? Why do you think that pattern prevails? (2 marks).

6. Browse the Gregory 2006 paper in the Readings subcontent module in Week 6. In particular, see Table 3 to learn about the different between direct and indirect river impacts. In either your map or photo, point out one location of a visible direct modification of river process and/or form. Please circle, draw an arrow to, or otherwise annotate this direct modification and explain what the modification is and what affect it might have on the river (3 marks).

[insert map/photo with annotation here]

1. Explain one indirect modification of river process or form that can be inferred from your image or map. Explain what the modification is and what affect it might have on the river. (2 marks).

2. (19 marks) Access the Ontario Flow Assessment Tool here. Learn a bit about how to use the tool by reading about it under “Steps to run the Create Watershed tool” on the previously linked page. Play around with the tool a little by clicking the “Access the Ontario Flow Assessment Tool”, and get some experience using it before attempting the following questions.

1. Find the town of Conestogo (use the search bar in the upper right hand corner of the tool). Create a watershed just upstream of highway 17 on the Conestogo River (go to OFAT à Create watershed…). Name it Conestogo. If it does not work, try a few times (you might have to refresh the page). You should get a watershed that looks like this:. Under watershed characterization, calculate the drainage area and report it here. (1 mark).

1. Now that you know how to create watersheds and characterize them, we can use these data to analyze this and other watersheds. In your Conestogo River watershed, extract land cover (land cover tab). What are the top 3 land covers in the watershed, by percent? Include the percent. (1 mark).

3. Run the Mean Annual Flow (MNR 2003) hydrology model on the Conestogo River watershed. Report the mean annual discharge (in m³/s) and the total volume of discharge per year in km³. (2 marks).

1. Run the Flood Flow: Index Flood Method with EPA hydrology tool and view the results. Plot the data in Excel or another plotting program – go here or find your own guide on how to plot in Excel or your chosen program if you are unfamiliar. It is up to you how to structure the plot, but you should find a relationship between recurrence interval and discharge (in other words, you will plot year vs discharge). Attach the plot you created below, and in a few sentences explain what the relationship means (in particular, mention if your relationship is linear, exponential, power, or something else – if you don’t know how to do this, look it up before asking!). (3 marks).

[insert plot here]

2. Using the relationship from question 2.d, what is your estimation for the flood discharge with a recurrence interval of 75 years? (1 mark).

2. Using the relationship from question 2.d, what is your estimated recurrence interval of a flood with a discharge of 450 m³/s? (1 mark).

1. If the 10% of the swamp land cover in the Conestogo River watershed is transformed into infrastructure land cover, would the mean annual discharge and flood discharge change and in what way? If so, why or why not? (2 marks).

1. A “scaling relationship” that compares drainage area and discharge is often used in studies of rivers and watersheds because it is significantly easier to measure drainage area than it is to measure discharge. Why do you think that is? (1 mark).

1. If you can measure both drainage area and discharge in a number of watersheds, you can use the relationship to estimate discharge in other watersheds by simply calculating drainage area. Using the same process you used for the Conestogo River watershed, find the watershed area and mean annual discharge for the following rivers (hint, use “Create from Coordinate” instead of “Create from Map Point”): (3 marks).

42. Grand River at Maitland: 42.864981 N, 79.575459 W
43. Whiteman’s Creek near Paris: 43.153338 N, 80.352763 W

• Canagagigue Creek near Elmira: 43.573474 N, 80.490907 W

43. Cox Creek near Elmira: 43.582111 N, 80.446814 W

2. Using the values from 2.h and drainage area and discharge values for the Conestogo River watershed, produce a plot that relates drainage area to mean annual discharge. Include a line of best fit, with its equation. (2 marks).

[insert plot here]

2. The Thames River watershed in Ontario is 5,825 km². Using your answer to 2.i, find the mean annual discharge of the Thames River. Then, find a source for the measured mean annual discharge. Cite the source and the value.(2 marks).

3. (14 marks) A foundational study (Leopold and Wolman, 1957) on river patterns found that in general rivers that are steeper and have higher discharge are more likely to be braided:

The line (which the authors drew on their own, based on judgement) discriminates between meandering and braiding – points that plot above the line are likely to be braided and points that plot below the line are likely to be meandering. Keeping this plot in mind, answer the following questions.

3. Open the “g205_lab3.kmz” file in Google Earth and go to the “Root River Braided/Meandering Transition” point. Upstream of the point, the average slope of the river is about 0.001. According to the plot above, about what is the minimum discharge required for the river to be braided? (1 mark).

1. What do you think occurs at the transition point to change the channel pattern to meandering? Explain and provide support for your claim – support with imagery or calculations is stronger than qualitative support. (3 marks).

1. Leopold and Wolman’s plot suggests that straight channels can occur in high or low slope environments but that they must have low discharges. Find two locations on Google Earth where you can see straight river sections – one with high energy (slope) and one with low energy. Paste screenshots and explain where these are located. Cite any outside information used. (3 marks).

[screenshots here]

1. Where else might you expect straight channels? (hint: consider human impacts to rivers) Explain why this other kind of straight channel exists and attach a screenshot of where on Google Earth you found this type of straight channel (2 marks).

[screenshot here]

1. Go here to look at a river in Borneo in Google Earth Timelapse. Look around at the river, other rivers, and the landscape. Describe what you think is happening to the river, and why. Specifically mention how the river pattern might appear to be changing. (2 marks)

3. Considering Leopold and Wolman’s 1957 plot above, what do you think is more likely to be changing in question 3.e – slope or discharge, and why? (1 mark)

3. Considering what you see in question 3.e, name and explain at least 1 variable you think is missing from Leopold and Wolman’s 1957 plot. (2 marks)

References

Leopold, L. B., & Wolman, M. G. (1957). River channel patterns: braided, meandering, and straight. US Government Printing Office.