How I taught Streamflow Generation online in Spring 2020

This post is part of a series in which I provide the details of each unit I taught post-transitioning to online in Spring 2020 in the Watershed Hydrology class at Kent State University. For more context about the course and my perspective on it, please read the introductory post. [I’ve added some bracketed notes about things I’d change up for a future online offering.]

Overview of Streamflow Generation Unit

We’ve talked about how water goes down (precipitation), up (evapotranspiration), and down (infiltration).  Streamflow is the last major term in the water budget – but before we can talk about streamflow we’ve actually got to get the water into the stream (or wetland or lake or …). That’s what we’re going to study now. 

I made a video to introduce you to this topic and define a few key terms. Watch this first and then proceed to work your way down this page watching videos and reading content as you go. 

The slides that accompany this video can be found here.

Learning Objectives

1. Distinguish between baseflow and stormflow (also called quickflow) and explain when each occurs
2. Describe the conditions that generate infiltration-excess overland flow and where it is likely to occur
3. Describe how saturated overland flow works and explain how it is different than infiltration excess overland flow
4. Explain the requirements for subsurface stormflow and discuss the sequence of events that occurs for it to be produced
5. Discuss how the variable source area concept is related to subsurface stormflow and saturation overland flow
6. Illustrate the different connections that can occur between groundwater and streams and lakes
7. Explain how groundwater pumping can affect streams
8. Analyze how streamflow generation mechanisms affect stream peak flows and lag times
9. Define velocity and celerity in the context of hydrology
10. Discuss how climate, topography, soils, and geology influence the streamflow generation mechanisms that operate in a watershed
11. Examine how human actions can influence streamflow generation mechanisms and associated hydrograph characteristics

What is streamflow generation?

Terminology note: In the video above and in other resources listed below, you may see the phrase “runoff generation” used. I prefer the term “streamflow generation” because I’m interested in all of the ways that water gets to streams (or other water bodies), not just ways that involve surface runoff or overland flow. I also use the term streamflow generation to talk about how we get baseflow (i.e., water in the stream between storms), which is not runoff. 

Required Reading

The Runoff Processes website (from the COMET international edition) has short pages of text accompanied by good animations of the processes being discussed. You should work your way through:

• Overview of Runoff
• Paths to Runoff
• Basin Properties
• Soil Properties (this should be a review from our infiltration section)
• Modeling Concepts (recommended, but not required)
• Summary

Take the practice multiple choice quizzes at the end of each section to check your comprehension.

You should also read Chapter 5 pages 125-138 in your Brooks et al. textbook, if you haven’t already done so.

Details of the Streamflow Generation Mechanisms

I created video lectures discussing infiltration-excess (Hortonian) overland flow (HOF), saturation overland flow (SOF) and the variable source area concept, and subsurface stormflow (SSF). I’ve already posted those videos in a separate blog post, with some wrap-around text. You can read the blog post here.

If you or your students just want the slides I used, you can get the HOF ones here, SOF ones here, and SSF ones here. If you use them, please credit me and Cornell University’s Dr. Todd Walter for the animated sequences. Dr. Walter also has an excellent page with more details of infiltration-excess overland flow and one on saturation overland flow.

More about Groundwater and How it Interacts with Streams

Every year, some students in my class have had a full hydrogeology course, while others know nothing about groundwater. I have struggled to find the right approach to teaching groundwater basics within the confines of a broader watershed hydrology class, while not boring/overwhelming my students depending on their background. I’ve decided that focusing on groundwater-surface water interactions is the way to go. The video below by Ken Bradbury provides an excellent introduction to the topic and I think hits the mark better and more concisely than I have ever done in person.

The video was produced by the American Geosciences Institute (AGI) and is actually part of one of three that together make a nice hour-long seminar on Water as One Resource, with multiple presenters. You can access all three parts, the associated slides, and even quizzes through the AGI Geoscience Online Learning Initiative website. Ideally, I’d love to have students complete the whole sequence, which I think would be appropriate for both those with and without a hydrogeology course under their belt. But in the interest of simplifying log-ins and content during this highly unusual semester, I opted for just the video shown above.

How flow generation controls stream hydrographs

I’ve written this as a blog post to help you make the connection between what’s happening on/in the hillslopes to what happens in the stream. The different flow generation mechanisms affect the way a stream responds to rainfall. How quickly does the water start to rise? And how high do the peak flows get? (Estimated reading time: 10-15 minutes)

Zooming Out: How climate and landscapes control flow generation

This is another blog post I wrote, in which I try to put the flow generation mechanisms in context of watershed characteristics. We’ve been talking about watershed characteristics all semester long, and here is yet another way that they are important for understanding (or even predicting) what happens in the streams. (Estimated reading time: 7-10 minutes)

Masterclass on Streamflow Generation

This is totally optional and not in any way required for anyone, but if you think that streamflow generation mechanisms are just about the coolest thing that you’ve ever heard of, then you can learn so much more about them from one of the world’s leading experts on hillslope hydrology: Jeff McDonnell in this 3 hour short course (requires flash).

When I was a graduate student I got to take a 10 week hillslope hydrology class with Dr. McDonnell and it changed the way I think about the world beneath my feet. Listening to 3 hr recorded presentation isn’t nearly as good, but you could still learn a lot if you want to do a deep dive.

Assessment

• A 10 question multiple choice quiz, drawn from a bank of more than 10 questions, which students had the opportunity to take twice.
• Questions on the final exam.
• I don’t have a problem set that accompanies this unit, but I’d love to hear how others treat this topic quantitatively or in terms of data interpretation in a similar course.

Please respect my work

This work (my videos and blog posts) are licensed under an Attribution-NonCommercial-NoDerivs 3.0 Unported (CC BY-NC-ND 3.0). That means that you need to give appropriate credit if you use or modify anything I’ve posted here. It also means that you can’t use the material for commercial purposes. If you want to use other resources I’ve listed above, please respect the rights of the originators. If you want to use my sequencing of topics and resources in your class, by all means, go ahead.