Lesson 10: Water in California
This week's lesson is the first of several we'll have that explore a specific topic rather than a geomorphic province, and its focus on water could not be more timely. Currently, mountain snowpacks are at or above normal levels for this date and it looks like the state is on track to have a good water year. If the spring storms do not arrive or we have an exceptionally hot summer, however, competition among agricultural uses, environmental needs, and the state's growing population could still spell trouble. In addition, with climate change and particulate pollution predicted to reduce mountain snowpacks by as much as 20% in coming years water shortages in California are only likely to be more severe. That's why it's important for every Californian to understand where and when precipitation falls across the state and how that water moves through surface streams and underground aquifers.
In chapter 10 Harden briefly describes the distribution and timing of precipitation across California and the overland flow of water in streams (like Roaring River in Kings Canyon National Park, right) that erode, transport, and deposit of sediment as part of "dynamically balanced" river systems. She also describes the movement of groundwater through aquifers and highlights the problems we're seeing in California as overdraft and contamination of groundwater damage this critical resource. Finally, this week's exercise introduces you to the techniques geologists use to measure the amount of water moving through a stream channel at a given time.
As you read about California's surface and groundwater resources be sure to take careful notes on the topics covered by the learning objectives below, but don't worry about trying to remember the details of the specific case histories the author sites as examples. As usual, writing out key facts in your own words or making neatly labeled drawings will help you better understand the significance of what you've read and spot any gaps in your knowledge. Having good notes will also make it easier for you to review for this week's quiz and and access what you've learned when you want to refer back to it for future assignments. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page.
Weekly Learning Objectives
Upon successful completion of this week's lesson, a student is expected to be able to:
- Describe how the location and seasonal timing of precipitation vary across California, and how this distribution does or does not meet the state's needs based on its agricultural usage, environmental commitments, and population.
- Outline how streamflow and groundwater recharge depend on the amounts of precipitation that are partitioned into evaporation, infiltration, runoff, and transpiration.
- Calculate the discharge of a stream given data on its cross-sectional area and average velocity, and describe how hydrologists calculate the discharges of streams with irregular channel cross-sections (Exercise 10).
- Describe the three types of load that streams carry, and explain how the amount of sediment a stream moves is likely to change as the water slows down upon entering a lake or spills out across a floodplain. (Note that two of the three types of load we're considering here are lumped together as "mechanical load" by Harden.)
- Explain how the water table is defined within an aquifer, and how the flow of wells differs depending on whether they tap a confined- or unconfined-aquifer.
- Describe the difference between the porosity and permeability of rock units, and indicate which property is more important in order for a given unit to serve as an aquifer.
- Cite the two major problems—in addition to simply depression of the water table—that result from groundwater overdraft, and indicate one area of California that has either suffered from or is vulnerable to each.
- Outline the common sources of groundwater contamination that occur in California, and briefly describe how hydrologists assess where and how severe contamination is.
Reading and Browsing Assignment
- Read Chapter 10, being sure to focus on the topics outlined in the learning objectives above.
- Browse through the discussion of streams and how they work in the stream hydrology section of the Water Encyclopedia. This discussion covers some topics in a little more depth than our text, and can serve as a supplement or "second opinion" if something you read in the text is a bit unclear.
- Browse through the brief introduction to ground water hydrology given by the Ground Water Advocates Coalition, a citizen's group concerned with ground water issues near Issaquah, Washington. This is a very "user friendly" webpage, and like the stream hydrology site above is intended to supplement the introduction to ground water in our text.
- Finally, there is a tremendous amount of data about California's streams on the Web at the California Data Exchange Center. This portal will take you to real-time or near real-time data on river discharges, snowpack amounts, statewide water conditions, and more. For example, to find out the current discharge of the Shasta River near Yreka, click on "River Conditions " in the menu near the top of the page; next, click on "Klamath River and its tributaries"; and finally scroll down to the graph for discharge of the Shasta River. When I checked this morning the river's discharge was about 250 cfs (cubic feet per second), but it has been up as high as 350 cfs due to storms during the past few weeks. (If you click on the text below the graph you can request a custom display of discharge over any time period you wish, and you can follow the river's recent behavior.)
Exercise 10: River Discharge (Due by 9:00 AM on 21-Mar-2011)
Part of this week's lesson looks at rivers and river systems in California and so, to learn more about how geologists measure stream discharges, please point your browser to the Virtual River website. This is the gateway to the two different exercises: River Discharge and River Flooding. Click on River Discharge and work through the exercise to learn how geologists actually measure how much water is moving through a river's channel at a given time. Like Rb/Sr isochron exercise we worked on a few weeks ago, River Discharge uses Java applets—so be patient while they load. Feel free to contact me if you have any problems, but if you do please makde sure to note of the page and question you had trouble with. (Also, unfortunately, if you exit the exercise before you finish you will have to start over again.) When you have completed the exercise fill in your name and school, view the certificate of completion, right-click on the blue part and select "Save image as...", and save the image of the certificate. (You may want to open the file to make sure you got the certificate before you dismiss the webpage.) Then go to Exercise 10 in the Etudes "Assignments, Tasks, and Surveys" tool send your certificate image to me as an attachment.
If you would like, after you're done with River Discharge you can return to the Virtual River page, click on River Flooding, and try that exercise as well. River Discharge is a fairly short assignment (about 1 hour) but River Flooding is longer and more challenging. I am not making it a class assignment because there is not much discussion of flooding and how flood recurrence intervals are determined in our text.
Quiz 10: Water in California (Due by 9:00 AM on 21-Mar-2011.)
After you feel you have met the learning outcomes outlined above (including those covered in Exercise 10) please complete Quiz 10 in the Etudes "Assignments, Tests, and Surveys" tool. There are ten questions about surface and ground water in California and each is worth one point. If you can answer all of them correctly it means that you know your way around the geology of water pretty well and are ready to start learning about California's Great Valley next week. Like all of our weekly quizzes, this one is timed (you'll have 30 minutes) and must be completed in one "sitting". (That is, you will only be granted access once.) So, be sure you're ready to complete your quiz when you start it—and be sure you're using Firefox. Good luck.
