Calculation of Stream Discharge Required to Move Bed Material
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Students will measure stream velocity, depth, and grain sizes across two channel transects. After constructing both a longitudinal profile and two cross sections, students will calculate the discharge required to move the bed load.
This activity is used in the Sedimentology course, a 300-level geology course.
Skills and concepts that students must have mastered
Students need to be able to construct cross sections, measure flow velocities, and estimate grain sizes.
How the activity is situated in the course
The activity is a stand-alone exercise, but its strength is the field application (i.e., collecting, analyzing, and interpreting data) of previously covered information to answer a practical geologic problem.
Content/concepts goals for this activity
The goal is to show the students how geomorphic features relate to physical processes and how these processes can be examined quantitatively.
Higher order thinking skills goals for this activity
The thinking skills involve setting up the field work so the necessary data can be collected. Students will need to quantitatively analyze the data to relate theoretical relationships to geomorphic processes and features.
Other skills goals for this activity
Other skills involve using an auto level and a digital current meter.
Description of the activity/assignment
Students will map two sections of a stream and calculate the depth, velocity, and discharge of flows required to move the stream bedload. Students will produce two cross-sectional profiles of the stream, one through a pool and one through a riffle section, and one longitudinal profile. Measurements of sediment size, depth, and velocity, will be determined at meter intervals across each cross transect. Students will also calculate the approximate cross-sectional areas across the pool and riffle sections and associated discharges. Students will also determine the stream gradient along the longitudinal profile. From these data, students will employ hydrodynamic equations to calculate the critical shear stress, and mean flow velocity required to move the bedload. Students can then calculate what the discharge and stream width would be at the time of sediment movement, and compare these data with those calculated for "normal-flow" periods.
Determining whether students have met the goals
I grade the maps and profiles the students produce, their quantitative results, and their conceptual answers to associated questions.More information about assessment tools and techniques.
Teaching materials and tips
- Activity Description/Assignment (Acrobat (PDF) 316kB Dec10 07)
- Jeff Clark, Lawrence University, Quantitative field activity: Discharge and Sediment Transport in the Field (http://serc.carleton.edu/quantskills/workshop05activities/clark.html)
- Grant A. Meyer, Univ. of New Mexico, Field Lab for Hydrologic and Sedimentologic Controls on Stream Channels (http://epswww.unm.edu/faculty-and-staff/meyer/)
- John Pitlick, Univ. of Colorado, Fluvial geomorphology lab exercise: movement of bed material (http://www.colorado.edu/geography/john-pitlick-0)