Digitization and Volumetric Analysis of Sediment Transport in a Simplistic Flume
C. Robin Mattheus, Hamilton College
SummaryThe activity is designed to help students conceptualize the spatiotemporal relationships between erosion and deposition across a convex topography, which serves as a proxy for understanding rill and gully formation, knickpoint migration, valley excavation, and the interplay between sediment supply and accommodation across distributary features. The exercise utilizes simplistic flume observations and measurements to generate digital terrain models (DTMs) of generated topographies; by changing individual flume parameters between experimental runs (such as discharge, slope, and sediment type and moisture content), students are able to determine controls on sediment dispersion.
Type and level of course
This exercise was designed to actively involve students throughout the course of a semester in the various aspects of sandbox construction, experimental design and execution, data analysis (observatory and GIS-based), and presentation. The amount of time invested in this project is dependent on the scope of the experimental design and student involvement (with sandbox construction, setup, and data entry); this experimental blueprint calls for at least 5 hours of lab time, which may be spread out over several lab periods to accommodate for relevant homework assignments and student input on experimental setup and design.
Geoscience background assumed in this assignment
A geoscience background that includes physical geology and/or sedimentology is preferred, but not essential; useful background information before lab should include a discussion on surface hydrology as well as erosional and depositional processes along hillslopes.
GIS/remote sensing skills/background assumed in this assignment
It is assumed that students possess basic GIS-skills (i.e. an understanding of coordinate systems, data types, data import and display, outputs and layouts, etc.).
Software required for this assignment/activity:
ArcMap 9.2 with Spatial Analyst extension (ESRI)
ArcScene with 3D Analyst extension (ESRI)
Surfer 9 (optional gridding software)
Time required for students to complete the assignment:
Dependant on student involvement in flume construction and scope of assignment
GIS/remote sensing techniques students learn in this assignment
In this activity, students will learn how to format and import point-data they generate themselves from elevation measurements taken in the flume box into ArcMap. Point-data are interpolated to generate raster surfaces. Students are asked to generate a timeseries of these surfaces, representing topographies at specific instances in time during the evolution of the flume landscape. Using simple calculator functions in ArcGIS, students can generate net-change maps that document the spatial and temporal distribution of erosion and deposition and allows sediment volumes to be calculated.
Other content/concepts goals for this activity
This exercise should help students conceptualize geomorphic processes such as incision, knickpoint migration, and alluvial-fan development and contribute to their understanding of how changes in gradient, discharge, and sediment characteristics effect rates of erosion and channel-profile equilibration. Ultimately, students should be able to relate model observations to naturally-occurring analogues (i.e. rill, gully, and incised-valley formation and evolution) and identify the spatial and temporal scaling issues presented by the use of a simplistic, down-scaled models to explain 'real-world' processes.
Higher order thinking skills goals for this activity
- Experimental design to test formulated hypotheses
- Data analysis and critical evaluation of generated models
Description of the activity/assignmentThis exercise requires construction of a watertight box to serve as a flume, approximately 5 lbs of fine-grained sand, two buckets, tubing, clamps, a stop watch, digital camera, nails, and thread. Sample instructions on flume construction and setup are provided under supporting materials. It takes several hours to put this particular flume together, provided necessary materials and tools are available. Background materials are useful in preparing the students to formulate hypotheses and develop an appropriate experimental design to put them to the test. Charlton (2008) provides a good overview of water erosion on hillslopes in the 'Sediment Sources' chapter. Ethridge et al. (2005) give a thorough overview of the evolution of flume studies; the experiments designed to investigate the role of coastal-plain convexity on incision are particularly applicable to this exercise. Using this simplistic flume design, students will have an opportunity to investigate the influences of gradient, water discharge, and sediment properties (including degree of saturation) on the extent and rate of incision across a convex landform. Students should be encouraged to design their own experimental proceedings. For example, several runs might be designed to investigate the role of gradient on incision and the rate of profile adjustment. Students may be encouraged to split into groups to investigate a single variable and design an appropriate experimental procedure.
In addition to taking notes and photographically documenting their observations, discharge should be halted at select time steps throughout individual experimental runs to enable measurement of elevations across a predetermined grid. These values are tabulated for later use in generating surface maps in ArcGIS or Surfer for volumetric analysis and comparison between runs. A final write-up of the exercise, which outlines background information, experimental design, results, and conclusions, should encourage students to think about the applicability of observed trends to 'real-world' systems and the issues presented by spatial and temporal scale incompatibilities.
Determining whether students have met the goalsOrganizing group discussions and asking students to summarize their work in poster format or in the form of an oral presentation encourages evaluation of individual parts of the assignment within a larger framework. Students should have a solid understanding of the methods involved in generating the data, understand the assumptions made in doing so, and be able to reflect on their formulated hypotheses and argue for or against their rejection. Ultimately, they are encouraged to relate their findings to 'real-world' systems and understand the limitations of using a flume as an analogue.
More information about assessment tools and techniques.
URLs and References
Download teaching materials and tips
- Activity Description/Assignment: Flume Modeling Assignment (Microsoft Word 2007 (.docx) 57kB May3 10)
- Instructors Notes: Example photos and figures (Acrobat (PDF) 7.5MB May3 10)
- Solution Set:
- Flume-box materials and construction (Microsoft Word 2007 (.docx) 39kB May3 10)