Project - Sediment Study
In this culminating project, students go out into the field and test their theories about erosion and sedimentation at a local creek. How are sediments distributed along the creek? Does ...
In this culminating project, students go out into the field and test their theories about erosion and sedimentation at a local creek. How are sediments distributed along the creek? Does it vary by location (the source, mid-stream, and the mouth)? Does it vary by the velocity of the current? Different classes can collect information for the different study areas. At a study site, they will draw maps, measure the velocity of the current, and collect sediment samples from the creek bed. These samples are analysed back in the classroom for the percent of different sediments they contain. Finally, students stand back and examine their data to try to make sense of the sediments they find. If it is not possible to bring students to a creek, there are many ways to bring the data to them. Collect the sediment samples yourself with photos and water velocity information OR use the Suspended Sediment Database to draw your conclusions. This USGS database provides stream flow and sediment information for over 1,500 rivers and creeks nationwide (see the Going Further section for more information on using the USGS’s database).
Students collecting data at the creek.
Can describe the major types of sediment.
Can explain how sediment size and current velocity affects deposition.
Can create a hypothesis and make predictions of what to expect from experimental data based on prior knowledge.
Can make observations and record data in a science lab notebook.
Can use their own observations and data draw logical conclusions.
Sediment Study - Logistics
Day 1: Experimentation (may be split into two days)
20 min describe the question and experiment and have students make hypotheses and predictions
5 min describe experiment procedures
30-45 min conduct experiment and collect sediment samples at the study site
travel time to the study site and back will vary
Day 2: Soil Separation Tests
10-15 min set up soil separation tests
Day 3: Data Analysis and Summary
15-20 min analyze soil separation test results
10 min summarize group results and display
Day 4: Drawing Conclusions
45-50 min discuss results and draw conclusions
Teams of 3 students
For sediment study, each group of students needs: (I assembled all the materials into several shoebox-sized plastic containers to become our class set of “creek kits”. Many of these items are the same as those needed for the Habitat Survey lesson.)
- Copy of Sediment Study directions
- 2-3 white paper towels
- 1 extra-large spoon or small hand trowel
- 1 hand lens or magnifying glass
- 4 meter length of string tied into a knot every 1 meter (brightly colored polyester contractor’s string works well)
- 2 bamboo skewers to stake out the string
- 1 12 inch plastic ruler
- 1 stopwatch or timer
- 5 film canisters for collecting sediment samples
- 1 Sharpie marker
- Labelling dots or masking tape
- Latex gloves or yellow dishwashers’ gloves
For the sediment study, the teacher needs:
- Topographic map of the creek they will be studying, assuming you will be studying sediments at the creek in the school’s watershed, you should have a copy of this map from the Topo Tour lesson
- first aid kit
- extra film canisters
- extra copies of the Sediment Study directions
- field guides of local plants and insects
- optional: water and paper cups
For classroom tests and interpretation each group needs:
- 1 copy of the Data Summary Sheet
- 3 clear 15 ml tubes with lids, glass or plastic
For classroom tests and interpretation the whole class can share:
- 2 tablespoons
- 2 rulers
- 1 small jar alum (available at supermarkets for pickling)
- 1 package removable dot labels or rolls of masking tape
- several Sharpie markers
Day 1 – Creek. Pick 3 study sites at different places along the creek. Make sure that the sediment makeup at each of the 3 sites is very distinct. I chose a pond at the source of our creek with mucky clay and silt above a layer of sand, a fast flowing area midstream with weathered river rocks and gravel, and a wide man-made channel near the mouth with a mixture of sediments.
Day 2-4 – Classroom.
Sediment Study - Background
See Erosion Patterns Background for information about erosion and typical sediment deposition patterns.
In this project, I wanted students to grapple with the notion that science is rarely as simple as the textbooks. Usually, in a river, stream or creek bed, a fast-flowing midstream section will have lots of gravel and larger rocks and the mouth will have lots of silt and clay as the current slows. Usually, the riverbed at source will have whatever type of soil the surrounding hillsides are made of. However, in real life, things are rarely so simple. There are culverts that direct creeks underground, man-made concrete channels, and dams. There are polluters, dogs and gardeners to contend with, all of whom affect the types of sediments one will find in any given spot in an urban creek.
The beauty of this project is that the ability of fast-moving water to carry more sediment of larger sizes is so robust that irrespective of the other variations, if there is sediment at all to be observed, it will almost certainly follow this trend. Most importantly, students are able to look for patterns in real world data and consolidating everything they have learned about watersheds and erosion. Surprises come from changing students’ expectations of what a creek looks like at different places and from discovering the variability of data, even at a single study site.
In this project, different classes of students go to one of 3 sediment study sites to collect information. Students lay out a 4 meter transect line to create 5 imaginary lines stretching across the creek. Students do the following:
- Draw a careful map of their study area
- Measure the current velocity in meters/second
- Approximate the width of the creek
- Measure the depth of the creek 30 cm (approximately 1 foot) from the shore at each of their 5 imaginary lines
- Collect a sediment sample from each of their 5 imaginary lines approximately 30 cm out from shore
Sediment Study - Getting Ready
For sediment study at the creek:
- Contact the proper authorities/property owners/neighbors to obtain permission to bring your students to your chosen survey site.
- Copy Sediment Study Directions.
- Prepare “creek kits” with: paper towels, spoon or small hand trowel, hand lens or magnifying glass, 4 meter length of string tied into a knot every 1 meter, skewers, ruler, timer, film canisters, Sharpie marker, masking tape, and gloves
- Prepare teacher bag.
- Arrange transportation to and from the survey site.
- Display the topographic map showing the creek you will be studying.
For classroom analysis:
- Prepare soil separation station with: 15 ml tubes, alum, ruler, labels, spoons, and directions
- Copy Data Summary Sheets for students to summarize their data and post for everyone to view.
- On a bulletin board, wall, or at the top of the front whiteboard/chalkboard, create 3 areas for students to post their Data Summary Sheets.
Sediment Study - Lesson Plan
Day 1: Experimentation
- Before leaving the classroom, introduce the project by posing the following questions to students:
- How are sediments distributed along a river or creek?
- Does it vary by location (the source, mid-stream, and the mouth)?
- Does it vary by the velocity of the current?
- What other factors might affect the distribution of sediments and why?
- On the front board, create a list of factors that students believe would affect the distribution of sediments.
- Tell students that they will be analyzing sediment samples from different parts of the creek in the school’s watershed. They will be making observations of the sediments at different places along the creek and will be looking for the reasons that sediments have been deposited in those ways.
- Point out the 3 sediment study sites on the topographic map of the creek. Assuming you will be studying the creek in the school’s watershed, students should already be very familiar with this map from the Topo Tour lesson. Ask students to point out the geographical differences between the 3 sites. Which site is at the highest elevation? Which site is steepest? Is any in a valley, on a flat plain, on a hillside, etc?
- Have students open their lab notebooks and set up a new page with the title of the study, the date, etc. Have students write down the question: “How are sediments distributed along the creek in our watershed? If the sediments are different from place to place, what causes the variability?”
- Have students make hypotheses about what to expect. I find that if you give students fill-in-the-blank style statements, I get much better hypotheses than if they are just told to make some predictions about what they might expect at each of the study sites and explain why. I used the following fill-in-the-blank style statements:
- I think ______ are the most important factors that influence the way sediments are distributed along a creek.
- At the first study site near the source I would expect to find _______, because ______.
- At the second study site mid-stream I would expect to find _______, because ______.
- At the third study site near the mouth I would expect to find _______, because ______.
- If you are dividing Day 1 into 2 class periods, stop here and continue the following day with Step 7.
- When students finish writing down their hypotheses, distribute the Sediment Study Directions and describe the experiment procedures that will be completed at the creek. Tell students what teams they will be working with and how to find a study site (you can assign them there or they may find their own site). Show them how to stake out their survey site with the string and stakes.
- Depart for the trip.
- When you arrive, make sure that each team has an appropriate survey site and a creek kit. Make sure that groups are setting up their string and stakes correctly.
- Allow students to get started immediately collecting the information in their lab notebooks. Circulate among groups to help students who have questions.
- Teams that finish early can sit quietly with a field guide and try to identify the plants and animals they found.
- When all groups are finished, return to the classroom.
Day 2: Soil Separation Tests
- Tell students to get out their soil samples. Tell them to set up a soil separation test with the sediment collected at their site, making sure to label each container with their team name, the sample number, and the location where it was collected.
Day 3: Data Analysis and Summary
- Allow students 10-15 minutes to interpret soil separation tests and clean up those stations. For each sample, they should draw a picture of the separation test in their lab notebook, labeling each layer with what the layer is made of (gravel, sand, silt or organic material) and the height of that layer in millimeters.
- Have students create a table like the one below in their lab notebook:
|| Line 1
- Show students how to use this table to average the results from their 5 sediment samples and then turn the average heights into a percent.
- This information, along with the other data can be entered on the Data Summary Sheets and posted below one of the 3 site headings around the room.
Day 4: Drawing Conclusions
- Remind students of the questions posed at the beginning of this activity. Allow them to spend a moment rereading the hypotheses they made at the beginning of the project.
- The remainder of this class period will vary according to the data your students collected and the conclusions that may be drawn from this data. The general idea is to have the students devise a way to summarize the data collected at each of the study sites and then look for patterns. I spent 20-30 minutes simply creating tables and charts with my students – tables of width and depth measurements, tables of current speed, tables of sediment composition, bar graphs for the more interesting types of data. I found that starting by comparing the width and depth measurements enabled students to imagine what each of the areas looked like – a pond, a small stream, a wide channel. Adding the current velocity information confirmed their suspicions of how quickly the water moved at each site. Finally, once they have had experience averaging the previous data, the most complicated task of interpreting the sediment composition data is more accessible than if we had tackled that first, even though that is the whole point of the exercise. Some issues that are interesting to explore:
- Was there variability within the 5 sediment samples collected by a single team? Why is it important to collect 5 samples instead of just 1?
- Was there variability among the data collected by the different teams at a single study site along the creek? What might have caused those differences?
- What patterns in sediment distribution were found at each of the 3 study sites?
- What factors (width, depth, current velocity, others) may have caused the variation in sediment distribution? Why do you feel this factor is important?
Sediment Study - Going Further
- The USGS has compiled a Suspended Sediment Database describing the distribution of suspended sediments across the United States. The database has answers to the questions for over 1,500 rivers and creeks across the United States: How much water is flowing in my river? How much sediment is suspended in the water? How much of this sediment is discharged and where? Information is collected daily over a period of years so your students can graph and plot data correlating stream flow to sediment load and deposition. The data is pretty daunting (pages and pages of numbers with complicated units of measure such as “daily mean suspended-sediment concentration in milligrams per liter”) so for use with students, it is best to cull the data down to a much smaller subset. For instance, if you wish to draw attention to yearly cycles in water flow, pick one day a month over 2 years. Have the students graph that information then look for patterns.
- Did the Suspended Sediment Database not have everything you are looking for? Try the NWIS Database instead. This mind-boggling resource provides information about the amount of water, the water quality, water distribution, and the movement of both surface and underground water at 1.5 million monitoring sites across the country. Again, you can select a subset of this data for students to draw conclusions from.
Sediment Study - Standards
Shaping Earth’s Surface
2. Topography is reshaped by the weathering of rock and soil and by the transportation and deposition of sediment. As a basis for understanding this concept:
a. Students know water running downhill is the dominant process in shaping the landscape, including California’s landscape.
b. Students know rivers and streams are dynamic systems that erode, transport sediment, change course, and flood their banks in natural and recurring patterns.
c. Students know beaches are dynamic systems in which the sand is supplied by rivers and moved along the coast by the action of waves.
Investigation and Experimentation
7. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other three strands, students should develop their own questions and perform investigations.