Project Grade 7 Engineering & Design
Ravensgill Creek Shade Structures: Cooling a Trout Reach
A five-session grade 7 build-and-test project where teams design bank shade structures on a model reach, run three timed heat trials, and combine the best features.
Objectives
- Students will build a shade structure that meets stated cost and clearance limits.
- Students will collect timed temperature data and graph it for each design round.
- Students will change one feature between rounds and justify the change from data.
- Students will combine features from two designs into a revised structure and retest it.
Vocabulary
- Dissolved oxygen
- Dissolved oxygen is the oxygen gas mixed into water that fish and other underwater animals breathe. Cold, moving water holds more oxygen than warm, still water.
Also: reach, riparian, shade credit, clearance, iteration
Teacher overview
A fictional watershed group wants to cool a cleared stretch of Ravensgill Creek where trout have stopped holding through August. Teams build shade structures over a tray-and-lamp model of the reach, run timed heating trials, and rebuild twice using their own data. The project ends with a combined design and a monitoring plan for the real bank. The misconception to address in session one is that any cover cools the water, so more cover is always better. Students who believe that will roof the whole tray and then discover that the structure blocks the channel, costs more shade credits than the group can spend, and cannot be built on the one bank the landowner allows. The design problem is to cool the water while staying inside the limits the group and the landowner have set.
Project Brief
Driving question. What shade structure can a fictional watershed group build on one bank of Ravensgill Creek to keep the water cooler on a hot afternoon?
Why this matters. Trout need cold water. Cold water also holds more dissolved oxygen than warm water, and many stream fish do poorly once dissolved oxygen falls below about 5 mg/L. When trees along a bank are cleared, the sun reaches the water all day and the reach warms.
The client. You report to a fictional volunteer group that adopts one reach of the creek. The group has permission to work on one bank only.
The model you will test. A shallow tray of water stands in for the reach. A clip lamp stands in for the afternoon sun. Your structure must shade the tray without touching the water.
The limits. These are fixed. A design that breaks one is not scored.
- Your structure may use no more than 12 shade credits. Cardboard costs 3 credits a piece, mesh 2, burlap 2, slats 1, craft sticks 1, and string is free.
- The structure may stand on one long side of the tray only. Nothing may rest on the far bank.
- At least 4 centimeters of clearance must stay between the structure and the water surface.
- The structure must survive a high-flow test, which is one cup of water poured into the tray from a height of 20 centimeters. Switch off and unplug the lamp before this pour.
- Build time is 20 minutes per round.
The criteria. These are scored, and a design earns more points the better it does on each.
- The drop in water temperature compared with a bare tray after 20 minutes under the lamp.
- How little the structure costs in shade credits.
- How much of the channel stays open to view from above, which matters for the group's stream survey.
What you turn in. Your team submits four things.
- The final structure, built and labeled.
- A data table and a line graph showing temperature over time for all four rounds.
- A one-page design report naming what you changed between rounds and why.
- A monitoring plan for the real bank. Name what to measure, where, when, and for how long.
Milestones
Session 1. Set up and get a baseline. Read the brief. Set up the tray and lamp, keeping the cord and the fixture clear of the water and letting the bulb cool before anyone moves it. Run a bare tray for 20 minutes. Record the water temperature every 4 minutes. This is your baseline. Turn in the baseline table.
Session 2. Round one build and test. Build your first structure in 20 minutes. Count your shade credits. Check clearance with a ruler. Run the same 20-minute test and record the same way. Turn in the credit count and the round-one table.
Session 3. Round two, change one thing. Study your round-one graph. Change exactly one feature. It might be the material, the height, the angle, or the width. Write down what you changed and what you expect. Rebuild, retest, record. Turn in the change note and the round-two table.
Session 4. Combine with another team. Trade data tables with a partner team and read their numbers against your own. Decide which single feature of their structure outperformed anything in yours, and which feature of yours their data cannot match. Build a structure that carries both, then test it under the same lamp and the same timing. Turn in a short table showing the two features you borrowed and what each contributed.
Session 5. Report and pitch. Graph all four rounds on one set of axes. Write the design report. Write the monitoring plan for the real bank. Present for four minutes and take two questions. Turn in the structure, the graph, the report, and the plan.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Rubric
| Criterion | 4, exceeds | 3, meets | 2, approaching | 1, beginning |
|---|---|---|---|---|
| Build within limits | Every round stays inside the credit, bank, clearance, and flow limits, and the credit count is shown for each | The final structure meets all four limits and the credit count is shown | One limit is broken in one round and corrected later | A limit is broken in the final build |
| Data collection | All four rounds are recorded at the same intervals with units, and the graph shows all rounds on shared axes | All four rounds are recorded with units and graphed | Some rounds are missing readings or units | Data is incomplete or unlabeled |
| Reasoning between rounds | Each change names the data that prompted it and states a prediction that is later checked | Each change is named and tied to the previous round's result | Changes are named without reference to the data | Changes appear to be random |
| Combining features | Both borrowed features are named, their sources credited, and the report says what each contributed to the result | Two features are borrowed and the combined design is tested | One feature is borrowed or the combined design is not tested | No combination is attempted |
| Monitoring plan | The plan names the measurement, the spot, the time of day, the frequency, and how long the group should keep it up | The plan names a measurement, a spot, and a frequency | The plan names a measurement only | No monitoring plan |
Differentiation
Support
Give these teams a starter frame of two craft sticks and a string already assembled so building time goes into the shading surface rather than the structure. Provide a printed data table with the time column filled in at 4-minute marks. Offer a menu of three changes to choose from in session three instead of an open choice.
Extension
Ask these teams to test whether the structure's angle matters more than its material by holding one constant across two extra trials. Have them estimate, using their own graph, how long the lamp would need to run before the shaded tray reached the temperature the bare tray hit at 20 minutes, and explain why that estimate is rough.
ELL supports
Pre-teach reach, bank, and clearance with a labeled sketch of a stream cross section showing both banks, the water, and a structure above it. Provide the frames "We changed ____ because round ____ showed ____" and "We borrowed ____ from ____ because ____." Allow the design report to be delivered as a labeled poster with short captions.
Extensions
Have teams price their final structure as if it were built full size on the real bank, using a stated cost per square foot the class agrees on, and then compare that figure with the cost of planting willow stakes that would take six years to shade the same reach. Ask each team to recommend one, both, or neither to the fictional group, and to say what they would measure after five years to find out whether the choice was right.