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Lesson plan Grade 7 Science

Quill Weir Fish Passage: Comparing Three Design Options

A grade 7 lesson in which students score three fish passage options at a fictional mill weir on percent of trout passing, cost per fish, and the town's water intake.

Objectives

  1. Students will calculate the percent of tagged trout passing under each design option.
  2. Students will compute the cost per fish passed and compare the three options.
  3. Students will defend a recommendation using both biodiversity evidence and water supply evidence.

Vocabulary

Weir
A weir is a low wall that water flows over, used to control water levels and to measure flow. The deeper the water pouring over the weir, the more water is flowing.

Also: fishway, ecosystem service, criteria, trade-off

Teacher overview

A weir is a low dam built across a river, and thousands of them remain in place long after the mills they served closed. This lesson puts students in the fictional town of Quillmoor, where the Quill Weir blocks trout from reaching spawning gravel upstream while the pond behind it holds the town's summer water intake. Students compare a rock ramp fishway, a vertical slot fishway, and full removal of the weir using tagged-fish results, costs, and the effect on the intake. Teaching note: students often assume a fish ladder lets every fish through, and that a structure either works or does not. Passage rates in this scenario differ by design, and the class has to decide how much better passage is worth when the town also depends on the pond.

Procedure

Hook (5 min): Project or sketch a cross-section of the Quill Weir in the town of Quillmoor: a stone wall 9 feet high across the Ashlin River, with a pond behind it and riffles below. Ask students what a trout swimming upstream would do when it reaches the wall, and record two or three predictions on the board.

Background and data (10 min): Explain that biologists tagged 200 trout below the weir and counted how many passed above it during a test of each option. Distribute the handout and read the table together. Point out the last column, which tells whether the mill pond that holds the town's summer intake would still exist under each option.

Model one calculation (8 min): Work handout item 1 with the class, showing 150 divided by 200 equals 0.75, which is 75 percent. Then model item 5 without finishing it: cost divided by the number of fish passing gives a cost per fish. Ask for a thumbs up or down on whether the class is ready to continue. If more than five students signal down, work item 2 together before releasing groups.

Group work (18 min): Students work in pairs through handout items 1 through 8, recording the percent passing and the cost per fish for each option. Circulate and check that pairs are dividing cost by fish passed rather than fish passed by cost, which is the most common error in this task.

Scoring and recommendation (8 min): Bring the class back together and build the scoring table from handout item 9 on the board, one option at a time. Ask two pairs with different totals to explain their reasoning before students write their recommendation for item 10.

Debrief and exit ticket (6 min): Ask the class what Quillmoor would give up under Option C and what it would gain. Collect item 10 as an exit ticket, and look for recommendations that cite one number about trout and one about the town's water.

Quill Weir Fish Passage: Comparing Three Design Options — Grade 7 Science
Name: ____________________________ Date: ______________

Student Handout

The town of Quillmoor is deciding what to do about the Quill Weir on the Ashlin River. Biologists released 200 tagged trout below the weir and counted how many reached the gravel upstream during a test of each option. All costs and counts below are part of this scenario.

Option Cost Tagged trout passing, out of 200 Mill pond kept?
A. Rock ramp fishway $420,000 150 Yes
B. Vertical slot fishway $630,000 180 Yes
C. Remove the weir $294,000 196 No
  1. What percent of the 200 tagged trout passed the weir under Option A?
  2. What percent of the 200 tagged trout passed under Option B?
  3. What percent of the 200 tagged trout passed under Option C?
  4. How many more trout passed under Option B than under Option A?
  5. What is the cost per trout passed under Option A? Divide the cost by the number of trout that passed.
  6. What is the cost per trout passed under Option B?
  7. What is the cost per trout passed under Option C?
  8. Which option moves the most trout for each dollar spent?
  9. Score each option twice. For trout passage, give 3 points to the option with the most trout, 2 to the next, and 1 to the fewest. For water supply, give 3 points if the mill pond stays and 1 point if it is removed. Which option has the highest total score?
  10. Recommend one option to the Quillmoor town council. Cite one piece of evidence about trout and one about the town's water supply.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

These items key the numbered questions on the student handout, in the same order.

  1. Answer: 75 percent.
    150 trout divided by 200 tagged trout equals 0.75, or 75 percent.
  2. Answer: 90 percent.
    180 divided by 200 equals 0.90, or 90 percent.
  3. Answer: 98 percent.
    196 divided by 200 equals 0.98, or 98 percent.
  4. Answer: 30 trout.
    180 trout minus 150 trout equals 30 more trout under Option B.
  5. Answer: $2,800 per trout.
    $420,000 divided by 150 trout equals $2,800 for each trout that passed.
  6. Answer: $3,500 per trout.
    $630,000 divided by 180 trout equals $3,500 for each trout that passed.
  7. Answer: $1,500 per trout.
    $294,000 divided by 196 trout equals $1,500 for each trout that passed.
  8. Answer: Option C.
    At $1,500 per trout passed, removal costs the least for each fish moved, compared with $2,800 under Option A and $3,500 under Option B.
  9. Answer: Option B, with 5 points.
    Option A scores 1 point for passage plus 3 for water supply, which is 4. Option B scores 2 plus 3, which is 5. Option C scores 3 plus 1, which is 4.
  10. Answer: Accept any option defended with one trout number and one water supply point.
    A strong Option B answer notes that 90 percent of tagged trout passed while the pond that holds the town's intake stays in place. A strong Option C answer notes that 98 percent passed at the lowest cost per fish, and proposes a new intake to replace the pond.

Differentiation

Support

Give these students a version of the Quillmoor table with the percents for items 1 through 3 already filled in so they start at item 5, and provide a sentence frame for item 10: "I recommend Option ___ because ___ trout passed and because the town's water supply would ___."

Extension

Ask students to calculate how much the town of Quillmoor would pay for each additional trout passed when moving from Option A to Option B, then write a short paragraph on whether that added cost is worth it.

ELL supports

Preteach weir, fishway, and pond with a labeled cross-section drawing of the Ashlin River. Allow students to give their item 10 recommendation orally to a partner before writing, using the sentence frame from the Support section.

Extensions

Students can research whether any dam or weir on a river near their community has a fishway or has been removed, then compare that decision with the trade-offs the town of Quillmoor faced.