Debate kit Grade 7 Science
Should the Ashkirk Mill Dam Come Out of the Elderbeck River?
A two-session grade 7 science debate comparing dam removal, a fish ladder, and repair at a fictional mill dam, with evidence on fish, sediment, safety, and town use.
Objectives
- Students will compare three design options for an aging dam against stated ecological and community criteria.
- Students will support a position on dam removal with evidence drawn from a shared file.
- Students will explain how a dam changes fish movement, water temperature, and sediment downstream.
Vocabulary
- Dam
- A strong wall built across a river to hold back water. Dams store water for people and farms, help prevent floods, and can make electricity.
- Fish ladder
- A series of water steps built beside a dam so migrating fish, like salmon, can swim past it. Fish leap or swim from pool to pool to reach the river above.
- 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: impoundment, sediment, dry hydrant
Teacher overview
This kit runs as a two-team structured debate across two sessions, with research and preparation first and four timed rounds second. The question facing the fictional village of Ashkirk is what to do with a small, aging mill dam that no longer runs a mill. Removing a dam reopens a river to fish and sediment, yet the pond behind this one is used by the community and holds mud that would have to be handled first, which is why towns facing this choice reach different conclusions.
Resolution & Background
Resolution: The Ashkirk Mill Dam should be removed and the Elderbeck River returned to a free-flowing channel.
Background: Ashkirk, the Elderbeck River, and every number below are fictional and were written for this debate. The Ashkirk Mill Dam is 12 feet high and about 140 years old. It was built to turn a grain mill. The mill closed long ago. The dam still holds back a pond of about 9 acres.
A state inspection last year rated the dam in poor condition. The state gave the village three choices. The first is removal, which takes out the dam and lets the river run in its old channel. The second is a fish ladder, which is a set of stepped pools that lets fish climb past the dam while the pond stays. The third is repair, which rebuilds the dam face and spillway and leaves everything else as it is.
Each choice changes the river in a different way. A dam blocks fish that swim upstream to spawn. A pond spreads the water out and makes it shallow, so summer sun warms it. Warm water holds less oxygen than cold water, and most fish need dissolved oxygen above 5 mg/L. A dam also traps sand and silt that the river used to carry downstream, and gravel beds below a dam can lose the fresh material that fish eggs need.
The pond matters to people too. Neighbors skate on it in winter and launch canoes in summer. The fire department draws water from it through a dry hydrant. The old mill and its pond are listed on the village historic register.
Roles: Teams of four take these roles. The opening speaker states the claim and two reasons. The evidence lead presents three pieces of evidence. The rebuttal speaker answers the other team's strongest point. The closing speaker explains why the team's evidence carries more weight. One student moderates and keeps time, and the rest of the class judges with the rubric.
Evidence File
Case for removing the dam
- Fish cannot get past it. A fictional survey done for this debate counted river herring at four sites. Crews found herring at both sites below the dam and none at either site above it. The nearest spawning gravel sits 3 miles upstream. (Illustrative survey written for this debate.)
- The pond loses oxygen in summer. Monitoring written for this debate recorded 4.2 mg/L of dissolved oxygen at the pond outlet on August afternoons. The free-flowing reach above the pond stayed at 7.8 mg/L on the same days. Most fish need oxygen above 5 mg/L. (Illustrative monitoring for this debate; the 5 mg/L benchmark comes from standard EPA and USGS guidance.)
- Repair costs keep coming. A fictional state dam safety engineer estimates that repairing the face and spillway would be followed by inspections and maintenance for as long as the dam stands, while removal is paid for once.
- Gravel returns downstream. With the dam gone, the river again carries sand and gravel to the reach below, rebuilding the clean beds that trout and herring use for eggs.
Case against removing the dam
- The sediment behind the dam is not clean. Testing written for this debate found metals from the old mill in the pond mud. Releasing that mud downstream could harm the river below, so it would have to be dug out and hauled away first, which is slow and expensive. (Illustrative testing written for this debate.)
- The village loses a working water source. The fire department's dry hydrant draws from the pond. A fictional Ashkirk fire chief states that without the pond, tanker trucks would have to haul water to fires on the north side of the village, adding minutes to every response.
- A fish ladder solves the fish problem without erasing the pond. The state's second option lets herring climb past the dam. A fictional fisheries biologist notes that ladders work better for some species than others, yet a working ladder plus the pond may satisfy both goals at once.
- The pond is part of the village's history and its winter recreation. Removal ends skating and canoeing on the pond and changes a landscape listed on the historic register, which the community would have to agree to give up.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Rubric
| Criterion | Emerging | Developing | Proficient | Advanced |
|---|---|---|---|---|
| Evidence use | Asserts a position with no evidence from the file | Cites one piece of evidence without linking it to the claim | Cites at least two pieces and explains how each supports the claim | Cites several pieces, explains each, and shows why they outweigh the opposing evidence |
| Comparing solutions | Discusses only one option | Names a second option but does not compare it | Compares removal with at least one other option against stated criteria | Compares all three options and names the tradeoff each one accepts |
| Rebuttal quality | Does not answer the other team | Answers with opinion rather than evidence | Answers a specific opposing point using file evidence | Answers several points and identifies the assumption each one rests on |
| Organization and delivery | Difficult to follow | Structure present but transitions unclear | Clear claim, evidence, and conclusion in order | Clear, well-paced, and directly responsive to the resolution throughout |
Differentiation
Support
Provide a one-page option chart with three columns labeled Removal, Fish ladder, and Repair, and let students mark which evidence points belong under each. Give the rebuttal speaker sentence starters: "The other team said ___, but our file shows ___."
Extension
Ask students to write a fourth option the village could put on the table, such as removal paired with a new fire department water tank, and to defend it against the strongest point from each original side.
ELL supports
Pre-teach "dam," "pond," "sediment," and "spawn" with a labeled side-view drawing of a river, a dam, and the pond behind it. Provide a two-column note sheet headed "Reasons to remove" and "Reasons to keep" so students can sort evidence as it is presented.
Extensions
Have students research one dam near their own community using a state dam inventory, note its height, age, and current purpose, and write a paragraph predicting which of the three options that dam's owners are most likely to choose.