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Debate kit Grade 6 Science

Beaver Dams on Hollowsett Brook: Remove Them or Leave Them?

A grade 6 science debate on whether a fictional town should pull out three beaver dams, with two-sided evidence on flooding, water temperature, oxygen, and habitat.

Objectives

  1. Students will use monitoring data to build an argument about a change to a stream ecosystem.
  2. Students will rebut an opposing claim by naming the specific evidence that weakens it.
  3. Students will explain how one physical change to a brook affects more than one population.

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.
Turbidity
Turbidity is a measure of how cloudy or murky water looks because of tiny particles floating in it. Clear water has low turbidity, and muddy water has high turbidity.
Wetland
A wetland is an area like a marsh or swamp where the ground is soaked with water for much of the year. Wetlands soak up floodwater, help clean it, and shelter many kinds of animals.
Water table
The water table is the underground level below which the ground is completely soaked with water. Dig a hole deeper than the water table and it will start filling with water.

Also: beaver dam, pond leveler

Teacher overview

This debate runs as a town board hearing across two class periods. Two teams of four argue for and against removing three beaver dams from a fictional brook, a moderator keeps time, and the rest of the class sits as the board and votes at the end. The question is genuinely open, because the same dams that flood a hayfield and warm the water also hold water through dry months and let mud settle out. One misconception worth naming before students read the evidence is that a beaver dam is simply a blockage, the way a fallen log or a clogged culvert is. A beaver pond is a small wetland with its own conditions: the water behind the dam is warmer and carries less oxygen, while the water leaving the pond is often clearer because sediment drops to the bottom. Students who treat the dams as a plumbing problem will miss the strongest arguments on both sides.

Beaver Dams on Hollowsett Brook: Remove Them or Leave Them? — Grade 6 Science
Name: ____________________________ Date: ______________

Resolution & Background

Resolution: "The town of Tarnbeck should remove the three beaver dams on Hollowsett Brook."

Hollowsett Brook runs through the fictional town of Tarnbeck. Two years ago, beavers built a dam near the town line. They have since built two more. The three ponds behind them now cover part of a hayfield and back water toward a road culvert. Everything in this kit about Tarnbeck is fictional and was written for this debate.

Some residents want the town to pull the dams out. Others want them left alone. The town board has asked for a hearing before it votes. A county biologist has offered a third idea, called a pond leveler. That is a pipe set through a dam so the pond stays at a chosen height instead of rising until it spills.

Roles. Four students argue for removal. Four argue for leaving the dams. One student moderates and keeps time. Everyone else serves as the town board, writes questions on index cards, and votes.

Format. Each team gives a three-minute opening. Teams then take five minutes to prepare. Each team gives a three-minute rebuttal, then a two-minute closing. The board asks three questions from the cards and votes. Each team writes out its opening statement and its rebuttal notes and turns them in at the end of the hearing.

Evidence File

Every reading below comes from a fictional record written for this debate, except where a source outside the scenario is named.

Case for removing the dams

  1. The ponds have backed water over about six acres of hay ground. The owner lost two cuttings of hay last summer. (Source: a fictional landowner statement written for this debate.)
  2. Ridge Road floods when the lowest pond backs water into the culvert. The road crew has cleared that culvert five times in two years and logged $2,400 in overtime. (Source: a fictional town road crew log.)
  3. In July, a volunteer team measured the brook at 15 degrees Celsius above the ponds and 22 degrees Celsius at the pond outlet. Brook trout stop feeding in water that warm. (Source: a fictional volunteer monitoring record.)
  4. The same team measured dissolved oxygen at 8.6 mg/L above the ponds and 4.2 mg/L at the pond outlet. Most fish need dissolved oxygen above 5 mg/L. (Source for the benchmark: standard water-quality guidance from EPA and USGS.)
  5. A dam that fails during a heavy storm releases the whole pond at once. The road culvert sits directly downstream of the lowest dam.

Case for leaving the dams in place

  1. Water kept moving below the lowest dam through all of last August. A brook of similar size nearby, with no dams, stopped flowing for eleven days that same month. (Source: a fictional staff gauge record.)
  2. After a July storm, the team measured 48 NTU above the ponds and 11 NTU below the lowest dam. The ponds slow the water down so mud settles instead of moving downstream. (Source: the same fictional monitoring record.)
  3. A spring survey counted four frog species and nine bird species at the ponds. A straight reach of the same brook, half a mile downstream, held one frog species and four bird species. (Source: a fictional school and volunteer survey.)
  4. Water in two shallow wells beside the ponds stood about three feet higher in August than in a well half a mile away. Neighbors on those two wells did not have to haul water. (Source: fictional well records.)
  5. Beavers rebuild. Crews that pull a dam out usually find it rebuilt within a week, so removal turns into a repeated cost rather than a one-time fix.
  6. A pond leveler would drop the water off the hay ground and away from the culvert while the pond and the wetland stay in place. (Source: a fictional county biologist memo.)

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
Use of evidence States a position with no evidence from the file Names one piece of evidence but does not explain what it shows Names at least two pieces of evidence and explains what each one shows about the brook Names several pieces of evidence, explains each, and points out which measurement matters most and why
Rebuttal Does not respond to the other team Responds in general terms without naming evidence Answers a specific opposing point using a named measurement or record Answers more than one opposing point and explains why the team's own evidence carries more weight
Reasoning about the ecosystem Treats the dams only as a structure that blocks water Mentions one effect on one living thing Connects a physical change, such as temperature or oxygen, to a change in at least one population Traces a chain from a physical change through two or more populations, and notes what the data cannot settle
Delivery and organization Hard to follow; no clear order Has an order, but transitions are unclear Follows a clear claim, evidence, and conclusion structure within the time limit Clear, well-paced, and directly responsive to the board's questions as well as the opening arguments

Differentiation

Support

Give these students an evidence card holding only the two strongest points for their side, printed in larger type, with the measurement circled. Provide rebuttal sentence frames such as "The other team said ___, but the record from ___ shows ___." Allow them to read a written opening rather than speak from notes, and let two students share one speaking role.

Extension

Ask a pair to serve as fact-checkers rather than debaters. Their job is to flag every time a speaker states something the evidence file does not actually say, and to report at the end which claims went beyond the record. A second extension is to draft the board's written decision, including the reason for the vote and one condition the board attaches.

ELL supports

Pre-teach "dam," "pond," "dissolved oxygen," "turbidity," and "water table" with a labeled cross section drawing of a brook, a dam, a pond, and a well. Provide a bilingual glossary card. Allow students to deliver their part from a written script, and give extra preparation time before the rebuttal round. Accept a labeled drawing as part of a closing statement.

Extensions

Have students find out whether their own state requires a permit before a beaver dam may be removed, using the state wildlife agency website, and report what the permit asks for. A second option is to sketch a pond leveler that would hold the Tarnbeck ponds one foot lower, label the pipe inlet and outlet, and explain in three sentences why the pipe has to be screened at the upstream end.