Thurlow Bend Dam: Remove It or Relicense It

Resolution: The Marrick River Power Authority should remove Thurlow Bend Dam rather than relicense it with a fish passage retrofit.

Background. Thurlow Bend Dam is a fictional structure on the fictional Marrick River, and every figure in this kit is invented for the debate. The dam was completed in 1947. It stands 84 feet high, holds a reservoir eleven miles long, and its powerhouse produces about 11 megawatts, enough for roughly 6,400 homes in the region it serves. Its federal operating license expires in four years, and the authority must choose one of two paths before then.

The removal path takes the dam out over two summers, reopens 46 miles of the Marrick and its tributaries to migrating fish, and replaces the lost generation by purchasing power from the regional grid. The relicensing path keeps the dam for another 40 years and adds a fish ladder for adults moving upstream, a screened surface bypass for juveniles moving downstream, and rebuilt turbines that pass more water for the same output.

Both paths are lawful, both have been chosen at comparable dams, and each carries substantial costs.

Roles. Each team of four assigns one speaker to the opening case, one to the sediment and water-quality line of argument, one to the energy and community line, and one to rebuttal. The judging panel uses the rubric below and must record the specific evidence that moved them. A moderator, either the teacher or a student, keeps time: four minutes for each opening, three minutes for each of two exchanges, and two minutes for each closing. Each speaker drafts a written case or rebuttal brief on the index cards before the round and turns it in with the debate, so the argument can be scored on paper as well as aloud.

Every figure below is invented for the fictional Marrick River scenario. Sources are named so that students learn to say where a claim comes from, and fictional sources are labeled as such.

Case for removing the dam

1. Sediment starvation below the dam. The reservoir traps nearly all of the sand and gravel the river carries. Surveys by the fictional Marrick River Monitoring Program found that the bed for twelve miles below the dam is now armored, meaning the fine material is gone and only large cobble remains. Spawning fish need loose gravel to build nests, and that gravel is no longer being resupplied.
2. Warmer summer water. The reservoir spreads the river into a wide, slow pool that absorbs sunlight. The same monitoring program recorded August water temperatures below the dam averaging 6 degrees Celsius warmer than at a free-flowing reach upstream of the reservoir.
3. Low oxygen in late-summer releases. The reservoir separates into layers in summer, and the powerhouse intake draws a mix of warm surface water and oxygen-poor water from the layer just below it. Releases in August have measured 3.2 mg/L of dissolved oxygen. Most fish need dissolved oxygen above 5 mg/L, a standard water-quality benchmark, so the release itself stresses the reach below.
4. Ladders move adults, not juveniles. The fictional regional fisheries commission reports that ladders at comparable dams pass most returning adults, while young fish moving downstream must pass through or around the turbines. Entrainment losses accumulate, and a fish that survives one passage may not survive several.
5. Aging structure. The authority's own engineers estimate $14 million in spillway and gate repairs during the next license period, separate from the cost of the passage retrofit.
6. Reopened habitat. Removal restores access to 46 miles of cool tributary water that migrating fish have not reached since 1947.

Case for relicensing with fish passage

1. Carbon-free generation that can be dispatched. The powerhouse produces about 11 megawatts on demand, including on winter evenings when solar output is zero. The fictional regional grid operator states that replacement power for this authority would come mainly from a natural gas plant, so removal raises regional emissions until new clean generation is built.
2. A large sediment pulse during removal. The reservoir holds decades of accumulated sediment. Modeling by the fictional Marrick River Monitoring Program projects that turbidity below the site would stay elevated for two to four years after removal, smothering some of the same gravel beds the project aims to restore.
3. The reservoir is a working water supply. Two towns draw their drinking water from the reservoir, and the fire district refills its tankers there. Removal would require new intakes on a free-flowing river that runs low in August.
4. Drought flow support. The authority holds water in spring and releases it through the summer. During the last dry summer, releases kept the reach below the dam at 210 cubic feet per second when the unregulated tributary above the reservoir fell to 30 cubic feet per second.
5. Passage technology has improved. Screened surface bypasses collect young fish before they reach the turbines. The fictional fisheries commission reports downstream survival above 90 percent at two comparable retrofits, a figure that passage through the turbines without a bypass never reached.
6. Cost and local revenue. Removal is estimated at $27 million, and the authority would lose the generation revenue that currently keeps its rates below the regional average.

Shared background both sides may use. The dam is one of four on the Marrick. Removing Thurlow Bend alone would not reopen the whole river, and the other three licenses expire over the following fifteen years.