Freeing the Elwha (The Impacts of Hydroelectric Dams on Salmon)
OverviewDams are important to people but they have a serious impact on salmon migration. How do dams affect salmon and what successes have people had in trying to help salmon migration?
This lesson focuses on the impacts that hydroelectric dams have had on anadromous salmon migration and some of the mitigation techniques that have been designed to reduce these impacts. Hydroelectric projects were started during the Great Depression and continued through the 1960's and 1970's for the purpose of channeling water for irrigation in the arid Columbia Basin and to generate cheap electricity. However, the dams created obstructions for migrating salmon. Even those dams built with fish passage, such as fish ladders and navigation canals, have had major impacts on the survivorship of juvenile salmon due to mortality in the turbines and spillways, increased water temperatures, predation, and a myriad of other factors.
- Fish Ladder- A series of stepped waterfalls which bypass the dam, descending from the reservoir to the riverbed below the dam, designed to allow migrating fish to pass the dam structure.
- Penstock- A intake tube for channeling water through the turbines of a dam or via spillways and floodgates.
- Reservoir- A man-made water containment system often the result of lake filling behind a dam, but also can be water stored in large tanks or underground storage.
- Navigation Canal- A series of locks used to allow boat traffic to bypass the dam. They typically contain mechanisms for raising or lowering water levels to enter and leave reservoirs.
- Turbine- A rotating device surrounded by magnets, which is spun by the pressure of flowing water for the purpose of generating electricity.
- Barging- A technique to assist juvenile salmon migrating past the dams by loading them on a barge and sailing them downriver, so as to reduce the mortality related to passing through turbines, falling over spillways, or being eaten by predators. This technique is controversial and the success remains unclear.
- Lesson 14- Impact of Dams on Salmon.pptx
- Dam Site Selection.pptx
- Dam Site Selection.pdf
- Reflection Journal Pages (printable handout)
- Vocabulary Notes (printable handouts)
Review Essential Question; introduce Guiding Question.
Students should take a few minutes to respond to the first reflection prompts. Discuss their answers and any questions they've generated.