The Current Magazine Fall 2016 - Page 6

The Era of Dams: People Taming Nature

The era of modern dams began in the late 1800s, quickly showing that dams provide many useful services for people. They can generate hydropower, moderate river flows for flood control, and store water for agriculture and provisioning cities. Dam-created reservoirs also offer recreational opportunities, which bring economic benefits to local communities.

Unfortunately, dams always come at a dramatic environmental cost. Damming a river alters its physical structure, both upstream and down.

On the most basic level, creating an impassable barrier on a waterway prevents migratory fish like salmon and steelhead from accessing their natal spawning grounds.

Blocking a river also traps large wood and gravel essential elements for spawning and rearing fish. The result is a river channel that is scoured and structurally less complex, and thus less suitable for fish and wildlife. Finally, coastlines are deprived of regular sediment deposits, degrading beaches and other coastal habitats.

Altering the volume and pattern of water flow below a dam can also drastically reduce water quality. The higher water temperatures that result from slowed flows directly correlate to lower concentrations of dissolved oxygen, which reduces fish survivability and can even wipe out entire populations. Warmer water temperatures can also cause harmful algae blooms.

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