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Introduction How Rivers Run Stories Value Of A River What We Can Do
Connections of a River - Connectivity
Temporal disconnects (pg 3 of 3)

Temporal fragmentation occurs when human-caused forces suddenly interrupt the river's processes.

A dramatic example: the sudden dewatering of a stream segment when water is withdrawn.

The St. Louis River near Carlton, Minnesota, was typical of many large streams managed for power production. Water was diverted from the Thomson Reservoir, routed through large pipes down a steep slope to a powerhouse at Fond du Lac. There, the water powered turbines, generating electricity, and then rejoined the river.

When the river was running high, far beyond the capacity of the hydropower plant, the stretch between Thomson Reservoir and Fond du Lac appeared to be flowing normally. However, when the plant diverted nearly all the flow available to it, the river channel was almost completely dry.

Fish and other organisms that evolved to gradual rises and falls in water level suddenly confronted a complete lack of flow. Water was available only in stagnant pools. As a result, few fish lived in this section of river. Because of the licensing agreement reached with the Federal Energy Regulatory Commission in 1995, Minnesota Power now supplies minimum flows to benefit aquatic life and occasionally releases water for whitewater paddling events.

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