Flooding in Portland, Oregon

Vanport, Oregon 1948 


Before the construction of federal dams, Portland, Oregon and other cities and towns in the Columbia River Basin were subject to severe flooding. Controlling flood waters became a priority in 1948, after Vanport, Oregon was wiped out in a late spring flood.

Vanport, on the south shore of the Columbia River across from Vancouver, Washington, was a community built quickly during World War II to provide housing for workers at the Kaiser shipyards in Vancouver and Portland. The 1948 flood lasted 20 days and killed 32 people. Another seven were reported missing and presumed dead. The community of 18,000 was destroyed.

Elsewhere in the Columbia Basin, the flood destroyed 5,000 homes, forced some 50,000 people to evacuate and caused an estimated $100 million in damage.

The U.S. Army Corps of Engineers responded to the devastation by developing a multi-use reservoir storage plan for the Columbia River Basin to reduce the impact of future floods. Later, a 1964 treaty with Canada led to the development of millions of acre-feet of water storage for flood control. This reservoir storage is used to prevent floods in the Columbia River Basin.

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Portland, Oregon 1996


In February 1996, heavy rains combined with melting snowpack caused by mild temperatures created the worst flooding in the Northwest in more than 30 years. When floodwaters threatened Portland, Oregon, dam operations reduced their impact and kept the river level lower than it would have been otherwise—one foot to one and a half feet lower. Estimates show that these measures saved the region $3.2 billion in catastrophic flood damage to homes and businesses.

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How Dams Control Floods 


Dworshak Dam

For centuries, people have built dams to help control devastating floods. During heavy rains and storms, as rivers rise, dams control floodwaters by capturing excess water in storage reservoirs. When rivers begin to drop, dam operators can slowly and safely release the stored water to the river below.

Or, the water can be stored or diverted for other uses—for generating hydropower, to irrigate farmland or to meet other needs. The flood control provided by dams prevents potential disaster and also turns the event into a future benefit.

nwrpFlood Control