Floods shaped much
of the modern Columbia River’s course. Regular annual cycles of flooding in
spring and early summer influenced the anadromous life history of Columbia
basin salmon and steelhead. Floods scoured away the topsoil and loser layers of
rock, created the channel of the modern river and exposed the solid basalt that
is the foundation for many Columbia River dams.
multiple floods that carved the river’s course between modern-day eastern
Washington and the Pacific Ocean occurred between 12,800 and 15,000 years ago,
at the end of the last ice age. The Cordilleran ice sheet covered the Pacific
Northwest at the time, extending as far south as the Puget Sound area, the
southern reaches of the Okanagon River and the Columbia River valley in north
central Washington, northern Idaho and northwestern Montana. There, in
northwestern Montana, an impoundment known as glacial Lake Missoula repeatedly
undermined the 2,500-foot-tall ice dam that held it back. The ice dam was on the
Clark Fork River east of Lake Pend Oreille and
near present-day Missoula.
resulting floods — there were more than 100 — coursed through northern Idaho,
eastern Washington and the Columbia River Gorge, carving the Grand Coulee and
the Big Bend and scouring the Columbia River Gorge to its underlying basalt.
Today these are known collectively as the Bretz Floods, for J. Harlan Bretz,
the geologist who first described them in 1919.
in the Gorge reached 700 to 900 feet deep. Water in modern-day Portland,
Oregon, more than 500 miles downstream, was 400 feet deep. Mineral deposits
were carried from western Montana to the lower Columbia River. According to
geologist and author John Elliot Allen, these were the greatest scientifically
documented floods known to have occurred in North America, inundating nearly
16,000 square miles in places up to several hundred feet deep. Allen estimates
that during the floods the Columbia carried ten times the flow of all the
rivers in the world today and 60 times the flow of the modern Amazon River. The
floods scoured more than 50 cubic miles of silt and sediment from the
Columbia Plateau, leaving the network of scabland channels and bare
basalt surfaces that are evident today. Flood waters extended to the southern
extreme of the Willamette Valley at Eugene.
among the many catastrophic events that shaped the modern Northwest, helped
shape the unique life history of salmon, as well. Over time, salmon adapted to
changes in climate and the physical environment. During the last ice age,
Pacific Northwest salmon probably populated rivers as far south as California.
Repeated floods altered their habitat, and the warmer climate that followed the
retreat of the ice probably caused salmon to abandoned the warmer, more
southern rivers and move north again.
the modern Columbia River Basin took shape, salmon adapted their journey to the
ocean to coincide with the annual snowmelt freshet in the spring and early
summer. The rushing water provided the fastest possible journey from the
freshwater spawning habitat to the estuary, where the fish undergo
physiological changes to adapt to salt water before spending most of their
adult lives in the ocean.
Columbia River annually pours an average of 180-190 million acre-feet of water
into the Pacific Ocean, the fourth-highest volume of all rivers in North
America. With the bulk of the runoff coming in the spring and early summer when
snow melts in the many mountain ranges of the Columbia River Basin, the river
quickly can become a raging torrent, rise by a matter of feet overnight and
stay bank-full or beyond for days. Winter floods can occur, as well, when warm,
wet weather systems move in from the Pacific and override or clear out the
colder air of the interior basin, and rain falls on snow.
its huge annual runoff, the Columbia does not have a history of catastrophic
flooding like the Missouri or Mississippi. There were major floods in 1876,
1894, 1948 and 1964, but before the construction of dams in most years
the Columbia simply rose in the spring and early summer, flooded low-lying
areas that were not protected by dikes, and then receded. Usually this was more
of an inconvenience than a disaster. In April 1936, for example, as
construction got underway at Grand Coulee Dam, wooden frames around the
excavation pits could not hold back the river, which rose 10 feet by April 21.
Water poured into the excavations on the east side of the dam, delaying the
exceptions, however, are notable and important. The flood of 1894 crested in
the Columbia on June 6 and 7, when the flow at The Dalles, Oregon, 191 miles
inland from the ocean, peaked at 1,240,000 cubic feet per second on June 6. The
annual average flow at The Dalles, where river data has been collected since
1879, is 191,400 cubic feet per second. Some older buildings in downtown
Portland have painted lines as much as five feet above the sidewalks to show
the level of the Willamette River in the flood of 1894, and those buildings
are — and were — hundreds of feet from the shore. At Vancouver, where the river
level was monitored but not the flow velocity, the Columbia reached its
all-time record high on June 7, 1894, 34.4 feet above sea level. The normal
river level at the Vancouver gauge, which is located at river mile 106.5, five
miles upstream from the confluence of the Columbia and Willamette, is 1.2 feet
above sea level.
major flooding was rare. It was the tremendous volume of annual runoff that
attracted federal river planners, not the need for flood control. The river had
great potential for hydropower if only the vast volume of water could
be contained behind dams — which also would provide flood control.
first thorough analysis of the power potential came in response to the 1925
Rivers and Harbors Act, in which Congress directed the U.S. Army Corps of
Engineers and the Federal Power Commission to determine how much it would cost
to conduct a survey of the nation’s rivers and recommend ways to improve them.
The following year, 1926, the agencies reported their cost estimates in House
Document 308, and in the 1927 Rivers and Harbors Act Congress ordered the
surveys. These river reports, and others like them that followed over the
years, have been called “308 Reports” ever since.
Corps’ 308 Report of 1932 declared that Columbia floods could be handled by the
construction of dikes at communities where damages might occur. The report
focused on building dams to provide navigation on the lower Columbia and
virtually ignored discussion of upriver water storage projects. Three years
later in the 1935 Rivers and Harbors Act, Congress authorized construction of
Bonneville and Grand Coulee dams. In fact, the dams already were under
construction as New Deal-authorized projects. Grand Coulee would provide water
storage, hydropower and flood control; Bonneville would provide hydropower and
1937 the Corps’ Ben Torpen issued a report entitled “Where Rolls the Columbia,”
which recommended construction of storage dams that would enable greater
hydropower development than would be justified based on the Columbia’s erratic
annual flows. At the time, the ratio of the Columbia’s highest annual flow — 1.24 million cubic feet per second at The Dalles during the flood of 1894
the river’s lowest recorded flow — 36,000 cubic feet per second at the same
location in 1937 — was 34 to 1. Torpen proposed the development of 125 million
acre-feet of storage but said only about 67 million acre-feet was feasible.
Coincidentally, that is about how much storage ultimately was developed. Like
others who had studied the Columbia before him, Torpen’s proposals did not
excite much interest; his superiors at the Corps remained focused on
navigation. In 1943, there was renewed interest in Columbia Basin water storage
for hydropower purposes when the War Production Board asked the Corps and the
Bonneville Power Administration how electricity production might be increased
quickly for the war effort. This led to Congressional authorization of Hungry
Horse Dam on the South Fork Flathead River in Montana in 1944, a dam that would
provide hydropower, water storage for downstream power generation and flood
control. After some delays the dam was completed in 1952.
upstream storage for flood control, however, remained a low priority. That
changed in 1948. That year a monster spring flood not only was a disaster in
terms of property damage and lost lives, but it also prompted attention in
Congress and led to the construction of new dams.
late May and early June of that year, the river went on a rampage. The flood of
1948 was basinwide, affecting communities as far upriver as from British
Columbia. At Grand Coulee Dam, 595 miles inland on the Columbia from the ocean,
the river flow peaked on June 12 at 633,000 cubic feet per second, more than
three times average. At the Vancouver river gauge, the Columbia crested on June
13-14 at 31 feet above sea level.
flood lasted 20 days. The worst damage occurred in Vanport, Oregon, where the
flood waters broke through a railroad dike on May 29. Vanport, on the south
shore of the 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. Thirty-two people died and seven were
reported missing and presumed dead. The community of 18,000 was destroyed.
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. President
Harry Truman inspected the area and then ordered federal agencies to coordinate
their development of the river. Flood control was a priority. The flood, Truman
said, “should reinforce our determination to build the dams and other structures
needed to control the nation’s river basins.”
Corps quickly revised an update of the 308 Report, called HD531, that had been
underway for several years and issued it in October. The report contained
proposals for many new upstream dams, including some, like John Day Dam, that
would provide both hydropower and flood control. The new projects would reduce
the Columbia’s erratic flow ratio to a manageable 4 to 1 or 5 to 1 and make
large hydropower dams more feasible.
1948 report described 20 million acre-feet of potential water storage in the
United States and Canadian portions of the Columbia Basin. This water could be
used to generate electricity, and it also would help control floods, according
to the report. At the same time, and in conjunction with the HD531 Report, the
International Joint Commission issued a report that showed Canada
was willing to build storage dams in that part of the Columbia River Basin in
return for electricity or cash.
would take more than 20 years for the two countries to agree on the details,
but this initial interest in flood control would lead to the
Columbia River Treaty and the construction of Mica, Keenleyside and Duncan dams in
Canada and Libby Dam in the United States for the purpose of controlling floods
and maximizing downstream power generation.
Today, flood control storage totals 37 million acre-feet (45.7 billion cubic
meters). This is only flood-control storage. The total of all active storage in
all Columbia River Basin reservoirs is 55.8 million acre-feet.
storage includes 16.5 million acre-feet (20.4 billion cubic meters) in the
United States at the Grand Coulee, Albeni Falls (Lake Pend Oreille), Libby,
Hungry Horse and Dworshak dams, and 20.5 million acre-feet (25.3 billion cubic
meters) at the Columbia River Treaty dams in British Columbia. Flood control
also provided by major levee systems, which have been constructed along the
lower Kootenai River in the United States and Canada, the upper Flathead River
below Hungry Horse Dam, the Pend Oreille River below Albeni Falls Dam, the
lower Clearwater and Snake rivers near Lewiston, Idaho, and Clarkston,
Washington, the Columbia River in the Tri-Cities area, and at more than 20
locations in the lower Willamette and Columbia Rivers from the Portland area to