As part of a multiagency collaboration, the USGS commemorated the 50th anniversary of the 1964 Flood. Information about the event, stories, timelines, and other tools were provided through the Silver Jackets organization.
THE "CHRISTMAS" FLOOD OF 1964
December 1964 and January 1965 saw extreme flooding across much of the Pacific Northwest. The flooding was so severe in some rivers that the streamflow observed at the time still stands as the highest ever recorded in those areas. Along with record-breaking streamflow, the storms resulted in the transport of an extraordinary amount of sediment and caused extensive property damage across the region. Landslides, washouts, and streambed and bank erosion contributed to the sedimentation and further compounded the floodwater damage. According to reports at the time, 47 people died and more than $514 million ($3.9 billion in today’s dollars) worth of damage occurred that winter. Yet, despite the immense flooding, storage in reservoirs and operation of flood-control facilities were effective in preventing far greater damage in many areas, particularly in the Willamette River Basin in Oregon.
The severe flooding in 1964 did not relate to a single storm, but rather a series of storms between December 19, 1964, and January 31, 1965. The first peak flow event December 19 to 23 was the largest and most expansive during this period. The highest peak for many of the streams, including the Willamette River, occurred December 23 when rain fell on high elevation snowpack, melting the snow and adding the runoff to already high stream conditions. Subsequent storms between January 21 and January 31 flooded streams in northeastern Oregon and southeastern Washington, as well as returned streams along the coast and the Willamette River valley to conditions like those seen in December.
FREQUENTLY ASKED QUESTIONS
Below are FAQ associated with this project.
We had a "100-year flood" two years in a row. How can that be?
The term "100-year flood" is used to describe the recurrence interval of floods. The 100-year recurrence interval means that a flood of that magnitude has a one percent chance of occurring in any given year. In other words, the chances that a river will flow as high as the 100-year flood stage this year is 1 in 100. Statistically, each year begins with the same 1-percent chance that a 100-year...
What are the two types of floods?
There are two basic types of floods: flash floods and the more widespread river floods. Flash floods generally cause greater loss of life and river floods generally cause greater loss of property. A flash flood occurs when runoff from excessive rainfall causes a rapid rise in the water height (stage) of a stream or normally-dry channel. Flash floods are more common in areas with a dry climate and...
Where can I find flood maps?
FEMA is the official public source for flood maps for insurance purposes: FEMA’s Flood Map Service Center FEMA’s National Flood Hazard Layer NOAA is responsible for producing flood forecast maps that combine precipitation data with USGS streamflow data: National Weather Service - Advanced Hydrologic Prediction Service River Forecasts Long-Range River Flood Risk Coastal Inundation Dashboard: Real...
Why do the values for the 100-year flood seem to change with every flood?
The amount of water corresponding to a 100-year flood, a 500-year flood, or a 1,000-year flood is known as a "flood quantile". For instance, on a given river, the flood quantile corresponding to the 50-year flood might be 10,000 cubic feet per second (cfs) and the flood quantile corresponding to the 100-year flood might be 15,000 cfs. The estimates of the flood quantiles are calculated using...
- Overview
As part of a multiagency collaboration, the USGS commemorated the 50th anniversary of the 1964 Flood. Information about the event, stories, timelines, and other tools were provided through the Silver Jackets organization.
THE "CHRISTMAS" FLOOD OF 1964
December 1964 and January 1965 saw extreme flooding across much of the Pacific Northwest. The flooding was so severe in some rivers that the streamflow observed at the time still stands as the highest ever recorded in those areas. Along with record-breaking streamflow, the storms resulted in the transport of an extraordinary amount of sediment and caused extensive property damage across the region. Landslides, washouts, and streambed and bank erosion contributed to the sedimentation and further compounded the floodwater damage. According to reports at the time, 47 people died and more than $514 million ($3.9 billion in today’s dollars) worth of damage occurred that winter. Yet, despite the immense flooding, storage in reservoirs and operation of flood-control facilities were effective in preventing far greater damage in many areas, particularly in the Willamette River Basin in Oregon.
The severe flooding in 1964 did not relate to a single storm, but rather a series of storms between December 19, 1964, and January 31, 1965. The first peak flow event December 19 to 23 was the largest and most expansive during this period. The highest peak for many of the streams, including the Willamette River, occurred December 23 when rain fell on high elevation snowpack, melting the snow and adding the runoff to already high stream conditions. Subsequent storms between January 21 and January 31 flooded streams in northeastern Oregon and southeastern Washington, as well as returned streams along the coast and the Willamette River valley to conditions like those seen in December.
FREQUENTLY ASKED QUESTIONS
- Publications
- FAQ
Below are FAQ associated with this project.
We had a "100-year flood" two years in a row. How can that be?
The term "100-year flood" is used to describe the recurrence interval of floods. The 100-year recurrence interval means that a flood of that magnitude has a one percent chance of occurring in any given year. In other words, the chances that a river will flow as high as the 100-year flood stage this year is 1 in 100. Statistically, each year begins with the same 1-percent chance that a 100-year...
What are the two types of floods?
There are two basic types of floods: flash floods and the more widespread river floods. Flash floods generally cause greater loss of life and river floods generally cause greater loss of property. A flash flood occurs when runoff from excessive rainfall causes a rapid rise in the water height (stage) of a stream or normally-dry channel. Flash floods are more common in areas with a dry climate and...
Where can I find flood maps?
FEMA is the official public source for flood maps for insurance purposes: FEMA’s Flood Map Service Center FEMA’s National Flood Hazard Layer NOAA is responsible for producing flood forecast maps that combine precipitation data with USGS streamflow data: National Weather Service - Advanced Hydrologic Prediction Service River Forecasts Long-Range River Flood Risk Coastal Inundation Dashboard: Real...
Why do the values for the 100-year flood seem to change with every flood?
The amount of water corresponding to a 100-year flood, a 500-year flood, or a 1,000-year flood is known as a "flood quantile". For instance, on a given river, the flood quantile corresponding to the 50-year flood might be 10,000 cubic feet per second (cfs) and the flood quantile corresponding to the 100-year flood might be 15,000 cfs. The estimates of the flood quantiles are calculated using...
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