Reflecting on the Sandy River's Record 1964 Flood

The “Christmas Flood” of 1964 stands in the history books as the flood of record for the Sandy River. Many rivers throughout Oregon reached similar record-breaking levels, though the Sandy River corridor was one of the hardest-hit regions throughout the state.

What we now know as an “atmospheric river” storm event dumped over 15 inches of rain on top of deep early December snow. Raging high water, logs and other debris drove the river through broad channel migration, redirecting itself through soft volcanic deposits and neighborhoods.

A US Army Corps of Engineers report afterward counted over 150 homes destroyed. Bridges, roads and other infrastructure washed away by the storm stranded hundreds of families. The Brightwood area saw 40 homes completely wiped out, along with mudslides, and stream bank erosion that redrew the landscape in the upper Sandy. Bridges washed out in Rhododendron and residents in ZigZag were stranded until local community members worked together to rescue their neighbors. That year’s flood and its aftermath also had a profound impact on the river and its wild salmon habitat.

Seeking to prevent damage from floods after 1964, the U.S. Army Corps of Engineers built large embankments along straightened main channels in the upper river to try to contain the glacially driven Sandy, in the process mowing down vegetation in riparian zones. The simplification and channelization following the flood cut off key floodplain and off-channel habitats, which juvenile salmon and steelhead rely on as places to rest and feed during their migration.

The newly built levees were designed to protect local residents from flood impacts, but the Sandy River’s migrating channel altered the engineered landscape even within the next few years. Aerial photos depicting the Sandy River near Timberline Rim show drastic changes over the 5-year period between 1967 and 1972 (below). Also visible is the rapid development that occurred along the banks of the Sandy River after the 1964 historic floods.

The 1964 floods were considered a “100 year” event, meaning that there is a 1% probability of the river reaching that level in any given year. While it’s only been 50 years since this impactful flood, residents in the Sandy River corridor should be aware that large floods can occur any winter, and climate models and data predict more frequent and intense storms in the future. Since the most recent flood event in 2011, the Clackamas County emergency management department has installed early-warning flood gauges in the upper basin to act as a signal to local residents that flood waters will be coming. Those gauge readings should be online soon, but will only read data when the river is near or at flood stage.

Restorative Flood Response

The Sandy River Basin Watershed Council has been engaging local community members through our Restorative Flood Response program since the 2011 flood. We have increased the dialogue around the reality that a 1964-level flood can happen again at any time, and we seek to improve salmon spawning habitat while addressing flood risk on the mainstem Sandy River and its tributaries.

As we expand our understanding of channel migration, river geomorphology and hydrology, the Council is developing a Restorative Flood Response Handbook for local residents in the upper watershed. Additionally, Clackamas County is studying erosion risk on a 10-mile reach of the upper Sandy River, with a report to be published in early 2015. The Council is planning to restore a demonstration area for floodplain reconnection that benefits habitat and addresses potential flood risk in the summer of 2015.

For more background on the Christmas Floods of 1964 in the Sandy and elsewhere, take a look at these resources:

(Aerial photos Courtesy of Clackamas County, other photos from the Estate of Joie Smith)

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