Flood of 1996
From Lane Co Oregon
Jim Lichatowich commented on the 1996 flood:
The flood is like El Niño. The things we've done cause natural events to become problems. The salmon coped with floods and El Niños for thousands of years, but they haven't coped with us. We've torn up the habitat for 150 years, and then we point to events that have been there for thousands of years, saying they're the culprit for salmon decline. If the rivers had been healthy and the stocks healthy, they could have absorbed the flood. In fact, the floods of 1996 were not hundred-year floods except in a few of the hardest-hit areas. The flood of record for the Willamette River was in December 1861, when the river had a peak flow of 500,000 cubic feet per second (CFS). The Willamette's peak flow in 1996 was 365,000 CFS, considerably less. In the last 135 years, the Willamette had four floods that were larger than the 1996 flood—in 1861, 1881, 1890, and 1964. Several others were almost as large as the 1996 flood. For the Willamette River, the February 1996 flood was closer to a thirty-year flood than a hundred year flood.
On the McKenzie River, the 1996 flood was the size of a typical five-year flood before the dams were built in the 1960s. The Tualatin River near Portland was rated as having a ten-year flood. Where the cells of heaviest rain parked over watersheds, a few rivers really did have hundred-year floods. The Nehalem and Wilson Rivers in northwest Oregon; the Grande Ronde, Umatilla, Metolius, and Deschutes Rivers in eastern Oregon; and the Sandy and Clackamas Rivers east of Portland were all rated as having true hundred-year floods. The long intervals between floods make it difficult to learn from the events. People didn't know they were living on floodplains because the last flood was outside their experience. County zoning officials didn't know they were permitting construction on floodplains because most had started their careers after the 1964 flood. In many cases, home builders and officials thought that the new dams and levees completed since 1964 protected them. I heard about the 1964 flood because I lived in a rural area and also because I was interested in rivers. The Pacific Northwest's population was mostly urban, and city dwellers didn't hear much about the history of their landscape. In 1990, with almost 3 million people, Oregon's population was over 70 percent urban. Washington's population was more than 76 percent urban, out of almost 5 million people. Even lightly populated Idaho, with just over 1 million people, was over 57 percent urban. Thirty-two years is about the span of an average professional career, so only a few hydrologists and fish biologists near retirement age remembered the 1964 flood as a professional experience. Some middle-aged professionals recalled the event from living through it as kids. How did the 1964 flood affect rivers and fish? How long did biological recovery take? No one knew. We had lost our opportunity to learn from the past, but there were lessons to be learned from the 1996 floods. The floods of 1996 had opposite effects on healthy and unhealthy rivers. The McKenzie River, a fairly healthy river, acquired hundreds of new driftwood logs and held on to most of them. The logjams in the delta area grew larger and more complex. Gravel bars were scrubbed clean and renewed. Landslides added new boulders and wood to streams, and the currents sculpted more complex channels. Some homes were damaged along the lower McKenzie River, roads were ruined, and sediment loads were high in the river for a couple of days. People suffered some losses, but the river digested the flood well.
