Willamette River Adjustments to New Spur Dikes

Severe bank erosion has caused recent local losses of up to 30 ft (9 m) per year of prime agricultural land along a half-mile (800 m) reach of the Willamette River, Oregon. The U. S. Army Corps of Engineers designed eight rock groins (spur dikes) to protect part of the eroding bank. These were built in summer 1983. The authors provided hydraulic data for Corps of Engineers design and physical modeling of the river reach. The authors developed a more-qualitative physical model to predict flow patterns and scour near the dikes and then monitored the flow and scour patterns at the prototype dikes after construction was completed. Some of the major local changes that took place as the river adjusted to the spur dikes during their first year in place are described.