Latest Pleistocene and Holocene (2-16Â ka) sedimentation in the Columbia River Estuary, Oregon, USA

The total volume of Holocene sediment, primarily bedload, which has accumulated in the lower Columbia River valley, is 73 km3. This compares to only 13-km3 accumulation during the last 5 ka. The tidal basin accumulation rate gradually increased from 0.6 million m3/yr to slightly over 18 million m3/yr between the depths of 112 m and 30 m (16 to 9 ka). Above the 30 m depth (corresponding to 8.2 ka), the rate of basin volume fill dramatically decreased to just over 4 million m3/yr. Such a large decrease in sediment accumulation rate suggests that after 9 ka sediments were bypassing the nearly full tidal basin to the beaches and inner shelf. The rates of bedload bypassing the lower Columbia River valley, substantially greater than 2.4 million m3/yr, supported the shoreface progradation in the littoral cell during the late Holocene.