Large-scale sand waves (dunes) occur over much of the Columbia River bottom from near the mouth at Astoria, Oregon, upstream to The Dalles (including Bonneville Reservoir), a distance of 280 kilometers. The waves range in height from less than a meter to 7 meters, but most are 2-2½ meters high. Common lengths are 40-60 meters. Virtually all waves are asymmetrical, with steep slopes facing downstream. The mean particle size of bottom sediment is in the range of fine to very coarse sand. The migration rate for a group of waves in Bonneville Reservoir was approximately 0.6 meter/day during a 2-week period of high water in mid-June, 1966 (average current speed, 0.7 meter/second), decreasing to 0.3 meter/day in the following month at lower stages of the river.

Sand waves are not uniformly developed throughout the river. Within Bonneville Reservoir the location of waves apparently is determined by the availability of sand-size sediment and the river's flow characteristics. Just below Bonneville, the patchy wave distribution may be caused by coarse sediment (gravel) and (or) high current speed; near the mouth, waves apparently are not well developed because of variable directions of current flow during the tidal cycle. Water depth has no consistent effect on the location or size of the waves.

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