Lateral channel migration and bane erosion along the Marys River, Benton County, Oregon

The Marys River flows east from the Coast Range and across the Willamette V alley Quaternary sediments to Corvallis, where it enters the Willamette Riv er. Five sets of historic air photos, from 1936-1994, were used to map chan ges in channel location and riparian vegetation. Lateral channel migration has been dramatic in some parts of the river where it crosses the Willamett e Valley. Impressive lateral migration has taken place at the valley's west ern edge, where the bedrock changes from basalts in the Coast Range to unco nsolidated Willamette Valley sediments. Bank erosion accelerated the most w here riparian vegetation was removed, although banks also eroded where vege tation is present. Evidence suggests that a sediment wave is moving downstr eam. The headwaters of the Marys River watershed were logged during the fir st half of the 20(th) century, which probably introduced more sediment than could be transported. This sediment wave is now traveling through the lowe r watershed, causing gravel bar deposition and accompanying bank erosion. E ven so, the channel has stayed within a well-defined meander belt. Although the river flows through areas that are becoming more urbanized, few buildi ngs are within the meander belt. The meander belt appears to delineate a zo ne that should be protected from further development. In this way, concerns about bank erosion and property losses would be reduced.