Sedimentation in the lower Yuba and Feather Rivers

摘要: Hydraulic gold-mining tailings produced in the late 19th century in the Sierra Nevada foothills of California caused severe channel aggradation in the lower Feather and Yuba Rivers. Topographic and planimetric data from historical accounts, maps, topographic surveys, vertical sections, aerial photographs, and LiDAR data reveal contrasting styles of channel change and floodplain evolution between these two rivers. For example, levee cross-channel spacings up to 4 km along the lower Yuba River are in contrast to spacings less than 2 km on the larger Feather River. More than a quarter million cubic meters of hydraulic mining sediment were stored along the lower Yuba River and the wide levee spacing was intentionally maintained during design of the flood-control system to minimize delivery of sediment to navigable waters downstream. Consequently, the lower Yuba floodplain has a multi-thread highwater channel system with braiding indices> 12 in some reaches. Some of the larger of these channels remain clearly visible on aerial photographs and LiDAR imagery in spite of intensive agricultural leveling. Narrow levee spacings on the Feather River were designed to encourage transport of mining sediment downstream and keep the channel clear for navigation. Levee spacings on the lower Feather River reached a minimum near the turn of the 20th century when floodplain widths were reduced at several constricted reaches to less than 250 m. Historical data indicate that the general channel location of the lower Yuba River had stabilized by the end of the 19th century while substantial channel avulsions began later and continued into the …