RESTORATION OF PHYSICAL PROCESSES AT THE RIPARIAN-ESTUARINE TRANSITION, NORTH DELTA, CA

The North Delta management area, CA includes lowland floodplains formed at the Mokelumne River, Dry Creek, Cosumnes River confluence and former fresh water-tidal marshes and slough channels in the Sacramento-San Joaquin River Delta. Prior to European settlement, geomorphic processes in the lowland river system were dominated by episodic avulsion, erosion, and sedimentation that occurred during floods over a wide range of magnitudes. These dynamic processes created habitat heterogeneity that supported a highly diverse multiple channel riparian system. Both tidal and fluvial processes operated further downstream in estuarine areas. Anthropogenic modifications in the past two centuries altered processes, morphology, and the sediment budget in the North Delta riparian-estuarine transitional area. Mining activities, construction of levees and dams, channel and slough dredging and large woody debris removal accompanied the alteration of floodplains and marshplains to agriculture, and subsidence of portions of the North Delta islands. Currently, levees isolate floodplain and island tracts from flows constrained in channels, and subsidence of peat soils challenges restoration designs. Geomorphic analyses and hydraulic modeling of the area suggest that removing constraints e.g. levee breaching would promote physical processes and lead to a potential continuum of physical environments extending through the fluvial-tidal transition.