Restoration of Dynamic Floodplain Topography and Riparian Vegetation Establishment through Engineered Levee Breaching

Engineered levee breaches on the lower Cosumnes River, Central California, create hydrologic and geomorphic conditions necessary to construct dynamic sand splay complexes on the floodplain. Sand splay complexes are composed of a network of main and secondary distributary channels that transport sediment during floods. The main channel is bounded by lateral levees that flank the breach opening. The levees are separated into depositional lobes by incision of secondary distributary channels. The dynamic topography governs distribution of dense, fast-growing cottonwood (Populus fremontii) and willow (Salix spp.) stands. In turn, establishment and growth of these plants influences erosional resistance and roughness, promoting local sedimentation and scour. Cottonwood and willow establishment is associated with late spring flooding and the occurrence of abundant bare ground.