Yuba Goldfields Fluvial Geomorphic Assessment
cbec performed a geomorphic assessment of the lower Yuba River adjacent to the Yuba Goldfields.
The focus of the effort was to assess the historic rates and predict future rates of lateral migration of the river and subsequent erosion of the training walls. The training walls were built from unconsolidated gravel and cobble to confine the river to an alignment to the north of its historic course. Although they are not levees, the training walls provide some flood relief to the areas south of the river. However in some locations the walls have eroded substantially, and now could be over-topped by a 100-yr flood.
cbec’s analysis included: field measurements (topographic surveys, grain size characterization), literature review, historical aerial photo analysis, 2D hydraulic modeling and statistical regression modeling in order to predict future bank retreat. For specific locations and time periods, rates of training wall retreat (as determined from aerial analysis) were determined. Total work performed during each period was determined using the historical flow record and a 2D hydraulic model. The bank retreat and cumulative work values were used to develop a statistical regression that allowed the estimation of the amount of bank retreat that would occur during an individual flood (100-yr storm) or historical period (10 years of actual flow).