Valley Regions

Introduction

When viewed in cross-section, a river corridor has several discrete elevational zones that are formed by different processes and accomodate different amounts of flow. Each elevational zone can be given a name, a qualitiative description, and a quantitative characterization. Taken together, these zones are termed "valley regions" when focusing on their form or "inundation zones" when focusing on the flows they accomodate. The purpose of this page is to present the valley regions for the lower Yuba River.

2006-2008 LYR Valley Regions

Given the LYR topogrpahic map produced using surveys that were primarily done in 2006 and 2008, 2D hydrodynamic models were run to determine the inundated area for each of several key flows. In addition, the outermost alluvial valley extent was mapped by an expert geomorphologist, with the constrant to remain inside man-made levees and training berms, not to span the full width of the potential alluvial valley if such structures were not present.

List of Valley Regions:

1. In-channel bed (aka riverbed) region: baseflow wetted area when a discharge of 880 cfs is released out of Englebright Dam and 530 cfs is released below Daguerre point Dam.
2. In-channel banks region: the region containing the bankfull wetted area, excluding the in-channel bed region. This includes active alluvial bars. A bankfull discharge of 5,000 cfs applied to the 2D model was used to map this area, and it also involved running the model with no vegetation present to map the area controlled exclusively by topography.
3. Floodway region: floodplain adjoining the bankfull channel and bounded on the outer fringe by a rise either to a terrace level or onto the hillside. A flow of 21,100 cfs applied to the 2D model was used to map this area, and it also involved running the model with no vegetation present to map the area controlled exclusively by topography.
4. Valley/terrace region: distal alluvial landforms isolated from the floodplain by a topographic riser.

2006-2008 Valley Region maps

These maps are available upon request.

Bibliography

• Wyrick, J. R. and Pasternack, G. B. 2012. Landforms of the Lower Yuba River. Prepared for the Yuba Accord River Management Team. University of California at Davis, Davis, CA, 91pp.