Evaluation of Paleoflood Peak Discharge Estimates in Hydrologic Hazard Studies

The findings of this study are a compilation of two different research projects. The initial project considered the differences in peak discharge estimates made using a single cross-section slope-conveyance calculation with the Manning equation (Method 1) to discharge estimates made using a more sophisticated one-dimensional hydraulic model (i.e., HEC-RAS; Method 2). Initial results were documented in a draft report with the same title as this report, but dated December 2007. The findings of that report have been updated and are included in their entirety in this research project, which supersedes the findings of the draft report.

The second study included a similar evaluation as the previously mentioned study, but in this case comparing one-dimensional model results (Method 2) to two-dimensional hydraulic model (SRH2D) results (Method 3). At the time of the first study, the two-dimensional hydraulic model SRH2D was not fully developed, and the detailed topographic data needed as model input were not readily available. Over several years the development of SRH2D improved to the point that it can easily be applied to a paleoflood study as long as the topographic data are sufficiently detailed (Lai, 2009). After using SRH2D to estimate peak discharge on several projects (Los Banos IE, Klinger and Bauer, 2004; Whiskeytown CAS, Klinger and Bauer, 2009; Anderson Ranch IE, Klinger and Bauer, 2010), enough data were available with which to compare one and two-dimensional model results.