The benefits and limitations of hydraulic modeling for ordinary high water mark delineation

Abstract : This document explores the use of hydraulic modeling for ordinary high water mark (OHWM) delineation as performed for the purposes of Clean Water Act implementation and other applications. OHWM delineation in streams and rivers is primarily based on field indicators, which can be challenging to interpret in these dynamic systems. Computational hydraulic modeling simulates the water surface elevation and width for a given discharge. This modeling can be helpful in OHWM delineations but can be misleading if the model assumptions are not met, the model inputs are not carefully chosen, or the error estimates of the model are unclear. This document demonstrates how hydraulic modeling can assist with OHWM de-lineation in rivers and streams and how modeling may be misused or misleading. Two separate companion documents focus on (a) flow frequency analysis and hydrologic modeling and (b) the combined use of hydraulic modeling and flow frequency analysis in OHWM delineation.