UT NP ARCH100 Bridges on Delicate Arch Road Hydraulics Report Signed

Bridges on Delicate Arch Road
Final Hydraulics Report

UT NP ARCH 100(2)

In partnership with:

National Park Service, Arches National Park
Grand County, UT

Federal Highway Administration
Central Federal Lands Highway Division

July 29, 2026

Signature Sheet

Report prepared by:

signed by LUIS GERARDO CALDERON

LUIS GERARDO CALDERON Digitally

Date: 2026.07.29 11:44:52 -06'00'

Luis Calderón, Lead Hydraulic Engineer

Report reviewed by:

Digitally signed by AMANDA ANN

AMANDA ANN

PETERS

Date: 2026.07.29 11:50:36 -06'00'

PETERS

Amanda Peters, Hydraulic Engineer
Report approved by:

signed by LUIS GERARDO CALDERON

LUIS GERARDO CALDERON Digitally

Date: 2026.07.29 11:52:07 -06'00'

Luis Calderón, Lead Hydraulic Engineer

Distribution
Electronic: N:\UT\arch100(2)\Hydraulics\9_Final-Report
Steven Davis, Project Management
Erin Jessee, Project Development, Design Team Leader
Jeff Felling, Project Development, Lead Designer
Carolyn Arroyo, Project Development, Lead Designer
Devin Dixon, Lead Geotechnical Engineer
Karl Eikermann, Supervisory Bridge Engineer
Brian Fauver, Environmental Protection Specialist
Ron Andresen, Materials Engineer
Kevin Vanzo, Construction Operations Engineer
Richard Vanderbeek, Land Surveyor (ROW)

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UT NP ARCH 100(2) – Final Hydraulics Report

Executive Summary
Hydrologic and hydraulic analyses were conducted for the UT NP ARCH 100(2), Bridges on Delicate Arch Road project located in Arches National Park, Grand County, UT. The project scope is to replace 3 existing culvert crossings on Salt Valley, Salt, and Winter Camp Wash with bridges that will improve flood capacity and sediment transport. The adopted hydraulic capacity design frequency is the 10-year flood. This was selected in agreement with Arches NP as a compromise between project impacts and maintenance of flow connectivity. Design peak flows were estimated using USGS regression equations and an NRCS rainfall-runoff model conducted in HEC-HMS. Adopted flows are based on the lower bound of the regression equations.
Proposed conditions two-dimensional hydraulic modeling was conducted using SRH-2D to estimate water surface elevations, depths, and flow velocities at the project sites. The proposed configuration at the sites are bridge structures with 1V:3H spill-through abutment slopes. Low chord elevations at the three sites will provide a minimum of two feet of freeboard above the 10-year design flood but in most cases will exceed this criterion. For the design storms evaluated, only the Salt Wash bridge experiences pressure