Ayres Knowledge Center Scour Evaluation: Bridges with Unknown Foundations | Page 14

INTRODUCTION / MODEL SETUP
The hydraulic analysis uses an unsteady state simulation of the 100-year and 500-year event
conditions using HEC-RAS (v. 4.1.0). The bridge was modeled as part of a larger model that
incorporates multiple bridges in the intracoastal waterway/ Halifax River. A model based on four
cross-section survey data at the Bridge 794004 (Ayres, 2011), the NOAA Technical
Memorandum NESDIS NGDC-19 (Digital Elevation Model (DEM) of Daytona Beach, Florida,
March 2009), and Volusia County 1-ft Lidar data was developed to predict the hydraulic
conditions at the various bridge crossings for the storm event discharges. All elevations are
NAVD-88.
Bridge plans from 1957 were available for this bridge, and provided details of the bridge deck
thickness, pile bent configuration and size, pile bent pile cap size and details of the bascule
piers. The bridge plans were supplemented with data taken from the roadway centerline
survey.
The model was run for both the 100-year and 500-year event storm surges at the Ponce de
Leon Inlet. The computed 100-year event water surface elevations were compared to the
Volusia County Flood Insurance Study (FIS) Stillwater elevations for verification (Attachment D).
CROSS SECTIONS
A survey was conducted and four cross sections were provided at the upstream channel,
upstream bridge fascia, downstream bridge fascia, downstream channel, road centerline and
other pertinent bridge data. The survey is tied to a brass cap set in southeast abutment wall
(N=1777824.824, E=651460.511, Z= 9.042) and a brass cap set in the northwest abutment
(N=1776978.177, E=649505.681, Z=7.423). The survey data was supplemented by the NOAA
Daytona DEM and 1-ft Lidar available from Volusia County to extend the surveyed cross
sections and to add sections beyond the survey limits.
Below are selected results from HEC-RAS model related to Bridge 794004 that were used for
scour related calculations.
!"#$"% #%&&&&&&&&&&&&&&&&&&&'()*+
Supplementary Report
,-./&#!&01&2#
3%4 #225%2&&&&&&&&&&&&&&&&&&67(89:&);&<=2
Page SR-14
2