SUNSET BEACH BRIDGE CURRENT STUDY, SUNSET BEACH, NC


North Carolina Department of Transportation (NCDOT) 
intends to replace the existing bridge across the 
intracoastal waterway connecting Sunset Beach to the 
mainland. A national coastal engineering firm was 
contracted by NCDOT to perform a design analysis for the 
new bridge that includes detailed analysis of scour around 
bridge pilings and foundations. This analysis will be based 
on the numerical models being developed for the site. To 
calibrate the numerical models, simultaneous current 
measurements over at least one tidal cycle in the 
numerous creeks and inlets surrounding the bridge location 
were required. Evans-Hamilton, Inc. (EHI), was contracted 
to perform a current survey along 30 range lines in the 
project area over a 2-day period. 

ADCP on Retractable Mounting Bracket. 
SCOPE AND APPROACH 

To perform the current survey, EHI outfitted two boats with 
1,200-kHz ADCPs on retractable mounts. Differential 
Global Positioning System (DGPS) was integrated into the 
ADCPs and was used to provide navigational information. 
Retractable mounts were required so that the ADCPs could 
be pulled out of the water and the boats could rapidly 
transit from one transect to the next, thereby increasing the 
number of transects that could be completed in a day. 

Over a 2-day period, more than 250 transect lines were 
run, capturing approximately two complete tidal cycles. 

The data were processed using custom software to provide 
both visual representations of the data and digital data that 
could be fed directly into the numerical models. Data 
output formats were customized to be consistent with the 
client's requirements. 

RESULTS 

Results of the study are still being compiled, but preliminary 
data have been useful in identifying the tidal nodal point for 
the system that is near the bridge. In addition, discharge 
data measured along the transects have been used to 
develop the preliminary model configuration and identify 
which channels are the prime contributors to the flow in the 
region around the proposed bridge location. The project is 
on schedule and within budget. 

Velocity Vectors Showing Current Magnitude and Direction