Physical Model of Current-Induced Scour
at Ventura Harbor
Steven A. Hughes1 and Bradd R. Schwichtenberg2
Abstract:
This paper describes a 1:25-scale movable-bed physical
model study of scour resulting from longshore current passing through a
narrow gap on the leeside of the detached breakwater at Ventura Harbor,
California, USA. The physical model was calibrated by adjusting the total
scour hole measured at Ventura Harbor. The calibrated model was then
used to predict future scour potential and to optimize the design for re-
medial toe protection intended to prevent leeside armor layer damage on
the detached breakwater. In addition, the model study identified and e-
liminated several construction problems that could have caused significant
unforeseen expenditures.
Introduction
Since its original construction in 1963, the entrance to Ventura Harbor has undergone
a series of engineering modifications in an effort to decrease deposition of littoral
sediments in the navigation channel. Construction of a detached breakwater with
a large sand trap in the lee eased the shoaling problem somewhat, but some sand
still escaped the sand trap and entered the navigation channel. Further improvements
alleviated the shoaling problem; however, a flow constriction was created that resulted
in severe scour during a fierce storm. The scour undermined the leeside toe of the
detached breakwater and caused the armor layer to slump.
This paper describes a movable-bed model investigation that established the scour
mechanism, determined that future scouring of the breakwater toe was inevitable, and
developed effective toe protection that resulted in significant cost savings. The model
was calibrated by adjusting the flow condition to reproduce the original scour hole
measured at Ventura Harbor. Simple analytical tools provide reasonable estimates of
1
Research Hydraulic Engineer, US Army Engineer Research and Development Center, Coastal and
Hydraulics Laboratory, 3909 Halls Ferry Road, Vicksburg, Mississippi 39180-6199 USA.
2
Hydraulic Engineer, US Army Engineer District, Jacksonville, 400 West Bay Street, Jacksonville,
Florida 32256 USA.
1
Hughes/Schwichtenberg