2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

Bolsa Chica Lowlands Restoration Monitoring
2008 Annual Report
develop a set of “synthetic” profiles for the survey years with data that were not coincident with the
CCSTWS-OC transect locations (typically the pre-1992 surveys). For the purposes of the Bolsa Chica
monitoring program, the same TIN model approach was used to “re-generate” the synthetic profiles
used in the CCSTWS-OC. This approach was not necessary for the data that were coincident with the
transect locations (1992-1997 and 2002).
The LIDAR data consists of densely spaced topographic points derived from an airborne survey.
These data encompass the entire shoreline of the Bolsa Chica study area, but do not extend below the
waterline. Beach profiles were created at each of the five historical transects and the two newly
established transects using a TIN model developed from the LIDAR results.
Synthetic profiles also were developed for the two newly established transects for March 2002 and
several of the pre-1992 CCSTWS-OC survey dates. Using the same TIN model approach described
above, synthetic profiles were created for each case when historical survey data bracketed the location
of the two newly established transects and at least one of the bracketing transects was not coincident
with a historical transect. Profiles were generated for the following eight survey years: May 1963,
July 1964, October 1966, April 1969, May 1973, April 1982, January 1983, and March 2002.
Historical Beach Width Measurements
U.S. Army Corps of Engineers personnel have acquired monthly beach width measurements along the
Orange County coast since 1977. This extensive data set was initiated by Robert Clancy. Since the
late 1980’s, Chuck Mesa of the Corps has continued the monthly data collection program.
The data set contains measurements from a consistent back beach position to the break-in-slope at the
beach berm. The location of the berm does not represent a vertically-referenced shoreline (such as the
MSL shoreline). However, the measurements do provide an indication of gross changes in beach
configuration. To differentiate these measurements from beach widths derived from profile data or
from the beach width measurements collected on behalf of the Bolsa Chica project, they will be
referred to hereafter as “Corps beach widths”.
Three of the measurement stations are located within or immediately adjacent to the Bolsa Chica study
area: 247+88, 308+88, and 424+44. These stations are not coincident with the transect locations used
for the CCSTWS-OC or the Bolsa Chica monitoring program. The beach width measurements at these
stations were retrieved from the U.S. Army Corps of Engineers (Mesa 2008b, 2009).
Methodology
Beach Profile Surveys
Beach profile data were obtained on two occasions in 2008: May 12 and October 28. The methods
employed were similar to those used on previous Orange County surveys. In consequence, the results
are directly comparable. The data acquisition and reduction methods are described below.
The wading and bathymetric portions of each survey were performed concurrently by two crews, as
illustrated in Figure 2-10. Data were acquired along each transect from the back beach to a depth of
approximately 14 m below NAVD88. Wave heights typically were less than 1 m during each of the
surveys.
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