2007 Annual Monitoring Report (pdf 16MB) - Bolsa Chica Lowlands ...

Bolsa Chica Lowlands Restoration Monitoring2007 Annual ReportSynthetic profiles were also developed for the two newly established transects for March 2002 andseveral of the pre-1992 CCSTWS-OC survey dates. Using the same TIN model approach describedabove, synthetic profiles were created for each case when historical survey data bracketed the locationof the two newly established transects and at least one of the bracketing transects was not coincidentwith 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 MeasurementsUSACE personnel have acquired monthly beach width measurements along the Orange County coastsince 1977. Mr. Robert Clancy initiated this extensive data set. Since the late 1980’s, Mr. ChuckMesa 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 thebeach berm. The location of the berm does not represent a vertically-referenced shoreline (such as theMSL shoreline). The measurements, however, do provide an indication of gross changes in beachconfiguration. To differentiate these measurements from beach widths derived from profile data orfrom the beach width measurements colleted on behalf of the Bolsa Chica project, they will be referredto hereafter as “Corps beach widths”.Three of the measurement stations are located within or immediately adjacent to the Bolsa Chica Studyarea: 247+88, 308+88, and 424+44. These stations are not coincident with the transect locations usedfor the CCSTWS-OC or the Bolsa Chica monitoring program. The beach width measurements at thesestations were retrieved from the USACE (Mesa, 2008b).MethodologyBeach Profile SurveysBeach profile data were obtained on three occasions in 2007: January 16, May 8 and 11, and October16. The methods employed were similar to those used on previous Orange County surveys. Inconsequence, the results are directly comparable. The data acquisition and reduction methods aredescribed below.Two crews performed the wading and bathymetric portions of each survey concurrently, as illustratedin Figure 2-10. Data were acquired along each transect from the back beach to a depth ofapproximately 14 m below NAVD88. Wave heights typically were less than 1 m during each of thesurveys.The beach and surf zone were surveyed using a total station and a survey rodman. The total stationwas used to determine the position and elevation of the beach at each location occupied by the rodman.Each transect was surveyed from the back beach seaward through the surf zone until the survey rod nolonger protruded above the water surface when held erect. This location, typically in a water depth of3.0 to 3.5 m below NAVD88, provided substantial overlap with the landward portion of thebathymetric survey.Bathymetric data were collected with a digital acoustic echo sounder operated from a shallow-draftinflatable survey vessel. A dynamic motion sensor, which provides real-time corrections to the echosounder for wave-induced vessel heave, was also utilized. A GPS receiver was used to determine theposition of each sounding. To improve the accuracy of each position, differential correctionsMerkel & Associates, Inc. 76