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

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Bolsa Chica Lowlands Restoration Monitoring2007 Annual Reportchannel during Winter 2005/2006, providing approximately 102,500 m 3 (133,962 y 3 ) of beachnourishment (50:50 north and south) to the shoreline adjacent to the channel in Summer 2006 andestablishing tidal exchange at the entrance channel in August 2006.As indicated previously, the beaches along the Bolsa Chica study area has regularly benefited from thedowndrift dispersal of the Surfside-Sunset nourishment material. A comprehensive account of thecoastal changes in the area during the 34-year period between 1963 and 1997 can be found in theCCSTWS-OC (USACE, 2002).Profile ChangesLong-Term Profile Changes (1963 to 2007): The above-water beach profiles obtained in 2007 areeach near or seaward of the upper bound of the historical profile envelope at six of the seven BolsaChica area transects. The exception was Transect 378+29, located at Huntington Cliffs. Thesefindings are consistent with the long-term trend of beach width and sediment volume gainsidentified in the CCSTWS-OC for the Bolsa Chica study area. Of the five historical transects, theaccretion trend was absent only at Transect 378+29.Bolsa Chica Monitoring Period Changes (2005 to 2007): During the two-year Bolsa ChicaMonitoring Period, significant above-water profile accretion occurred at the three transects locatednorth of the entrance channel (249+30, 311+22, and 318+30). Similar gains also occurred at thesouthernmost transect (423+89). At Transect 330+30, modest above-water profile gains wereevident seaward of the berm near the back beach. In contrast, the above-water beach at Transects350+71 and 378+29 was characterized by modest erosion or stability. The volume gains at the twotransects located adjacent to the entrance channel (318+30 and 333+30) are likely attributable tothe beach nourishment placed in Summer 2006. The onshore migration of the material placed inthe ebb bar also may have contributed to the gains in the region.Offshore Ebb Bar: Approximately 929,326 m 3 of sand was placed in an ebb bar located offshore ofthe Bolsa Chica entrance channel between November 2005 and May 2006. This bar is evident inthe 2007 profiles at Transects 311+22, 318+30 and 333+30. The profiles obtained during 2007indicate that the ebb bar was relatively stable during this period. The most significant changeswere isolated to depths above 4 m.Beach Width Changes2007 Beach Widths: Figure 2-11 shows the beach widths in the Bolsa Chica study area at the timeof the May 2007 and October 2007 surveys. The figure also includes the range of Fall and Springbeach widths for all available data. At the time of the May 2007 survey, beach widths ranged from28 m at Transect 378+29 to 107 m at Transect 423+89. The greatest beach width at the time of theOctober 2007 survey was 113 m (Transect 423+89), while the narrowest beach width was 41 m(Transect 378+29). Both the May and October 2007 beach widths were near or above theirrespective historical beach width envelopes. This finding is consistent with the long-term trend ofshoreline advance identified in the CCSTWS-OC.Long-Term Shoreline Changes (1963 to 2007): The time series plots in Appendix 2-C indicate atrend of long-term shoreline advance at six of the seven Bolsa Chica area transects during the 44-Merkel & Associates, Inc. 81
Bolsa Chica Lowlands Restoration Monitoring2007 Annual Reportyear period between 1963 and 2007. The exception was Transect 378+29, where beach widthswere relatively stable during this period with no apparent trend.Figure 2-11. May 2007 and October 2007 Beach Widths.Figure 2-12 shows the net long-term beach width changes in the Bolsa Chica study area between May1963 and May 2007. To avoid a seasonal bias, the comparison utilizes the May 2007 survey ratherthan the more recent October 2007 survey. Shoreline advance predominated, with gains ranging from16 m at Transect 350+71 to 65 m at Transect 318+30. Shoreline retreat occurred at only one location,a loss of 6 m at Transect 378+29.Merkel & Associates, Inc. 82
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MutedPocket MarshSTATION 1wq1STATIO
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