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

Bolsa Chica Lowlands Restoration Monitoring2007 Annual ReportBolsa Chica State BeachCityof Huntington Beach80249+30311+22318+30333+30350+71378+29423+8970Beach Width Change (m)6050403020100-10-200 1 2 3 4 5 6Alongshore Distance (km)Figure 2-13. Bolsa Chica Monitoring Period Shoreline Changes, October 2005 to October 2007.Sediment Volume ChangesLong-Term Subaerial Volume Changes (1963 to 2007): The long-term subaerial volume trends(Appendix 2-D) were similar to the long-term shoreline changes. Volume gains occurred at six ofthe seven Bolsa Chica area transects during the 44-year period between 1963 and 2007. Theexception was Transect 378+29, where subaerial volumes were relatively stable during this periodwith no apparent trend. Figure 2-14, which shows the net long-term subaerial volume changesbetween May 1963 and May 2007, bears a striking resemblance to Figure 2-11 (showing shorelinechanges for the same period).Bolsa Chica Monitoring Period Subaerial Volume Changes (2005 to 2007): Subaerial volumechanges during the two-year Bolsa Chica Monitoring Period are shown in Figure 2-15. Thevolume changes north of the channel were very similar to the beach width changes. In contrast tothe predominance of shoreline retreat south of the entrance channel, subaerial volume loss occurredat only one transect in this region. This apparent discrepancy at Transect 333+30 (immediatelysouth of the entrance channel) can be explained by the erosion of the beach between the waterlineand the berm (resulting in shoreline retreat) accompanied by stability from the berm to the backbeach (preserving the volume of sand nourishment placed in this area). The volume gains atMerkel & Associates, Inc. 84