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

Bolsa Chica Lowlands Restoration Monitoring2007 Annual ReportPlots of tidal elevations within the FTB and LAOH over this time period between December 21, 2006and January 31, 2008 are presented on a monthly basis for the entire data set in Appendix 2-A. Figure2-7 shows a tidal comparison of February 2007, seven months after the inlet was connected to theocean in August 2006.2.502.001.501.000.500.00-0.50February 2007Tide (m-NAVD)LA (m-NAVD)Figure 2-7. Example comparison of recorded tides (February 2007) at FTB with the ocean tides (LAOH).By analyzing the tidal records for the FTB and LAOH, it is possible to determine the phase lag for lowtide drain-out from the FTB. As shown in Figure 2-7 and Appendix 2-A, there is no discernable phaselag between the high tides in the basin and those in the ocean. The lag of the low tide in the FTBcompared to that in the ocean was approximately 78 minutes on January 19 th 2007 and 114 minutes onJanuary 21st 2008. The low tide lag increased by 36 minutes over the course of the monitoring year asthe flood shoal built.DiscussionThe preliminary engineering studies (M&N 1999) predicted a maximum tidal range of 2.286 m (7.50ft) and a low tide muting of 0.213 m (0.70 ft) in the FTB under the post-construction condition. Thetidal monitoring started on December 21, 2006 so there are no tidal records available for the immediatepost-construction condition (August 26, 2006 through December 20, 2006). The recorded spring lowtides were truncated before January 19, 2007 as described in the tide monitoring methodology. TheFTB experienced a tidal range of 2.266 m (7.44 ft) and a low tide muting of 0.161 m (0.53 ft) inJanuary 19, 2007; and a tidal range of 2.328 m (7.64 ft) and a low tide muting of 0.190 m (0.62 ft) inFebruary 2007. The recorded tides were very close to the predicted values of the post-constructioncondition.By January 2008, the monitoring data show that the FTB experienced a tidal range of 2.280 m (7.48 ft)and a low tide muting of 0.406 m (1.33 ft). Tidal muting predictions in preliminary engineering aseffects of shoaling are for the tide range to reach 2.256 m (7.4 ft) and muting of the low tide to reachMerkel & Associates, Inc. 70