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

Bolsa Chica Lowlands Restoration Monitoring2007 Annual ReportMuted Tidal Basin FunctionThe flood shoal should be dredged if the tidal drainage in the MTBs is impeded and the MTBfunction is degraded as a result of inefficient drainage. Tidal monitoring in the muted tidal basinwill help determine the dredging trigger related to tidal drainage in the MTBs (Monitoring Teamdetermination).Water qualityTidal circulation in the FTB will be slightly less efficient under the muted tidal condition.However, the FTB should still have an excellent circulation condition with a residence time of afew days. The water quality will degrade if the inlet is closed. At present, the large size of the FTBand the significant wave fetch is believed to be adequate to sustain good water quality even inhighly muted conditions. However, substantial deviations in water quality parameters that suggestisolation from strong oceanic influences should trigger dredging of the flood shoal (MonitoringTeam determination).3.2 TRIGGER ANALYSISAnalysis of Tidal Muting TriggerA review of the tidal ranges in the FTB and LAOH indicates that the differences in the high tideelevations are very small. This implies that the overall measurement is reliable and there is no mutingof the high tides. The low tides are muted and level of muting is due to flood bar accretion in the basin.The muting is similar to what was predicted, with the following specific observations:Tidal muting is positively correlated with tidal range, with greater muting occurring duringspring tides and less muting occurring during neap tides;The trend of tidal muting is for gradually increased muting over time, with the greaterpunctuated increases and reductions in muting that are likely coincident with significantchanges in flow patterns across the flood shoal;The amount of muting shown in Table 2-3 is increasing over the time as the flood shoalexpands and grows in the FTB.Tidal plots in the Appendix 2-A and low tidal muting in Table 2-3 1 show tidal muting on theorder of 0.4 meters (1.31 feet) of the low tide for average spring tides over a period of fourmonths (October 2007 through January 2008).The spring low tide reached -0.155 m (-0.51 ft) in December 2007 and January 2008, whichstill would provide the opportunity for the MTB to drain efficiently.After monitoring of the tides in the muted tidal basin, the dredging trigger related to tidesshould be re-evaluated to provide sufficient drainage in the MTB.Recommendations relating to this dredging trigger are currently considered preliminary in nature asthe muting of the system effects the functioning of the MTBs, which have yet to be opened. As aresult, final dredging triggers relating to tidal muting should only be set after opportunities exist tomonitor the performance of the MTBs under normal and muted conditions. However, preliminaryrecommendations are as follows:Merkel & Associates, Inc. 95