2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...

Bolsa Chica Lowlands Restoration Monitoring
2008 Annual Report
bypass. Rather, it acknowledges that beach erosion is not likely to occur to the extent that would
trigger an obligatory maintenance dredging event for replenishment purposes.
It is more likely that maintenance dredging will be required to address an intrinsic system need related
to the functionality of the MTB tidal control structures. Final triggers to address this issue will need to
be set once all of the MTBs are open to the FTB and have operated under both normal and muted FTB
conditions.
Recommendations
• Modify the expectations of tidal range in the FTB from 2.75 m to 2.29 m, with tidal elevations
ranging from 2.02 m to -0.27 m NAVD.
• Remove the dredge trigger of the Mean Low Tide muting of 0.152 m.
• Add an interim trigger of the rolling average of four consecutive lowest tides achieved during
spring tide series exceeding 0.12 m NAVD, as described above.
• Continue the tidal monitoring program with frequent reporting to show effects of the first
maintenance dredging event occurring in 2009 and to assess the relationship between flood
shoaling and tidal muting.
• Continue the tidal monitoring program to show effects of the first maintenance dredging event and
to assess the relationship between flood shoaling and tidal muting.
• Remove the flood shoal in winter 2008/2009 as scheduled since effects of the flood shoal impede
the tidal ebbing from the entire site.
• The beach width dredging trigger should be modified to reflect a more current set of beach width
data that includes the effects of the 2002 Surfside-Sunset nourishment. In addition, the trigger
should indicate that dredging should be performed when the beach width is less than two standard
deviations from the mean beach width, since being greater than two standard deviations does not
indicate a need for dredging.
• Consider phasing out the beach width triggers, as these are not likely to ever be tripped prior to
maintenance dredging triggers that address muting and impairment of the MTBs.
• Continue bathymetric monitoring, and anticipate another maintenance dredging event in two years.
3.4 MAINTENANCE DREDGING PLAN
The first maintenance-dredging event occurred in early 2009 based on shoal sediment accumulation
during the first two years post-opening. Since this dredging occurred outside of the present report
window, the details of the dredging program and recommendations for modification of dredging in the
future are to be discussed in the 2009 report. However, it is prudent to make two recommendations at
the present time as they are highly pertinent to maintenance actions and trigger setting.
Merkel & Associates, Inc. 141