2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...
2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...
2008 Annual Monitoring Report (pdf 10.9MB) - Bolsa Chica ...
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<strong>Bolsa</strong> <strong>Chica</strong> Lowlands Restoration <strong>Monitoring</strong><br />
<strong>2008</strong> <strong>Annual</strong> <strong>Report</strong><br />
bypass. Rather, it acknowledges that beach erosion is not likely to occur to the extent that would<br />
trigger an obligatory maintenance dredging event for replenishment purposes.<br />
It is more likely that maintenance dredging will be required to address an intrinsic system need related<br />
to the functionality of the MTB tidal control structures. Final triggers to address this issue will need to<br />
be set once all of the MTBs are open to the FTB and have operated under both normal and muted FTB<br />
conditions.<br />
Recommendations<br />
• Modify the expectations of tidal range in the FTB from 2.75 m to 2.29 m, with tidal elevations<br />
ranging from 2.02 m to -0.27 m NAVD.<br />
• Remove the dredge trigger of the Mean Low Tide muting of 0.152 m.<br />
• Add an interim trigger of the rolling average of four consecutive lowest tides achieved during<br />
spring tide series exceeding 0.12 m NAVD, as described above.<br />
• Continue the tidal monitoring program with frequent reporting to show effects of the first<br />
maintenance dredging event occurring in 2009 and to assess the relationship between flood<br />
shoaling and tidal muting.<br />
• Continue the tidal monitoring program to show effects of the first maintenance dredging event and<br />
to assess the relationship between flood shoaling and tidal muting.<br />
• Remove the flood shoal in winter <strong>2008</strong>/2009 as scheduled since effects of the flood shoal impede<br />
the tidal ebbing from the entire site.<br />
• The beach width dredging trigger should be modified to reflect a more current set of beach width<br />
data that includes the effects of the 2002 Surfside-Sunset nourishment. In addition, the trigger<br />
should indicate that dredging should be performed when the beach width is less than two standard<br />
deviations from the mean beach width, since being greater than two standard deviations does not<br />
indicate a need for dredging.<br />
• Consider phasing out the beach width triggers, as these are not likely to ever be tripped prior to<br />
maintenance dredging triggers that address muting and impairment of the MTBs.<br />
• Continue bathymetric monitoring, and anticipate another maintenance dredging event in two years.<br />
3.4 MAINTENANCE DREDGING PLAN<br />
The first maintenance-dredging event occurred in early 2009 based on shoal sediment accumulation<br />
during the first two years post-opening. Since this dredging occurred outside of the present report<br />
window, the details of the dredging program and recommendations for modification of dredging in the<br />
future are to be discussed in the 2009 report. However, it is prudent to make two recommendations at<br />
the present time as they are highly pertinent to maintenance actions and trigger setting.<br />
Merkel & Associates, Inc. 141