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

Bolsa Chica Lowlands Restoration Monitoring
2008 Annual Report
• 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.
• Dredge accumulated sands from within the flood shoal in winter 2008/2009 as scheduled since
effects of the flood shoal impede the tidal ebbing from the entire site and adversely effect function
of the MTBs and Freeman Creek Water Control structure.
• 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 and the scheduled 2009
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.
Additional adjustments to dredging triggers are anticipated in response to future performance analysis
of the MTBs and additional analysis of shoaling after the first maintenance dredging cycle is
completed.
The first maintenance-dredging event is scheduled to occur in early 2009. For future dredging events,
consideration should be given to dredging to the permitted depth of the final engineering design depths
to extend the period between maintenance events. Dredging at the time of initial construction was not
completed to full design depths within the maintenance basin. If deepening of the maintenance basin
were completed, this would garner additional time between dredging events and would improve
dredging efficiency by capturing a greater volume of sediment in a more localized and recoverable area
nearer the inlet.
Additionally, the pre-dredging contracting process can consume a considerable period of time and thus
work should be completed to streamline and pre-prepare to the maximum extent practical prior to
maintenance triggers being tripped. This would allow for a reduced period over which the system
functions in an impaired condition prior to completing maintenance dredging. To accomplish this
would require: preparation of the majority of the plans and specifications, completion of permitting
based on a maintenance basin plan and dredge volume range, preparation of bid and contract
documents, and obtaining maximum flexibility for the dredging window of work. Long-term Corps
permits for maintenance dredging are possible, including ten-year permits to include dredging triggers
and pre-dredging notification and approvals that are considerably shorter than applying for a new
permit each time dredging is to be performed.
Merkel & Associates, Inc. 10