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

Bolsa Chica Lowlands Restoration Monitoring
2008 Annual Report
120
12-Month Rolling Average Berm Width (m)
100
80
60
40
20
long-term mean = 52.4 m
minumum permitable beach width
+-2 Standard Deviations
from Long-Term Mean
0
2005 2006 2007 2008 2009 2010
Year
Figure 2-19. Twelve-Month average berm width at Corps Station 424+44
Influence of Entrance Channel
Shoreline Changes Adjacent to Entrance Channel: Between October 2005 and October 2008, the
beaches upcoast (north) of the new entrance channel accreted, while those downcoast (south) of the
channel tended to erode (Figure 2-13). Figure 2-20 compares the shoreline changes immediately north
of the channel (Transect 318+30) with the changes for the remaining upcoast monitoring sites
(Transects 249+30 and 311+12). The shoreline at the three upcoast transects responded similarly
between October 2005 and January 2007. Following the opening of the new channel (January 2007 to
October 2007), the shoreline at Transect 318+30 retreated slightly, while the beaches at the other
upcoast sites advanced. Between October 2007 and October 2008, the shoreline advanced at Transect
318+30, stabilized at Transect 311+12, and retreated at Transect 249+30.
A time series of the shoreline changes at the four transects located downcoast (south) of the entrance
channel is shown in Figure 2-21. The shoreline changes at Transect 333+30 (immediately downdrift of
the channel) were nearly identical to those at Transects 350+71 and 423+89, and indicate a trend of
shoreline retreat between October 2005 and October 2007. The shoreline changes at Transect 378+29
differed only modestly. During the most recent one-year period (October 2007 to October 2008),
modest shoreline advance occurred at the two transects nearest the entrance channel (333+30 and
350+71). In contrast, the shoreline retreated at the remaining sites.
Volume Changes Adjacent to Entrance Channel: The subaerial volume changes upcoast of the
entrance channel (Figure 2-22) responded similarly to the shoreline changes. The subaerial volume
increased during the three-year period at each of the sites, with the most pronounced gains occurring at
Transects 311+22 and 318+30.
Merkel & Associates, Inc. 132