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

Bolsa Chica Lowlands Restoration Monitoring
2008 Annual Report
abandoned. Of these, 174 total chicks were produced in 2008 and a minimum of 57 and a maximum of
109 (32.8 to 62.6%) chicks survived to fledge. The minimum fledgling estimate per nest (0.85
fledglings/nest) is slightly below the average (0.95 fledglings/nest) of the study years. The maximum
estimate of fledglings per nest (1.62 fledglings/nest) would exceed the previous high of 1.47 in 2005.
Avian monitoring recommendations include continuing the Belding’s Savannah sparrow monitoring
program to include a minimum of 2 surveys per breeding season and implementation of the
management recommendations detailed in the snowy plover report (Appendix 1-F).
INLET FLOOD SHOAL
The rate and distribution of sand accretion in the FTB inlet was assessed by bathymetric survey in
January and June 2007, and in January, July, and December 2008. The volume and distribution of
accumulated sand was compared to the pre-basin opening conditions of August 2006. A small shoal
had formed in the inlet by January 2007 and continued to expand through 2007 and 2008. The net
volume of sediment (composed entirely of littoral sand) accreted within the assessment polygon was
compared to the pre-opening conditions and had reached 204,923 m 3 by December 2008. This can be
expressed as a total rate of volume change from the basin opening through December 2008, roughly 28
months later, of approximately 240 m 3 /day. It is important to note, however, that this average rate
does not represent the actual accretion per day, as deposition and erosion occurred throughout the
period at an uneven rate.
To examine this variable rate, the contour plots of each survey were compared to each other to quantify
areas of erosion and accretion between surveys. As anticipated, there was a large input of sand
between the basin opening on August 24, 2006 and the first survey on January 19, 2007, with an
average of 402 m 3 /day. The influx rate then decreased between subsequent surveys, to an average of
230 m 3 /day in 2007 and 134 m 3 /day in 2008.
The flood shoal volume, area of shoaling, and shoaling rate have occurred similarly to processes
predicted during the project design. The variable seasonal influx of sand, and added complication of
provision of local source sand in the pre-filled ebb bar and beach around the mouth, is expected to
have played a role in the high early infill rates. Further, early infill would have also added sand to the
oversized entrance channel, thus decreasing the observed rate of shoaling from the true rate since the
flood shoal survey assessment area does not extend out fully into the entrance channel. Subsequent
reduced rates of infill may indicate more rapid achievement of relative stability following the initial
system loading.
Future monitoring of the flood shoal will occur in January and June of 2009 and 2010.
TIDAL MONITORING
Accretion of sand within the flood shoal of the FTB is the most important factor causing tidal lag and
muting. Tidal monitoring provides a means of tracking the lag and muting and providing information
necessary to determine the need for maintenance dredging to ensure proper physical and ecological
system functioning.
Tidal monitoring began in the FTB in December 2006 and was continuous throughout 2008.
Comparison of the lower low tide data for each day showed that the FTB did not completely drain to
local oceanic sea levels (as measured at Los Angeles Outer Harbor [LAOH]) during lower low spring
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