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 ...
Bolsa Chica Lowlands Restoration Monitoring 2008 Annual Report Figure 2-16. Long-Term shorezone volume changes, May 1963 to October 2008 Bolsa Chica Monitoring Period Shorezone Volume Changes (2005 to 2008): It is not possible to quantify the shorezone volume changes for the Bolsa Chica Monitoring Period because the October 2005 profile does not extend below the waterline. However, investigation of the time series plots in Appendix 2-D indicates that a trend of shorezone volume loss has prevailed at each transect between January 2007 and October 2008. This may be attributable dispersal of the ebb bar and natural shoreline erosion between Surfside-Sunset nourishment intervals. Beach Width Measurement Time series plots for the beach width measurements obtained at the seven Bolsa Chica area transects by Moffatt and Nichol and at three nearby locations by the U.S. Army Corps of Engineers are presented in Appendices 2-E and 2-F, respectively. The results of the beach width measurements obtained at the seven Bolsa Chica area transects are summarized in Table 2-5. During the two-year period between the January 2007 and December 2008 observations, the MSL beach width decreased at three of the seven sites, increased at three locations, and was essentially unchanged (3 m or less) at the remaining site. In general, the shoreline tended to advance north of the entrance channel and retreat to the south. The greatest shoreline advance was 14 m, and occurred north of the entrance channel at Transects 311+22 and 318+30. The greatest shoreline retreat, 22 m, occurred immediately south of the entrance channel at Transect 333+30, and at the north end of the study area at Transect 249+30. Shoreline change rates during the two-year period ranged from -10.9 m/yr at Transect 249+30 to 8.0 m/yr at Transect 318+30. Merkel & Associates, Inc. 129
Bolsa Chica Lowlands Restoration Monitoring 2008 Annual Report Table 2-5. Beach width measurement program summary statistics, Jan. 2007 to Dec. 2008. Transect Range (m)) Distance to Berm (m) Ave (m) Change (m) Trend (m/yr) Range (m)) MSL Beach Width (m) Ave (m) Change (m) Trend (m/yr) 249+30 57-86 67 -12 -11.7 73-104 85 -22 -10.9 311+22 50-67 59 7 4.0 65-87 75 14 4.5 318+30 56-77 65 9 6.7 69-99 82 14 8.0 333+30 24-46 32 -22 -10.3 38-72 56 -22 -5.7 350+71 22-37 28 -2 -5.9 34-53 47 -3 -2.7 378+29 0-14 3 2 -2.8 6-33 18 6 -2.4 423+89 78-99 85 -3 -0.2 95-110 102 -5 1.4 The Bolsa Chica Monitoring Plan (USFWS, 2001b) defined beach nourishment triggers based on the monthly beach width observations at the Corps measurement sites within the study area. The minimum permitable beach width based on two consecutive monthly measurements was stipulated to be 15.2 m (50 ft). A second condition indicated that the 12-month rolling average beach width could not deviate from the long-term mean beach width (based on the period January 1980 to January 2000) by more than two standard deviations. Table 2-6 shows the beach width statistics for the three Corps measurement sites within the study that were provided in the monitoring plan. Table 2-6. Range and depth of closure at Bolsa Chica area transects. Station Berm Width (m) Range Mean Std. Deviation 247+88 48 - 105 64.0 7.6 307+88 12 - 59 33.2 7.3 424+44 18 - 81 52.4 10.4 Figures 2-17, 2-18, and 2-19 show the long-term rolling average berm width from October 2006 (preproject) to December 2008 at each of the three Corps measurement sites within the study area. The time series plots also show the minimum stipulated berm width (15.2 m), the long-term mean berm width, and a shaded area encompassing two standard deviations above and below the long-term mean berm width. The 12-month rolling average berm width remained above the minimum stipulated berm width (15.2 m) throughout the period at each of the sites. At 307+88 and 424+44, the 12-month rolling average berm width exceeded two standard deviations above the long-term mean. At no location, however, was the 12-month rolling average berm width less than two standard deviations below the long-term mean. Merkel & Associates, Inc. 130
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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 />
Table 2-5. Beach width measurement program summary statistics, Jan. 2007 to Dec. <strong>2008</strong>.<br />
Transect<br />
Range<br />
(m))<br />
Distance to Berm (m)<br />
Ave<br />
(m)<br />
Change<br />
(m)<br />
Trend<br />
(m/yr)<br />
Range<br />
(m))<br />
MSL Beach Width (m)<br />
Ave<br />
(m)<br />
Change<br />
(m)<br />
Trend<br />
(m/yr)<br />
249+30 57-86 67 -12 -11.7 73-104 85 -22 -10.9<br />
311+22 50-67 59 7 4.0 65-87 75 14 4.5<br />
318+30 56-77 65 9 6.7 69-99 82 14 8.0<br />
333+30 24-46 32 -22 -10.3 38-72 56 -22 -5.7<br />
350+71 22-37 28 -2 -5.9 34-53 47 -3 -2.7<br />
378+29 0-14 3 2 -2.8 6-33 18 6 -2.4<br />
423+89 78-99 85 -3 -0.2 95-110 102 -5 1.4<br />
The <strong>Bolsa</strong> <strong>Chica</strong> <strong>Monitoring</strong> Plan (USFWS, 2001b) defined beach nourishment triggers based on the<br />
monthly beach width observations at the Corps measurement sites within the study area. The<br />
minimum permitable beach width based on two consecutive monthly measurements was stipulated to<br />
be 15.2 m (50 ft). A second condition indicated that the 12-month rolling average beach width could<br />
not deviate from the long-term mean beach width (based on the period January 1980 to January 2000)<br />
by more than two standard deviations. Table 2-6 shows the beach width statistics for the three Corps<br />
measurement sites within the study that were provided in the monitoring plan.<br />
Table 2-6. Range and depth of closure at <strong>Bolsa</strong> <strong>Chica</strong> area transects.<br />
Station<br />
Berm Width (m)<br />
Range Mean Std. Deviation<br />
247+88 48 - 105 64.0 7.6<br />
307+88 12 - 59 33.2 7.3<br />
424+44 18 - 81 52.4 10.4<br />
Figures 2-17, 2-18, and 2-19 show the long-term rolling average berm width from October 2006 (preproject)<br />
to December <strong>2008</strong> at each of the three Corps measurement sites within the study area. The<br />
time series plots also show the minimum stipulated berm width (15.2 m), the long-term mean berm<br />
width, and a shaded area encompassing two standard deviations above and below the long-term mean<br />
berm width.<br />
The 12-month rolling average berm width remained above the minimum stipulated berm width<br />
(15.2 m) throughout the period at each of the sites. At 307+88 and 424+44, the 12-month rolling<br />
average berm width exceeded two standard deviations above the long-term mean. At no location,<br />
however, was the 12-month rolling average berm width less than two standard deviations below the<br />
long-term mean.<br />
Merkel & Associates, Inc. 130
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