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 />
surveys, the method provides a cost-effective means to supplement the more accurate MSL beach<br />
widths derived from the semi-annual beach profile survey data.<br />
Results<br />
The beach profile plots are provided in Appendix 2-B. MSL beach widths and sediment volume data<br />
are presented in Appendices 2-C and 2-D, respectively. Appendix 2-E contains the beach width<br />
measurements obtained for the <strong>Bolsa</strong> <strong>Chica</strong> monitoring program, while Appendix 2-F contains those<br />
collected by the U.S. Army Corps of Engineers.<br />
Beach Profile Plots<br />
The <strong>2008</strong> beach profile data were used in conjunction with data from the historical surveys to create<br />
profile plots and compute changes in beach width and sediment volume. The beach profile plots<br />
developed from the survey data are provided in Appendix 2-B. The range on each profile plot<br />
represents the distance in meters seaward of the survey origin measured along the transect alignment.<br />
The elevation is given in meters relative to NAVD88.<br />
Two sets of beach profile plots were generated for each transect. The first set of plots shows all of the<br />
beach profile data available for each transect, while the second set of plots shows only those profiles<br />
obtained in during the three-year period encompassing the end of construction of the <strong>Bolsa</strong> <strong>Chica</strong><br />
Lowlands Restoration Project and the first two years post-construction (October 2005 to October<br />
<strong>2008</strong>). The plots focusing on the recent three-year period also show the envelope of all available<br />
profile data that preceded the opening of the <strong>Bolsa</strong> <strong>Chica</strong> entrance channel in August 2006 (May 1963<br />
to March 2006). These plots also include two panels for each transect - one isolating the nearshore<br />
region of the profile and another displaying the entire profile length.<br />
Mean Sea Level Beach Widths<br />
Mean Sea Level (MSL) beach widths are provided in Appendix 2-C. The beach width was computed<br />
as the horizontal distance, in meters, between the landward edge of the beach sand and the point at<br />
which the beach profile intersected the plane of MSL Datum. In the <strong>Bolsa</strong> <strong>Chica</strong> area, MSL lies 0.79<br />
m above NAVD88. Notwithstanding the use of NAVD88 as the elevation reference for the profile<br />
data, MSL was adopted as the shoreline reference in the belief that it provides a more accurate<br />
indicator of changes in beach configuration.<br />
Sediment Volumes<br />
Sediment volume changes are provided in Appendix 2-D. The volume changes were computed along<br />
each transect for the entire width of the shorezone, and for that portion of the profile located above<br />
MSL (subaerial volume).<br />
The offshore boundary of the control volume for the beach above MSL was placed at the intersection<br />
of the profile and a horizontal line corresponding to the elevation of MSL. The offshore boundary for<br />
the shorezone was placed at the “statistical range of closure”. This parameter represents the distance<br />
seaward of the transect origin, beyond which profile variations are smaller than the accuracy of the<br />
survey technique. As implied by its definition, the statistical range of closure was adopted as the<br />
offshore boundary to separate the signal of true profile change from the noise of survey inaccuracy.<br />
The sea bottom elevation at the range of closure corresponds to the “depth of closure” or the depth at<br />
which sediment transport is not substantially affected by littoral processes.<br />
The statistical range of closure was determined for the five historical transects as part of the CCSTWS-<br />
OC. However, these boundaries were no longer appropriate due to the profile changes that resulted at<br />
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