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 ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
<strong>Bolsa</strong> <strong>Chica</strong> Lowlands Restoration <strong>Monitoring</strong><br />
<strong>2008</strong> <strong>Annual</strong> <strong>Report</strong><br />
III. MAINTENANCE DREDGING PROGRAM<br />
The maintenance dredging program is planned as a sand management action to maintain “no net loss”<br />
of sand to the downcoast beaches as required in the EIR/EIS and project permits, as well as to ensure<br />
the vitality of the tidal system. During regular maintenance dredging operations, sand will be removed<br />
from the flood shoal of the FTB within the original dredging footprint, in a region that can extend from<br />
the tidal inlet north to approximately the position of the Freeman Creek culvert. The final area may be<br />
slightly larger or smaller depending on shoaling patterns determined from pre-dredge surveys. Sand<br />
dredged from the basin will be placed at the beach or nearshore areas based on the results of beach<br />
monitoring as well as a consideration of the volume of material to be dredged.<br />
Preliminary engineering studies (M&N 1999) and the Basis of Design <strong>Report</strong> (M&N 2003) estimated<br />
the quantity of sand that would accrete in the lagoon would be on the order of 126,000 m 3 (165,000<br />
yd 3 ) during the first year, 102,000 m 3 (134,000 yd 3 ) during the second year, 49,000 m 3 (64,000 yd 3 )<br />
during the third year, and 7,600 m 3 (10,000 yd 3 ) during the fourth year post opening. The reduced<br />
sand influx rate in later years was predicted as a result of anticipated system muting. Therefore, the<br />
need for maintenance dredging would arise before later low influx rates would be realized.<br />
Maintenance dredging plans included provisions for dredging deeper than the original dredge depth but<br />
within originally permitted dredge depths. This could add as much as 400,000 m 3 (550,000 yd 3 ) of<br />
dredging to maintenance sand removals from the FTB. This additional advance maintenance quantity<br />
would provide a longer interval between dredging cycles if it were implemented.<br />
3.1 DREDGING TRIGGERS<br />
The following parameters were monitored and analyzed to evaluate the functioning of the system and<br />
determine when dredging should be performed. Some of these parameters have previously established<br />
dredging triggers associated with them, as indicated, while others have thresholds that were established<br />
by the monitoring team, based on the need to sustain the biological and hydrological functioning of the<br />
system.<br />
Tidal Muting<br />
Muting of the average low tide elevations (Mean Low Water) on the order of 0.5 feet would<br />
indicate that the flood shoal maintenance dredging was warranted (Biological <strong>Monitoring</strong> and<br />
Follow-up Plan [USFWS 2001]).<br />
Muted Tidal Basin Function<br />
The flood shoal should be dredged if the tidal drainage in the MTBs is impeded and the MTB<br />
function is degraded as a result of inefficient drainage. Tidal monitoring in the FTB will help<br />
determine the dredging trigger related to tidal drainage in the MTBs (<strong>Monitoring</strong> Team<br />
determination).<br />
Beach Width<br />
Flood shoal dredging should occur if any beach is found to be narrower than 50 feet, based on two<br />
consecutive monthly beach width measurements, and/or if any 12-month rolling average of beach<br />
widths which deviate more than 2 standard deviations from the mean beach width, using the 20-<br />
year historic record to establish these means and standard deviations (Beach <strong>Monitoring</strong> Plan<br />
[USFWS, 2001]).<br />
Merkel & Associates, Inc. 136