2007 Annual Monitoring Report (pdf 16MB) - Bolsa Chica Lowlands ...

Bolsa Chica Lowlands Restoration Monitoring2007 Annual ReportTable 2-2. Change in sediment volumes between surveys and rate of sediment accretion.Change in Sediment VolumeSurvey date range Time cubic meters cubic yards cubic meters/dayfrom Aug '06 to Jan '07 148 days + 90,311 + 118,122 + 610from Jan '07 to June '07 159 days + 66,219 + 86,611 + 416from June '07 to Jan '08 197 days +40,675 + 53,201 +206from Aug '06 to Jan '08 504 days + 197,692 + 258,571 + 392Figure 2-4 presents the accretion rate graphically as sediment accretion per month within the surveyarea indicated in Figure 2-1. The initial large input of sand between the basin opening and the January2007 survey was 90,311 m 3 over a roughly 5 month period, for an average of 18,062 m 3 /month. Therate of accretion dropped between January and June 2007 to 13,244 m 3 /month and slowed even morebetween June 2007 and January 2008 to 6,779 m 3 /month. It may be useful in the future to comparewhole calendar years to one another. The accretion rate from January 2007 to January 2008 was anaverage of 8,948 m 3 /month or an average of 301 m 3 /day. Again, the averages do not represent theactual accretion per day or month, as deposition and erosion occurred throughout the period at anuneven rate.Sediment Accretion Rate per MonthAccretion Rate (m 3 /month)2000015000100005000018,062 m 3 /moOpening thru Jan. 2007(5 month period)Figure 2-4. Sediment accretion rate per month.13,244 m 3 /moJan. 2007 thru June 2007(5 month period)6,779 m 3 /moJune 2007 thru Jan. 2008(6 month period)DiscussionThe bathymetry survey of the FTB basin near the tidal inlet and numerous site visits indicate that thetidal inlet morphology and sediment depositional areas (inlet thalweg and flood shoal patterns) arehighly dynamic due to dynamic tidal and sedimentation processes. The January 2007 survey showsthat the inlet thalweg was in the middle of the inlet channel and the shoal was on the southeast side ofthe inlet channel as shown in Figure 2-1. This reflects the infancy state of the wetland geomorphologyat that time, with sediment not yet having deposited along the inside bank of the tidal inlet channel.Merkel & Associates, Inc. 64