Table 1. Trap maintenance history: Channel Islands Harbor, California. 



Trap dredging dates 





Fill 



Dredge 



Sand volume 



Yearly 









t ime^ 



time-^ 



in trap 



accumulation 









(mo) 



(mo) 



(m3) 



(mVyr) 



June 61 3 







— 



- 



1 278 000 





26 June to 6 



Sept. 



63 



27 



4 



1 518 000 



674 000 



20 Apr. to 19 



Sept. 



65 



24 



6 



2 696 OOO'* 





2 Jan. to 29 



Feb. 



68 



29 



2 



1 278 000 



528 000 



15 Sept. 69 to 6 



Jan. 



70 



22 



4 



2 141 OOO'' 





5 Aug. to 11 



Dec. 



71 



23 



4 



1 835 000 



956 000 



20 Sept. 73 to 23 



Apr . 



74 



28 



7 



1 338 000 



574 000 



8 Sept. to 18 



Dec. 



75 



20 



3 



1 223 000 



732 000 



13 Nov. 77 to 16 



Jan. 



78 



25 



2 



1 835 OOO"* 



463 000^ 



Mar. 80 







26 



- 



1 514 000 



698 poo 



Time in months required for sand trap to fill. 



Time in months needed to dredge trap. 



Initial construction of sand trap completed. 



"^Sand trap enlarged, thus volumes shown are only partially the result 

 of natural filling. 



Accumulation rate as determined from this study. 

 1. Sediment Cores. 



Twenty-eight sediment cores were obtained using standard vibratory coring 

 equipment. Twenty of the cores were taken in the trap area at locations that 

 had been monitored and sampled bimonthly during the previous 18 months as part 

 of the CERC sediment transport study. The remaining eight cores were taken at 

 sites along a beach profile line located about 365 meters north of the trap. 

 This profile is considered a "native beach" profile because it lies far enough 

 updrift to be unaffected by the trap structures and thus provides a location 

 for determining natural beach responses to normal coastal processes. The eight 

 cores were sited by elevation along the profile line. The cores were obtained 

 under private contract and with the assistance of the Naval Civil Engineering 

 Laboratory, Port Hueneme, California. Table 2 contains the following specifics 

 for the 28 cores: location, site elevation, core length, and thickness of 

 sediments affected by erosion and deposition during the previous 18 months. 



Core sites were located using an automatic electronic positioning system. 

 Offshore coring was from a self-propelled crane-barge anchored on location by 

 multiple anchors; a mobile crane was used to position the vibracorer at onshore 

 locations. Vibracoring was to the desired depth as determined by surveyed 

 elevation changes at each site or until the core would no longer penetrate into 

 the substrate (refusal). Refusal occurred only once — at core 19, which was 

 about 1 meter too short — before the desired minimum penetration was achieved. 



