Dredging

2017-18 Dredge Operations

FEDERAL ENTRANCE CHANNEL
Crews deployed Twin Lakes and began dredging the federal entrance channel on November 13, 2017. Entrance channel dredging operations will continue through April 2018. The typical dredge schedule is Mondays – Thursdays, with maintenance performed on Fridays.

During dredging operations, pass Twin Lakes on the east side (Crow’s Nest side) of the channel unless otherwise marked. Stay at least 50′ from the dredge. Contact the crew for passing instructions on VHF channel 8.

 

NORTH HARBOR DREDGING
On October 2, 2017crews began operating Twin Lakes in the north harbor to dredge the material shoaling the turning basin, X-J channel and culvert area. After several weeks of dredging the north harbor with Twin Lakes, crews moved Twin Lakes to the south harbor in preparation for entrance channel dredging. Crews are utilizing Squirt for the remainder of north harbor dredging.

The Science Behind Dredging

WHY WE DREDGE
Dredging of the harbor is required because of the constant easterly movement of sand along our coast and thus, across our harbor entrance. Such movement is generated by the ongoing forces of waves and currents. The amount of material moved and deposited is directly proportional to the severity of current and wave conditions. This constant movement of masses of sand is termed littoral drift.

Sand indicated by orange dotted areas, is carried down the San Lorenzo River and thence moved down-coast by wave and tidal action called littoral drift. Constantly moving, the sand mass builds up against the west jetty and flows around it, shoaling the Santa Cruz Harbor entrance channel. Impeding sand is then dredged from the entrance channel and deposited in the inter-tidal zone where the existing littoral drift carries it down-coast, nourishing those beaches east of the Santa Cruz Harbor entrance.

THE DANGER OF SHOALING
Because of sand incursion at the mouth of the harbor, it is essential that an annual dredging effort be maintained to assure sufficient depth at the harbor entrance to permit the safe passage of vessels transiting the entrance. Shoaling conditions caused by littoral sand drift produce dangerous and unpredictable breaking wave formations at the harbor’s entrance. These breaking waves are extremely hazardous to incoming, and outgoing vessels and pose a particular danger to individuals walking on either of the jetties.

 

Dredging Scientific Studies & Reports

 

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