Dredging

2021-22 Dredge Operations

FEDERAL ENTRANCE CHANNEL
Entrance dredging is permitted to commence November 1 each year. Once Twin Lakes is deployed to the entrance, and all equipment is mobilized, entrance dredging operations will continue through April 2022. The typical dredge schedule is Monday – Thursday, with maintenance performed on Fridays.

Prior to transiting the entrance, mariners are still advised to check tide and weather conditions, view the entrance sounding online, and know what your vessel draws. Entrance soundings will be updated periodically during the offseason and posted on the District’s website, here.

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
North harbor dredging is not planned for the 2021-22 season. Crews made significant progress during the 2020-21 dredge season deepening the north harbor turning basin and restoring depths in the fairway and berthing areas utilizing the Port District’s 8″ dredge Squirt.

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.

TwinLakes_Website
Griggs2
DSCN0710
dredgeLittoralDiagram