Humboldt Bay current surveys : December 2002-October 2004
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Humboldt Bay current surveys : December 2002-October 2004
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    "At the request of the Humboldt Bay Harbor Recreation and Conservation District and the Humboldt Bay Pilots Association, the National Ocean Service's Center for Operational Oceanographic Products and Services (CO-OPS) conducted a series of current measurements within Humboldt Bay, California, under the auspices of the National Current Observation Program. The local user community reported that the currents differed in strength and timing from the existing published predictions that were referenced to San Francisco Bay Entrance and based on 7 days of 1923 pole data acquired 0.6nm south of Pt. Diablo. Mariners noted strong cross currents at the entrance to Humboldt Bay that tended to 'push' their vessel towards the north jetty during the winter. This first current survey of Humboldt Bay met CO-OPS mission to promote safe navigation and was conducted during the winter when conditions were expected to be most extreme, as requested by the Humboldt Bay Chief Executive Officer. A total of seven stations were occupied during the 2002- 2003 survey: one station outside the harbor and six within the Bay (Figure 1). Prior to the 2002 survey, there were 5 stations within Humboldt Bay referenced to time and speed ratio offsets to SF Bay Entrance. CO-OPS' intention to make a new reference station near the entrance of Humboldt Bay at HB0202 was thwarted when high sediment transport buried the current meter platform and data acquisition was less than the required 30 days. Although the current direction measured at HB0202 did not align with the expected flow between the jetties in the Entrance Channel, the profiler did not malfunction. Current direction recorded at all levels throughout the water column were consistent with the direction of sediment transport and flow reflected off the north jetty and along the shoal just to the north of the profiler's position (Figure 2). Another survey was conducted during the summer of 2004 to measure currents during a relatively quiescent meteorological period when wind and swells were expected to be less intense. Site selection, within the Entrance Channel, was determined from a 12-hour acoustic Doppler current profiler (ADCP) tow where currents displayed the anticipated alignment with the main ship channel and sand movement was expected to be minimal. During this survey, two stations were occupied, one outside the harbor at HB0401 and one between the jetties at HB0402. Development of a new reference station at HB0402, 0.25nm SSE of the north jetty of the Entrance Channel (Figure 3), esulted when nearly 86 days of quality data were collected in 12.8 meters of water. Forty-nine days of data were collected outside the breakwater in 14.1 meters of water. Upon completion of the summer project, data products were generated and new predictions are now available for all stations occupied during the 2002/2003 and 2004 surveys. New reference station daily predictions are available for the remainder of 2005 and will appear in the NOS Tidal Current Tables beginning with the 2006 edition. Due to the limited number of pages in the Tidal Current Tables, the Humboldt Bay stations are listed as secondary stations rather than stand-alone reference stations. All existing stations within Humboldt Bay will be referenced to the new Entrance Channel station. Time differences and speed ratios have been computed and will appear in Table 2 of the 2006 NOS Tidal Current Tables - Pacific Coast of North America and Asia. Raw and quality control (QC) data are available upon request. In addition, harmonic constituents and harmonic-based predictions are available upon request for all stations"--Introduction.
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