This information is not intended for navigational purposes.
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Please recognize the U.S. Geological Survey (USGS) and the Southwest Washington Coastal Erosion Study (SWWCES) as the source of this information.
Water depth relative to NAVD88 was calculated by first determining the primary tidal station used for a particular survey. This information was obtained from original smooth sheets and/or descriptive reports where possible, or assumed where such information didn't exist. Relative offsets between MLLW and NAVD88 at each tidal station was determined based on geodetic information provided for NOS benchmarks, determined by independent geodetic surveys conducted by the Department of Ecology, or estimated where no other information was available. The NAVD88 values were thus calucalated by adding the relative differences between datums to the MLLW depth values. In some cases, a larger datum correction was applied to offset obvious bias in the original data set. An in-depth description of the methodolgy employed for these conversions, along with a discussion of specific corrections, are available in Buijsman, et al., 2002.
DATA SET SPECIFIC INFORMATION: For the data set: h4728_1927 The primary tidal station used is: Pt. Grenville The source used to determine the tidal station: USC&GS Descriptive Report The vertical datum relative to NAVD88 is: -0.36 meters The conversion applied to charted depths: -0.36 meters
12 points were given a cartographic code of 999 because of apparent erroneous values. There is quite a bit of variation in sounding depths offshore. Not all potentially spurios data were identified. 722 points were given a a cartographic code of 888, where soundings overlapped with surveys H4710 and H4621 (>1m differences) and H4620 (~1-2m differences).
Only soundings with a cartographic code of 711 should be used for analysis.