U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 6 Station ID: 9415438 PUBLICATION DATE: 01/07/2005 Name: SKAGGS ISLAND, HUDEMAN SLOUGH CA NOAA Chart: 18654 Latitude: 38° 12.3' N ( 38.20500) USGS Quad: CUTTINGS WHARF Longitude: 122° 22.4' W (-122.37300) To reach the tidal bench marks from the intersection of Imola Avenue with State Highway 121/12 in Napa, proceed south on State Highway 121/12 for 6.4 km (4.0 mi) to Duhig Road, then south on Duhig Road for 4.3 km (2.7 mi) to Ramal Road, then west on Ramal Road for 1.8 km (1.1 mi) to Skaggs Island Road, then south on Skaggs Island Road for 2.3 km (1.4 mi) to the Skaggs Island Road bridge over Hudeman Slough. The bench marks are located along the NW side of Skaggs Island Road on the north side of the slough. The tide gauge and staff were on the west side of the wooden bridge spanning Hudeman Slough. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: BM A DESIGNATION: 941 5438 A MONUMENTATION: Bolt VM#: 11807 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Concrete jacket OPUS PID: LATITUDE: 38° 12.3' N ( 38.20500) LONGITUDE: 122° 22.4' W (-122.37300) The primary bench mark is a bolt set on the outer edge of the concrete jacket enclosing one of the wooden support piles on the NW side of the Skaggs Island Road bridge, 35.81 m (117.5 ft) south of the north end of the bridge, and about 2 m (5 ft) below road level.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 6 Station ID: 9415438 PUBLICATION DATE: 01/07/2005 Name: SKAGGS ISLAND, HUDEMAN SLOUGH CA NOAA Chart: 18654 Latitude: 38° 12.3' N ( 38.20500) USGS Quad: CUTTINGS WHARF Longitude: 122° 22.4' W (-122.37300) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 5438 C 1986 DESIGNATION: 941 5438 C MONUMENTATION: Tidal Station disk VM#: 11804 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Stainless steel rod OPUS PID#: BBCY02 LATITUDE: 38° 12.3' N ( 38.20500) LONGITUDE: 122° 22.4' W (-122.37300) The bench mark is a disk set on the NW side of Skaggs Island Road, 1.4 km (0.9 mi) south of the railroad tracks across Skaggs Island Road, 0.2 km (0.1 mi) north of the north end of the Skaggs Island bridge, 9 m (30 ft) NW of a 10 MPH traffic sign, 8 m (27 ft) east of a barbed wire fence, 6 m (21 ft) east of a gas pipeline, and near a pink fiberglass witness post. The bench mark is crimped to the top of a stainless steel rod driven 11.9 m (39 ft) to refusal, and encased in a 4-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 6 Station ID: 9415438 PUBLICATION DATE: 01/07/2005 Name: SKAGGS ISLAND, HUDEMAN SLOUGH CA NOAA Chart: 18654 Latitude: 38° 12.3' N ( 38.20500) USGS Quad: CUTTINGS WHARF Longitude: 122° 22.4' W (-122.37300) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 5438 D 1986 DESIGNATION: 941 5438 D MONUMENTATION: Tidal Station disk VM#: 11805 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Stainless steel rod OPUS PID#: BBCN76 LATITUDE: 38° 12.3' N ( 38.20500) LONGITUDE: 122° 22.4' W (-122.37300) The bench mark is a disk set on the NW side of Skaggs Island Road, 1.37 km (0.85 mi) south of the railrod tracks across Skaggs Island Road, 0.26 km (0.16 mi) north of the north end of the Skaggs Island bridge, 10 m (32 ft) NE of a bend in a gas pipeline, 8 m (27 ft) west of the centerline of Skaggs Island Road, 8.1 m (26.5 ft) east of a barbed wire fence, 7 m (22 ft) NE of the straight section of the pipeline, 4 m (12 ft) west of a short guard rail in front of a bend in the pipeline, and near a pink fiberglass witness post. The bench mark is crimped to the top of a stainless steel rod driven 10.4 m (34 ft) to refusal, and encased in a 4-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 6 Station ID: 9415438 PUBLICATION DATE: 01/07/2005 Name: SKAGGS ISLAND, HUDEMAN SLOUGH CA NOAA Chart: 18654 Latitude: 38° 12.3' N ( 38.20500) USGS Quad: CUTTINGS WHARF Longitude: 122° 22.4' W (-122.37300) T I D A L B E N C H M A R K S BENCH MARK STAMPING: 5438 E 1986 DESIGNATION: 941 5438 E MONUMENTATION: Tidal Station disk VM#: 11806 AGENCY: National Ocean Service (NOS) IDB PID#: SETTING CLASSIFICATION: Stainless steel rod OPUS PID: LATITUDE: 38° 12.3' N ( 38.20500) LONGITUDE: 122° 22.4' W (-122.37300) The bench mark is a disk set on the NW side of Skaggs Island Road, 1.3 km (0.8 mi) south of the railroad tracks across Skaggs Island Road, 0.3 km (0.2 mi) north of the north end of the Skaggs Island bridge, 8 m (26 ft) west of the centerline of Skaggs Island Road, 8 m (26 ft) east of a barbed wire fence, 7 m (23 ft) east of a gas pipeline, and near a pink fiberglass witness post. The bench mark is crimped to the top of a stainless steel rod driven 13.1 m (43 ft) to refusal, and encased in a 4-inch PVC pipe and concrete kickblock.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 6 Station ID: 9415438 PUBLICATION DATE: 01/07/2005 Name: SKAGGS ISLAND, HUDEMAN SLOUGH CA NOAA Chart: 18654 Latitude: 38° 12.3' N ( 38.20500) USGS Quad: CUTTINGS WHARF Longitude: 122° 22.4' W (-122.37300) T I D A L D A T U M S Tidal datums at SKAGGS ISLAND, HUDEMAN SLOUGH based on: LENGTH OF SERIES: 2 MONTHS TIME PERIOD: January 1986 - February 1986 TIDAL EPOCH: 1983-2001 CONTROL TIDE STATION: 9414290 SAN FRANCISCO, SAN FRANCISCO BAY Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS: MEAN HIGHER HIGH WATER MHHW = 1.835 MEAN HIGH WATER MHW = 1.669 MEAN SEA LEVEL MSL = 0.965 MEAN TIDE LEVEL MTL = 0.958 MEAN LOW WATER MLW = 0.247 MEAN LOWER LOW WATER MLLW = 0.000 North American Vertical Datum (NAVD88) Bench Mark Elevation Information In METERS above: Stamping or Designation MLLW MHW BM A 2.788 1.119 5438 C 1986 -0.008 -1.677 5438 D 1986 0.170 -1.499 5438 E 1986 -0.118 -1.787
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 6 of 6 Station ID: 9415438 PUBLICATION DATE: 01/07/2005 Name: SKAGGS ISLAND, HUDEMAN SLOUGH CA NOAA Chart: 18654 Latitude: 38° 12.3' N ( 38.20500) USGS Quad: CUTTINGS WHARF Longitude: 122° 22.4' W (-122.37300) D E F I N I T I O N S Mean Sea Level (MSL) is a tidal datum determined over a 19-year National Tidal Datum Epoch. It pertains to local mean sea level and should not be confused with the fixed datums of North American Vertical Datum of 1988 (NAVD88). NAVD88 is a fixed datum derived from a simultaneous, least squares, minimum constraint adjustment of Canadian/Mexican/United States leveling observations. Local mean sea level observed at Father Point/Rimouski, Canada was held fixed as the single initial constraint. NAVD88 replaces NGVD29 as the national standard geodetic reference for heights. Bench mark elevations relative to NAVD88 are available from NGS through the World Wide Web at National Geodetic Survey. NGVD29 is a fixed datum adopted as a national standard geodetic reference for heights but is now considered superseded. NGVD29 is sometimes referred to as Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological Survey Topographic Quads. NGVD29 was originally derived from a general adjustment of the first-order leveling networks of the U.S. and Canada after holding mean sea level observed at 26 long term tide stations as fixed. Numerous local and wide-spread adjustments have been made since establishment in 1929. Bench mark elevations relative to NGVD29 are available from the National Geodetic Survey (NGS) data base via the World Wide Web at National Geodetic Survey. NAVD88 and NGVD29 are fixed geodetic datums whose elevation relationships to local MSL and other tidal datums may not be consistent from one location to another. The Vertical Mark Number (VM#) and PID# shown on the bench mark sheet are unique identifiers for bench marks in the tidal and geodetic databases, respectively. Each bench mark in either database has a single, unique VM# and/or PID# assigned. Where both VM# and PID# are indicated, both tidal and geodetic elevations are available for the bench mark listed. The NGS's Integrated Data Base (IDB PID) provides geodetic datum based on traditionally leveled and bluebooked ties to the National Spatial Reference System(NSRS) https://www.ngs.noaa.gov/datasheets/. The NGS Online Positioning User Service (OPUS PID) provides geodetic datum based on GPS position & tie it to the NSRS https://www.ngs.noaa.gov/OPUS/. The NAVD88 elevation is shown on the Elevations of Tidal Datums Table Referred to MLLW only when two or more of the bench marks listed have NAVD88 elevations. The NAVD88 elevation relationship shown in the table is derived from an average of several bench mark elevations relative to tide station datum. As a result of this averaging, NAVD88 bench mark elevations computed indirectly from the tidal datums elevation table may differ slightly from NAVD88 elevations listed for each bench mark in the NGS database.