U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Datums Page Page 1 of 5 PUBLICATION DATE: 09/27/1983 Station ID: 9418983 SUPERCEDED DATE: 04/21/2003 Name: UPPER MAD RIVER SLOUGH, HUMBOLDT BAY CALIFORNIA NOAA Chart: 18622 Latitude: 40° 47.8' N USGS Quad: ARCATA SOUTH Longitude: 124° 7.1' W To reach the tidal bench marks from U.S. Highway 101 exit at Arcata/Samona Boulevard west, right on K Street which turns into Alliance Road, continue 1 mile (1.6 km) on Alliance Road until it ends at a T-intersection, left turn and continue 0.5 mile (0.8 km) to Lanphere Road then left on Lanphere Road for 1.5 miles (2.4 km). The bench marks are along Lanphere Road east of the ranch buildings. The tide gage and staff were located on the south side of and at the midpoint of the bridge over the slough. T I D A L B E N C H M A R K S PRIMARY BENCH MARK STAMPING: 8983 A 1978 MONUMENTATION: Survey Disk VM#: 8749 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is 30.0 feet (9.1 m) east of the east end of the Lanphere Road bridge over the slough, 8.0 feet (2.4 m) south of the centerline of Lanphere Road, 4.0 feet (1.2 m) east of a witness post/telephone pole and 0.1 foot (0.03 m) below grade. The bench mark is on a rod driven to 32.0 feet (9.8 m) and encased in concrete. BENCH MARK STAMPING: 8983 B 1978 MONUMENTATION: Survey Disk VM#: 8750 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is 370.0 feet (112.8 m) east of the east end of Lanphere Road bridge over the slough, 92.0 feet (28.0 m) west of the second telephone pole east of the east end of the bridge, 11.5 feet (3.5 m) south of the centerline of Lanphere Road, 2.0 feet (0.6 m) north of a witness post, and 0.4 foot (0.1 m) below grade. The bench mark is on a rod driven to 32.0 feet (9.8 m) and encased in concrete.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 2 of 5 PUBLICATION DATE: 09/27/1983 Station ID: 9418983 SUPERCEDED DATE: 04/21/2003 Name: UPPER MAD RIVER SLOUGH, HUMBOLDT BAY CALIFORNIA NOAA Chart: 18622 Latitude: 40° 47.8' N USGS Quad: ARCATA SOUTH Longitude: 124° 7.1' W T I D A L B E N C H M A R K S BENCH MARK STAMPING: 8983 C 1978 MONUMENTATION: Survey Disk VM#: 8751 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is 528.0 feet (160.9 m) east of the east end of Lanphere Road bridge over the slough, 175.0 feet (53.3 m) WSW of the intersection of the level dirt road and Lanphere Road, 25.0 feet (7.6 m) SW of a sign ONE LANE BRIDGE, 10.0 feet (3.0 m) south of the centerline of Lanphere Road, 4.0 feet (1.2 m) north of a witness post, and 0.1 foot (0.03 m) below grade. BENCH MARK STAMPING: 8983 D 1978 MONUMENTATION: Survey Disk VM#: 8752 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is 0.17 mile (0.27 km) east of the east end of the Lanphere Road bridge over the slough, 51.0 feet (15.5 m) SE of the center of the intersection of the levee dirt road and Lanphere Road, 19.0 feet (5.8 m) south of the center of Lanphere Road, 2.5 feet (0.8 m) south of a witness post, and 0.1 foot (0.03 m) below grade. The bench mark is on a rod driven to 54.0 feet (16.5 m) and encased in concrete and a PVC pipe.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 3 of 5 PUBLICATION DATE: 09/27/1983 Station ID: 9418983 SUPERCEDED DATE: 04/21/2003 Name: UPPER MAD RIVER SLOUGH, HUMBOLDT BAY CALIFORNIA NOAA Chart: 18622 Latitude: 40° 47.8' N USGS Quad: ARCATA SOUTH Longitude: 124° 7.1' W T I D A L B E N C H M A R K S BENCH MARK STAMPING: 8983 E 1978 MONUMENTATION: Survey Disk VM#: 8753 AGENCY: PID: SETTING CLASSIFICATION: Galvanized Steel Rod The bench mark is 0.2 mile (0.3 km) east of the east end of the Lanphere Road bridge over the slough, 60.0 feet (18.3 m) east of the fourth telephone pole east of the east end of the bridge, 10.5 feet (3.2 m) south of the centerline of Lanphere Road, 3.0 feet (0.9 m) north of a witness post, and 0.1 foot (0.3 m) below grade. The bench mark is driven to 65.0 feet (19.8 m) and encased in concrete.
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 4 of 5 PUBLICATION DATE: 09/27/1983 Station ID: 9418983 SUPERCEDED DATE: 04/21/2003 Name: UPPER MAD RIVER SLOUGH, HUMBOLDT BAY CALIFORNIA NOAA Chart: 18622 Latitude: 40° 47.8' N USGS Quad: ARCATA SOUTH Longitude: 124° 7.1' W T I D A L D A T U M S Tidal datums at UPPER MAD RIVER SLOUGH, HUMBOLDT BAY based on: LENGTH OF SERIES: 5 MONTHS TIME PERIOD: AUGUST-DECEMBER 1978 TIDAL EPOCH: 1960-1978 CONTROL TIDE STATION: 9419750 CRESCENT CITY Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in FEET: HIGHEST OBSERVED WATER LEVEL (12/28/1978) = 9.46 MEAN HIGHER HIGH WATER MHHW = 7.93 MEAN HIGH WATER MHW = 7.22 MEAN TIDE LEVEL MTL = 4.26 MEAN LOW WATER MLW = 1.30 MEAN LOWER LOW WATER MLLW = 0.00 LOWEST OBSERVED WATER LEVEL (12/31/1978) = -2.22 Bench Mark Elevation Information In FEET above: Stamping or Designation MLLW MHW 8983 A 1978 14.28 7.06 8983 B 1978 10.89 3.67 8983 C 1978 12.25 5.03 8983 D 1978 12.88 5.66 8983 E 1978 13.46 6.24
U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration National Ocean Service Page 5 of 5 PUBLICATION DATE: 09/27/1983 Station ID: 9418983 SUPERCEDED DATE: 04/21/2003 Name: UPPER MAD RIVER SLOUGH, HUMBOLDT BAY CALIFORNIA NOAA Chart: 18622 Latitude: 40° 47.8' N USGS Quad: ARCATA SOUTH Longitude: 124° 7.1' W 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 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.