Home

Research

        Background

        Objectives

        Beach surveys

        Beach mapping

Contacts

Partners

 

 

 

Oregon Beach and Shoreline Mapping and Analysis Program: Pacific Northwest Estuaries and Shores

Benchmarks

Twenty-five survey monuments were installed in October 2004 along the Rockaway littoral cell.  More recently, the survey network was expanded to include the Neskowin littoral cell, where an additional 8 monuments were installed in February 2006.   The benchmarks consist of either:

  • aluminum sectional rods (A) hammered approximately 12 - 24 ft into the ground and capped with a 2" aluminum cap.  The ends of the rods and caps have been concreted into the ground; or,

  • 2 ft deep holes that include a 4 - 6 ft long galvanized steel earth anchor (with a 6" helix screw) screwed into the hole to provide additional support and rigidity and then backfilled with concrete (B).  These latter benchmarks are characterized by brass survey caps.  All survey caps are stamped with an Oregon Department of Geology designation but currently do not have an ID number on them.

 

Precise coordinates and elevations were determined for the Rockaway beach and shoreline network by the Tillamook County Surveyors Office using several Global Positioning System (GPS) units.  The GPS were mounted on fixed height (2.0 m) survey rods and located over known geodetic survey monuments to establish precise survey control.  Surveys of the new monuments were then undertaken and typically involved occupation times of 20 minutes or more.  This approach enabled multiple baselines to be established from known survey benchmarks points to the unknown monuments, which produced excellent survey control .  Coordinate information for each of the benchmarks were determined in both geographic coordinates and in the Oregon State Plane (northern zone, meters) coordinate system.  All elevations are expressed in the North American Vertical Datum of 1988 (NAVD88).

 

Benchmark coordinates and elevations for the Neskowin cell were undertaken by DOGAMI staff in February 2006.  The approach used is analogous to that described above, with the exception that the surveys involved only two GPS units.  The GPS data were supplemented with information derived from three National Geodetic Survey (NGS) continuously operating reference stations (CORS) that were closest to our study area.  The survey was repeated a second time but at a later date to verify the accuracy of the initial GPS occupations and to identify any survey errors.  This approach yielded horizontal errors that averaged 0.004 mm, while the vertical error was 0.009 mm.

 

To access the benchmark information, please select an area of interest.

 

 

 

  Tillamook County Survey Network:

 

Nehalem Spit 

(Nehalem Bay mouth to Neahkahnie)

 

Rockaway 

(Tillamook Bay to Nehalem Bay mouth)

 

BayOcean Spit 

(Cape Meares to Tillamook Bay mouth)

 

Neskowin 

(Neskowin to Cape Kiwanda)