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The City of Eugene Code Chapter 7.087 (2) states the City Engineer shall place bench marks on all lines run with a level for establishing streets, grades, levels, sewers and drains.
The City’s last update to the Bench System was in June of 1974. Over the course of time, the City's Bench Mark system has become outdated. Many of the original bench marks were destroyed and, as the City of Eugene grew, very little vertical control was established in much of the outlying areas. For these reasons, the City decided to update the vertical control network during the summer of 2001. As time passes and additional Bench Marks are needed, the City will add to this network and addendums will be issued.
All elevations are on the 1929 National Geodetic Vertical Datum (NGVD 1929 Datum). Two base bench marks were used for the City Datum. The first control bench is "449 (USGS)" at Eugene , on the Campus of the University of Oregon, on the northeast corner of Villard Hall, in the North face of the building, 2 inches below the date "1885" and stamped "449B1903" Elevation 449.320. The second control bench is X94 (USC & GS) at Eugene, on the Southern Pacific Company Railroad Station Building at the north end of 5th Avenue, in the center of the curved wall (north side of building) facing the track, about 3.5 feet above the pavement stamped "X94 1931" Elevation 430.993.
Monuments set in the 2001 update are 3" brass caps stamped:
CITY OF EUGENE
With the 2001 update, most bench marks set on fire hydrants, power poles and scribed marks on structures within private property have been removed. A few elevation errors were found on existing bench marks (not all bench marks were reshot) from the 1974 publication, these elevations have been revised to reflect the new elevations. Also, note that in some parts of town (near west side, Bethel Danebo) expansive soils exist and can produce annual variations in Bench Marks up to 0.10 feet.
A Leica NA2002 digital level was used for these new level circuits. The goal was first order accuracy of Â±0.02 vM, where M is the miles in the circuit. It was found that, by carefully following a set procedure and keeping shots within 150 feet, this accuracy was generally attainable. However, these elevations are not considered to be "First Order", as all procedures for First Order levels were not followed in all loops.
In 2012 the City of Eugene calculated the vertical adjustment to create elevations for their benchmark on the NAVD 88 vertical datum. Ten benchmarks located within the Urban Growth Boundary of Eugene were used in the adjustment study. All ten of the benchmarks used in the analysis where also within the National Geodetic Survey database.
Using the National Geodetic Survey computer program “Vertcon” the calculated difference between NGVD 29 and NAVD 88 is 3.61’. In the analysis of the common benchmarks between the City of Eugene and the National Geodetic Survey database the actual difference is 3.87’. Therefore, all City of Eugene benchmarks within the City of Eugene Urban Growth Boundary with a NAVD 88 elevation have been established by adding an adjustment factor of +3.87 feet in elevation from the previous established elevation being an NGVD 29 based elevation.