Wednesday, October 22, 2014

NOLA Benchmarks

In 1910, the New Orleans Sewerage and Water Board established a new system of permanent benchmarks that replaced a temporary one. The older system had consisted of 6" galvanized iron boat spikes driven horizontally into the city's trees at a height 30" above the ground. This system proved perishable and the board decided to establish permanent benches consisting of granite monuments weighing approximately 200 pounds that were set into larger blocks of concrete.

Assistant engineer C.B. Adams spearheaded the modernization, selecting sites in public squares, major thoroughfares and parks. All elevations indicated on the benchmarks referenced Cairo Datum taken from the old Metairie Ridge Stone, which had been set in 1869 on the lake side of the Rampart Street neutral ground on the lower side of Canal Street.

New Orleans surveyor Guy Seghers retained the board's publication, Pocket Edition of System of Permanent Bench Marks for the City of New Orleans (31 December 1910) and revised it as certain benchmarks were voided or if elevations significantly changed. Benchmark 46-B, set April 1910 in the drainage pumping station at the intersection of Florida and Jourdan Avenues, originally recorded an elevation of 24.217, but Seghers noted a corrected elevation of 22.55.

Seghers' Pocket Edition includes a complete inventory of all the 1910 benchmarks, as well as a locator map.

Map and Regulation Bench Mark above from:  Pocket Edition of System of Permanent Bench Marks for the City of New Orleans (31 December 1910). New Orleans: Sewerage and Water Board, 1910. Southeastern Architectural Archive, Special Collections Division, Tulane University Libraries.

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