Benchmarks for vertical water levels control
Learn about the purpose of water level gauge benchmarks, and access the tide and water levels benchmark database.
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Benchmarks are the fixed elevation markers against which the 0 setting of the gauge is checked during its operation.
Hydrographic benchmarks landmark the elevation of the benchmarks above chart datum. This is basic to charting and gauging procedures. Only the Canadian Hydrographic Service (CHS) may assign or alter the elevation quoted for a benchmark above chart datum.
Hydrographers can use benchmarks to recover chart datum for future surveys. Surveyors and engineers may relate their surveys and structures to chart datum.
As part of the water level gauge installation procedure, a minimum of 3 benchmarks are established in the immediate vicinity (1/2 km) of the gauge. Benchmarks are unique, as there is never duplication in the same feature or structure.
The elevation difference between the preliminary gauge 0 and each of the benchmarks is then determined by accurate spirit levelling. When the elevation of chart datum is finally chosen in relation to the preliminary gauge 0, the benchmark elevations are:
- recorded in the benchmark descriptions as elevations above chart datum
If the water level gauge is to continue operating, its permanent 0 would be set to chart datum. The benchmarks provide for:
- the recovery of chart datum in future surveys
- consistency in the setting of gauge 0 for all water level measurements at the same site
For additional information on Canadian Hydrographic Service benchmarks contact the regional representative for the area you are interested in.