4.2 Measurements from a Datum_Plane
|
Levels measured above a datum_plane are recorded as negative values. Levels measured below a datum_plane are recorded as positive values. |
Examples
- The head of a flowing artesian bore measured as 10m above the ground surface is reported as -10.
- The depth to the watertable measured as 10m downhole from the top of the casing is reported as 10.
- The depth to the top of the screen at 55m relative to the ground surface is reported as 55.
This convention is consistent with other standards such as ASTM D5409 and is also used to describe changes in levels. A change that results in the level being lower than previously is recorded as a positive value, a change that results in the level being higher is recorded as a negative value. Hence the lowering of water levels during an aquifer test (ie. drawdown) is recorded as a positive value.
|
