Concepts – Water Level Depth to Elevation Conversions

Concepts – Water Level Depth to Elevation Conversions - Overview

To perform analysis of water levels, all water levels need to be converted to an elevation in either masl (metres above sea level) or fasl (feet above sea level).  When populating the database, however, the data can be entered as a mixture of masl or fasl or depth to water.  SiteFX will convert all values to a consistent set of elevations in either masl or fasl.

 

Note: Water levels are often recorded as depth to water in either metres or feet. The depth is measured relative to a known elevation such as the top of pipe, top of casing, ground surface, or an alternative point. SiteFX will convert these values to elevations.

 

Note: SiteFX never overwrites the original values and units that you enter.  These values are stored in the ouom (original unit of measure) fields.

 

 

image

The Conversions Form

Water level conversions occur using the following methodology. Note that the order of these steps are important as each subsequent step attempts to fill in the elevation if the previous step did not obtain it.

1.        If the user has chosen to ‘Re-convert all data’, the value and unit are nullified if the ouom value is not null and ouom unit are one of the following:

ftbref, fbref, fbtop, fbtoc, f, ft, feet, fbgs, mbref, mbtop, mbtoc, m, metres, meters, meter, metre, mbgs

Note – if the user has chosen ‘Convert new data only’ then this step is skipped.

2.        SiteFX checks what final units (masl or fasl) the user wants to use. This is set in SiteFX from the Tools > Options menu. 

3.        Original values/units get converted to an elevation by subtracting from the reference elevation (if it exists) as long as the wl date is between the reference elevation start date and end date.  If the reference elevation end date is missing, it assumed that the reference elevation is still valid today.  This operation is done only where the water level elevation field is currently blank. If the location is an angled borehole, the dip is also used. Records that are affected have the following ouom units:

mbref, mbtop, mbtoc, m, metres, meters, meter, metre, fbref, fbtop, fbtoc, f, ft, feet, ftbref

4.        If the reference elevation was missing, the ground elevation is used.  Records that are affected have the following units:

mbref, mbtop, mbtoc, m, metres, meters, meter, metre, mbgs,  fbref, fbtop, fbtoc, f, ft, feet, ftbref, fbgs

5.        As a last step, if both ground elevation and reference elevation are missing, we move the depth to water over, so at least the user knows the data is present when viewing through SiteFX. Unit used is ‘mbref’ (metres below reference) or ‘fbref’ (feet below reference). Records that are affected have the following unit:

mbref, mbtop, mbtoc, m, metres, meters, meter, metre, mbgs, fbref, fbtop, fbtoc, f, ft, feet, fbgs, ftbref