Simplified conversions between specific conductance and salinity units for use with data from monitoring stations

The U.S. Geological Survey, Bureau of Reclamation, and the California Department of Water Resources maintain a large number of monitoring stations that record specific conductance, often referred to as “electrical conductivity,” in San Francisco Bay Estuary and the Sacramento-San Joaquin Delta. Specific conductance units that have been normalized to a standard temperature are useful in fresh waters, but conversion to salinity units has some considerable advantages in brackish waters of the estuary and Delta. For example, salinity is linearly related to the mixing ratio of freshwater and seawater, which is not the case for specific conductance, even when values are normalized to a standard temperature. The Practical Salinity Scale 1978 is based on specific conductance, temperature, and pressure measurements of seawater and freshwater mixtures (Lewis 1980 and references therein). Equations and data that define the scale make possible conversions between specific conductance and salinity values.

This article presents a simplified conversion to salinity units for use with specific conductance data from monitoring stations that have been normalized to a standard temperature of 25 °C and an equation for the reverse calculation. Although these previously undocumented methods have been shared with many IEP agencies over the last two decades, the sources of the equations and data are identified here so that the original literature can be accessed.