Measurements of discharge by conductivity method

Abstract

Electrical conductivity is a useful technique for determining discharge for engage stream profilestr. It is based on a simple relationship between discharge, conductivity and total dissolved solids concentration. The electrical conductivity of a water is mostly proportional to its total dissolved solid content. If repeated at the same place for a range of river depths, it can be used to build up a depth-discharge rating curve. In first step, make a primary solution by dissolving salt (NaCl) in river water; 150 g NaCl in 1 l of river water is required for each 100 1 s^-1. Inject the solution into the stream at once. Measure conductivity and time at the downstream until the peak produced by the passage of the salt has passed and the conductivity has returned to its original level. Make up a secondary solution adding a small volume of primary solution to the large volume of stream water. Relative concentration of this solution can be calculate! according to Eq.2. Place a relatively large amount of river water in clean container and add secondary solution in small increments, stir thoroughly and measure the conductivity until the highest conductivity observed in the stream is obtained. Calculate relative concentration according tp Eq.3 and convert the conductivity readings in the stream to relative concentrations. Calculate discharge by the Eq.3.