Introduction to Salt Dilution Gauging for Streamflow Measurement Part IV: The Mass Balance (or Dry Injection) Method

In part one of this series, Moore (2004a) introduced the general principles of stream gauging by salt dilution. In subsequent articles, Moore (2004b, 2005) described techniques of constant-rate injection and slug injection using salt in solution. This is the final article in the series and details the “mass balance method.” Originally described by Elder et al. (1990), the mass balance method differs from slug injection using salt in solution (Moore 2005) in that it is based on conservation of tracer mass, not of tracer volume. By using the mass balance method, salt can be injected into the stream either in dry form or in solution. Because it is more common to work with dry salt, this method has also become known as the “dry injection method.”