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…how to safely and accurately measure flood flows, turbulent flows in steep boulder fields, and flows over a wide range quickly.   There is an effective way: it’s called Salt Dilution (ISO9555).  Salt-dilution discharge measurement is a method in which a known mass of salt [NaCl] is injected upstream of a turbulent reach and the downstream conductivity signal measured.   But how do we validate the flow measurement?  How do we collect flows at a target level? How do we build a rating curve quickly and cost effectively?  That is why we started Fathom.

If you are new to the Salt Dilution method, the Laberge document is a comprehensive review of the method, especially for winter low flows, along with an ecological impact study in Appendix D.  The Streamline article by Hudson and Fraser provides a good overview of the method, but lacks current best practices.  This Sounding post is a revision of that article to represent current best practices.  Dan Moore’s Streamline article presents a slight variation to Hudson and Fraser.  The most recent Confluence article we wrote on the Temperature-compensated Concentration Factor contains a comprehensive list of reference articles.  The method has been used for at least 5 decades now (Østrem, G. 1964) and proven to be very accurate in turbulent streams and rivers.  The BC British Columbia Resource Inventory Standards Committee (RISC) best practices guidelines on the method is published here.

We have developed an online tool to process and manage your Salt Dilution measurements, either QiQuac or AutoSalt.  It also features compound hydraulically-based rating curve development tools. The WIT-HM tool is in beta now.  Ask us to be a beta tester.