Uncertainty estimation for salt dilution gauging for streamflow measurements

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Accurate information about how much water flows through our rivers is essential for planning of hydropowerproduction, drinking water supply, flood management, and ensuring a sound habitat for Salmonids and otherfish. In steep mountain streams, many of the techniques that are used to determine the streamflow are not easyto perform. One of the techniques that does give a good estimate of the streamflow is salt dilution gauging. Inthis technique, a known small quantity of ordinary kitchen salt is added to the river. A few hundred metersdownstream, it is then measured how salty the water is, by measuring how easily it conducts electricity. Theless salty the water is, the more water was flowing through the stream diluting the salt. With some calculationsthe quantity of water flowing through the stream can be determined quite accurately.How accurately the estimates are is currently a source of debate. Since important decisions depend on it, wewant to know how accurate this method is in various circumstances (for example flood flows or low flowsduring a dry summer), and how the accuracy depends on the quantity of salt added.In this research we will develop better methods to put a number on the accuracy of the measurements, so thatdata collected in many small streams can be confidently added to the database of information about ourstreams. This benefits many sectors and allows us to keep a sharp eye on one of our most precious naturalresources.