Automated Salt Dilution Instream Q (ASDIQ) with Image Velocimetry (IV): It Looks Like a Salty Marriage

Salt Dilution (SD) is an accurate, safe, relatively inexpensive and easily employed method to measure water flow in turbulent streams and rivers.  It has been used in some form for over 100 years and continues to experience a renaissance with refined methods and improved technologies.  However.. SD is challenging in less turbulent flows without “complete” lateral mixing, and also requires a continuous estimate of water level or other proxy to generate a continuous hydrograph. Image Velocimetry (IV, Large Particle IV or Space Time IV), on the other hand, has been used for more than 20 years to estimate the flow in more placid rivers and streams without making contact with the water, using high resolution video to measure the surface velocity.  However.. apriori estimates of the surface (V_S) to bulk (V_B) velocity ratio (k) is required, as well as the channel wetted area (A).

In this research we examine whether we can marry the two technologies to create a comprehensive automated flow measurement system to span all flow regimes from turbulent to placid, by removing the need for apriori knowledge in the case of IV, and using continuous imagery as the proxy flow estimate in the case of SD.  SD measures Q; IV measures V_S; this method combines the two using the equation Q = V_S*k*A to estimate continuous Q, as well as an estimate of surface to bulk velocity ratio (k), and wetted area (A).

The method/system has the potential to replace conventional stations that rely on expensive and dangerous site visits and error prone water level sensor proxies.  The results of our preliminary investigations are presented for 3 test stations.