A two-color optical method for determining layer thickness in two interacting buoyant plumes

We describe a technique for measuring the layer thickness of two interacting buoyant rotating gravity currents. The technique can be used generally to differentiate between water masses in experiments with multiple sources and is used here to simulate the dynamics of two adjacent coastal river plumes. The plumes are generated using two identical fresh water inlets, with blue and red dye indicating upstream and downstream river flows, respectively. Two parameters, normalized intensity and color ratio, are measured with a 3-CCD color video camera and used to develop a two-dimensional (intensity–color ratio) calibration map for layer thickness. The calibration is used successfully to determine the depth field for the combined two-plume system and to differentiate between the two plumes. This technique is applied to compute the volumetric growth of a large eddy near the freshwater source and the transport rate of buoyant fluid away from the source in the coastal current. The validation tests show good agreement between the calculated plume volume and the input fresh water volume.