Gravity-driven currents play a significant role in many natural and anthropogenic fluid processes such as deep ocean sediment transport, pyroclastic flows, river plumes and industrial buoyant jet discharges. They hold certain ecohydraulic interactions of interest, such as their behaviour along biodiverse submarine canyon beds and their interaction with flora in littoral zones of aquatic environments. Over the last three decades, studies have reproduced gravity currents in the laboratory to provide insights into their characteristics. This has helped to develop and validate theoretical models, which are sought after to numerically recreate large-scale occurrences.

Photometric techniques for characteristic flow measurement of experimental gravity currents have developed over the last two decades. They are non-intrusive on flow, can provide simple velocity measurements of current boundaries and capture visual characteristics. They are also comparatively cheap to other techniques. However, photometric techniques at present are limited in their use to opaque, sediment-laden currents. They have not been explored for in-depth quantitative measurement of flow structures, which would provide important information about current development and interaction with obstacles. In the following study, sediment-laden currents are released in a lock-exchange flume at varying densities and over a range of different substrates. A rectangular obstacle is placed across the width of the flume. High spatio-temporal resolution images of the current are used to develop a novel, quantitative measurement technique for structures within gravity current heads. The technique benefits experimental work where intrusive measurement techniques may not be feasible, and can be useful to study ecohydraulic interactions.