Irrespective of their spatial extent, free-surface shallow flows are challenging measurement environments for most instruments due to the relatively small depths and velocities typically associated with these flows. A promising candidate for enabling measurements in such conditions is Large-scale Particle Image Velocimetry (LSPIV).
Muste, M., A. Hauet, I. Fujita, C. Legout, and H.-C. Ho. “Capabilities of Large-Scale Particle Image Velocimetry to Characterize Shallow Free-Surface Flows,” Advances in Water Resources, 70(2014), pp. 160–171, 2014.