Embodiments relate to characterizing a water flow. Initially, a camera targeted at the water flow obtains images. An image pyramid is generated for each image, and a first level of each image pyramid is tiled at an initial scale to identify initial features. The initial features are matched across the first level of the image pyramids at a pixel-level to obtain a first set of feature displacements. A second level of each image pyramid is tiled at a decreased scale to identify a scaled set of features. The scaled features are matched across the second level of the image pyramids at the pixel-level to obtain a second set of feature displacements. Optical flow algorithms are applied to modify each feature displacement to account for a corresponding subpixel registration. A stereo reconstruction is applied to the feature displacements to generate a three dimensional (3D) displacement map.