Estimating Gravel Particle Sizes Based On Field Photographs Using The Rock Observation Calculator (roc)

The Rock Observation Calculator (ROC) is a software program developed by the United States Army Corps of Engineers (USACE) Engineering Research and Development Center (ERDC). This tool aims to provide an estimate of the gradation of sediment samples based on field photographs. Taking many sediment samples in the field can be a cumbersome process, depending on the number of samples obtained and the location of the samples. The ROC tool provides a more efficient means of obtaining sample gradations without requiring intensive sample collection and analysis. To test this tool, samples were obtained from gravel bars on the Big Blue River near Marysville, KS. A photograph was taken of the sample in a 1 meter by 1 meter square, after which a pebble count was conducted to determine the actual gradation of the sample. All three axes were measured to most accurately estimate the volume of the grains. The ROC tool uses local thresholding to segment the pixels into distinct particle identification. ROC then uses the identified particles to estimate a gradation by mass and by volume. Due to the limitations of the segmentation process, the tool performs optimally when the gradation is fairly uniform and performs less optimally when the difference between small and large particles increases. This analysis assesses the merits and limitations of using the ROC tool on a gravel bar.