This graphs are the results of a matlab script that calculate shoaling and channel infilling. Its algorithms allow me to account for depth, width, water flow, course sediment load (bigger particles, like sand, usually moving along the bottom of the water channel as bed load) and fine sediment load (finer particles like clay, usually suspended in the water column) and approximate change in deposition and bypass over time.
It’s an exciting tool, and I couldn’t have used it without the help of Dr. Julie Rosati and Kenneth Mitchell of the US Army Corps of Engineers. For my purposes I do understand it to have limitations- it accounts for the shape of the channel in section, but not very well in plan. For instance, the helical currents that exists in a curvy channel (like the Riachuelo) create areas of faster and slower flow in plan which causes sediment to pile up on the inside curve and while the channel on the outside curve stays clear.
This tool will allow me to establish a periodicity to the dredging cycle- in short, when the green line gets above the percent (the decimal on the y axis) that the channel is allowed to infill and still stay open for navigation, then the sediment must be cleared. Here, I am showing on the left a calculation estimating infilling rates for a depth of 20 feet (the approximate current depth, though in reality it varies wildly due to lack of maintenance) and on the right the infilling rate for a depth of 10 feet- the new design depth for the central channel. This tool allows me to understand how much sediment needs to be moved how often, but in a non-spatial way.
To work beyond the limitations of this tool I intend to build an analog channel-shape model that will enable me to spatialize these results and test the effects of formal design moves on the deposition locations. I hope I can then feed this information (measuring proportions of sediment from different locations) back into the matlab model in a much more localized and specific way, running myriad tests that help me account for specific approximations of sediment deposition as part of a larger landscape strategy for the Riachuelo Canal.
Expect to see many more of these graphs…