The focus of a study led by an international team including Ph.D. student Brandee Carlson from Rice University was sediment delivery of abandoned distributary channels and surface water connections. River diversions in the Huang He cause channels that line the coast of the sea to transition to tidal mud flats. The sediment input from tides accumulates in these abandoned channels. Carlson and her team have used tilt current meters (TCM-1 and TCM-4) since 2016 to look at how sediment accumulation affects delta dynamics. TCM’s were deployed along the delta bed by placing them on the mud flats tethered to concrete blocks. The devices will determine the bottom speed and direction to help understand sediment movement through the river and along the delta.
The TCM’s were effective in the delta, Carlson said, “because you could place them a few meters deep in mud flats at intertidal elevations that get inundated with only half a meter of water in fair weather”. It was co-located with an acoustic meter to do comparison data. “They are really easy to work with and compared to the cost of acoustic meters you basically have an instrument which can get the time series you need with more points at the field site which is really important for this study. It was instrumental in looking at ... [changes] over space and time.”
The TCM’s held up considerably in a sediment laden environment where there is potential for the devices to become buried. In the summers they were deployed for 6-week intervals and in the winter for 2 weeks. With tidal flats changing all the time, the data was “faithfully recorded”, according to Carlson. “The advantage of these meters is that you can be bolder with the instrument placement.”
The research will help to understand how abandoned deltaic distributary channels fill with sediment and how they evolve. On a broader scale, it will help to see how channels from diversions, both natural and engineered, compare and also look at the seasonal component of sediment transport. In addition, the study will help to build predictive models for coastline stability.