SFM SEDIMENT FLUX ESTIMATION ON A TIDAL DELTA NEAR MBWENI, TANZANIA

We mapped a tidal delta near Mbweni, Tanzania, over two successive tidal cycles in order to estimate the rate, direction, and style of sediment transport using structure from motion (SfM). We combined mapping results with observations of sedimentary structures on the delta to help determine the relative contributions of fluvial, tidal, and wave inputs to sediment flux.

The delta we studied is spatially small (~500 m along shore, and ~500 m cross shore), and during the time we visited (late June, 2017) had moderate stream flow (rainy season had just ended), high tidal cycle (~3 m tidal range), and moderate wave climate (no storms were present). Delta morphology suggests that wave action dominates sediment transport on the delta, but our measurements suggest that at least during times of high tidal range tidal sediment transport may overwhelm wave action.

Google Earth imagery taken a year after our measurements (August 2018) suggest that the Mbweni delta is, on longer timescales, dominated by wave action, with further straightening of the shoreline and delta front. SfM observations can be taken relatively quickly, and allow considerably more resolution on the timing and mechanism of sediment transport than would be available using morphology alone. We suggest that such studies will make it possible to quantify when and how sediment is moving within a sedimentary system.