Knowledge of the flow patterns within distributary systems is key for understanding deltaic hydro- and morpho-dynamics, yet synoptic measurements of flow fields remain virtually nonexistent. As a means of overcoming this problem, a small number of studies have used biogenic surface films as synoptic flow tracers, under the assumption that biofilm streaklines are tangent to the local flow direction. Here we rigorously test this assumption and show that, despite flow patterns that change severely in space and time (over a range >270°), streaklines are relatively accurate synoptic flow tracers for the Wax Lake Delta, in Louisiana. When the incoming discharge was greater than 2400 m3
/s with stable or falling tides, the streakline-derived flow direction departed from near bed flow direction measurements of 22.8° (root mean square). When the discharge was greater than 2400 m3
/s and the tides were rising greater than 0.03 m/hr, they were accurate within 28.0°. Under conditions of discharge less than 2400 m3
/s and tidal change less than a positive 0.03 m/hr, they were accurate within 33.3°, while during low discharge and rising tides they were accurate within 58.9°. Accuracy varied with distance from the delta, with proximal sites having greater precision. Our results demonstrate that a streakline-derived flow direction can characterize the spatiotemporal variability in the flow directions, but that the accuracy is significantly influenced by the hydrodynamic conditions and location within the network.
This is an open access article distributed under the Creative Commons Attribution License
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited