Tuesday, April 10, 2012

Flow, velocity and tidal harmonics in a restored coastal marsh

By François Birgand and Randall Etheridge


The goal of this post is to provide some fascinating flow patterns we have observed in a restored marsh where we evaluate the ability to dissipate excess nutrients coming from adjacent agricultural lands.  You may find our latest results here presented at the NC WRRI conference in March 2012.  You may also visit the site dedicated to the marsh results.

In the video below, you will see the flow and velocity patterns observed in November 2011 at the upstream station.  The tidal fluctuations are represented in the middle by rising and falling rectangles.  Flow is represented on the left.  Positive flow represents ebbing tide (water penetrates in the marsh coming from upstream agricultural land) and negative flow, flowing tide.  You may observe that there are no two same tides and tidal cycles.  Water quality parameters and concentrations also vary dramatically.  Another blog will be published on that subject.

It is particularly interesting to see a very peculiar pattern at high tide where flow can suddenly be inverted, which induce 8 shape curves.  This is due to the existence of a flow loop in the marsh.


video



At the downstream station, the tidal harmonics exhibit a more expected behavior.  Watch for the differences in the flow and velocity scales.

video


This needs to be accompanied by the water quality analyses, but we thought we should post this now for your enjoyment!

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