Preliminary Dye & Drifter Releases: Where did it go and how far could it be observed?

As the WHOI guys were deploying the AWACS, we did a preliminary investigation of dye and drifter releases.    We were curious to see where it would go and how far dye could be visually tracked from a boat.    The model simulations made it look like dye and drifters would just JET a few kilometers offshore on the main channel.

We went out at about 10:45, just as the tide was starting to ebb.  We admired the WHOI folks deploying their AWACS in their wimpy (yet fast) boat.    For sure, Whit was the saltiest dog on that vessel!

We released 3 drifters and Guza poured a gallon of 23% Rhodamine off the side of the boat at about x=-800 m and y=-100 m in the RIVET coordinate system (see photo below). For reference see the bathymetery map that Jesse made in an earlier post.

Above is what the dye looked like a few minutes after released from the boat.  The dye was advected fairly rapidly near the shoreline and spread longitudinally.   Eventually it hit the opening of the inlet.   The photo below shows the dye patch as it hits the inlet mouth. This location is about x=0 m and y=-300 m in RIVET coordinates.   It is the view in the roughly +y direction from the rental house

Later (photo below), the dye moves both along the beach to the south and offshore, but over the shoal – not in the channel.

This can be more clearly seen a little while later in the photos below.

The photo below shows the view later on (15-20 minutes after the first photo above) more towards the south (in +x  and slightly in the -y direction).   A blob (fraction) of the dye is clearly moving alongshore down the beach – as other parts of the patch spread out over the entire ebb shoal.

In the end the dye broadly spread out over the entire shoal to the south.  The 3 drifters that we released also crossed over the southern ebb shoal and went offshore eventually into 4 m depth where we picked them up.     No dye was observed to go out of the newly dredged main channel.   This may have been because we released at the start of ebb as the tide was still relatively high.   The map below highlights in slightly transparent pink the approximate visual extent of the dye patch about 30-45 minutes after the dye was released.

At extremely low tide, the ebb tidal velocity is still very strong and it is now visually clear that likely very little transport is occuring over the southern ebb shoal.   It is in ankle to knee depth water.    So perhaps inlet tracer transport and fate depends a lot on the tidal stage.    This will be fun.

 

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