Re-directed from the "stills from the ROV" thread
Not sure if this is the best place for this question but it is relevant to the ROV search. Has any attempt been made to model the flow of water over and down the the reef? In particular I am thinking about the outflow from the lagoon after storms or high tides. The "landing strip" area is not far from the main channel and that flow should move materials on the upper reef during periods of drainage. I think the NC shelters the "landing strip" somewhat from the channel but it still may influence the distribution of debris down the reef face and may need to be taken into account in terms of the area to be searched.
Matt
Here is my impression. See photos below. Under normal tidal situation, the flow into the lagoon, highlighted as Green, comes through the Tatiaman passage and into the lagoon. A lot of the flow goes straight in, and then makes the right hand turn as it rebounds of the far shoe of the lagoon, which is why Taria point, that promontory that sticks into the lagoon from the far side, is there.
The normal outflow, highlighted as Blue, draws from all of the lagoon towards the passage, and disperses it seaward of the channel in all directions "north and south" along the reef flat. Since the ocean level is lower than the lagoon level, the water simply goes downhill wherever it can toward the ocean. The current can be pretty good right in the channel, but once it spreads out it isn't quite so strong. You can still walk around on the reef flat during an outflowing tide, so it isn't like it will sweep you off your feet. Also note that the water coming out of the lagoon is nearly 10° warmer than the surrounding ocean, so once it gets to the ocean, it is going to float on top of the colder ocean water rather than cascade down the reef face as you might imagine.
I don't see normal tidal flow as much of an agent of change with regards to moving big pieces of stuff around. That would more likely be reserved for waves and storm events.
Most storms evidently come with wind, and therefore waves, out of the NW. This "packs" water into the lagoon through the Tatiaman passage regardless of tidal condition. Enough packing, and the bowl overflows so to speak, spilling out both Baureke Passage, and also we believe down by the end of the lagoon where the CG station was - see the red lines.
You can clearly see that Baureke passage is open to flow in this 2007 sat photo, but it was high and dry in 2001, only marginally open in 2010, and evidently high and dry again in a sat photo taken most recently on 6/16/12, so it would seem that Baureke passage only once in a while serves a a relief valve for the lagoon. Note the vegetation pattern around Baureke that has some areas devoid of bush, this I think is evidence of the occasional over wash in this area, leaving a scar on the landscape, if you will.
After a storm, all that water left in the lagoon would again flow out the main channel, perhaps in a stronger flow than normal, but generally in an orderly fashion, so to speak, downhill in all directions towards the ocean. Again, I don't see this being an agent of change when it comes to moving big stuff around.
What moves big heavy stuff around on the reef are the waves and particularly storm related surf. Large amounts of water with major momentum is where the energy is to be found, and it generally pushes stuff shoreward and southward along the western shoreline rather than dragging it out to sea. See the second photo attached which shows the large blocks of coral, some as large as bulldozers, thrown up on the reef flat. You can also see the area from which they came, the broken edge of the reef with the rectilinear lines vs the softer surf lines. Note that the tide in this second photo is really low which is the only time that broken edge of the reef is above water. We've seen it at extreme low tides where the water from the reef flat is cascading over this edge in a little waterfall into the ocean.
None of this probably answers your question. I don't think we've modeled it beyond my description above as I don't think it was tidal outflow from the lagoon or a storm event that moved the Electra in our scenario. I prefer to see the rising tide on the ocean side, combined with waves, eventually floating the aircraft, either largely intact or in big pieces - definitely buoyant in comparison to NC debris or coral blocks - to the edge of the reef and beyond. After that, water infiltration, ocean current, "aquadynamics" (does an aircraft fly underwater?), and gravity do the rest.
The current off the edge of the reef generally heads to the NW along both sides of the island - see the Yellow lines, so if I were directing the deep water search I'd start N of the NC wreck, and work N to NW on the assumption that the aircraft, or big parts thereof, were floated off the reef by wave action and carried in that direction before hitting the bottom.
How long or far before hitting the bottom is another question, and you can find lots of threads in the Forum asking how long the Electra would float, whether or not it would be relatively intact or in pieces, etc. My personal thought is that it got floated off the reef mostly intact, perhaps without the landing gear and some of the skin, maybe some bigger parts torn off as indicated by the dado's coming ashore. Ric I think is more on the side of the aircraft getting beat up pretty badly in the surf and therefore not floating away particularly far.
I hope that helps.
Andrew