Going against the flow
June 28, 2011 11:50 PM Subscribe
Can a dead body somehow float upstream in a river?
In a boating accident in a river, a small boat carrying three people capsized. The accident happened even as they were in sight of some people on the shore and in another boat. While one person from their boat was rescued by these onlookers, the other two appeared to have drowned. A few days later one body was found about 2 kilometres downriver of the accident site. A couple of days later, another body was found 5 kilometres upriver of the accident site. It has been confirmed that the bodies were of the two missing people. There doesn't seem to be any possibility of any animal dragging one of the bodies upstream.
What could be a scientific explanation for this? Do rivers have some kind of counter-currents at the edges or near the bottom?
Note 1: I am giving the details as reported in the media. It is, of course, entirely possible that someone has messed up the reporting, as all reports seem to be rephrasing the same material.
Note 2: I am not linking to the news reports pertaining to this accident. I hope it is possible to discuss/answer this without going into the specifics of this particular accident. I don't like the idea of a relative of any of those unfortunate people stumbling over this AskMe.
In a boating accident in a river, a small boat carrying three people capsized. The accident happened even as they were in sight of some people on the shore and in another boat. While one person from their boat was rescued by these onlookers, the other two appeared to have drowned. A few days later one body was found about 2 kilometres downriver of the accident site. A couple of days later, another body was found 5 kilometres upriver of the accident site. It has been confirmed that the bodies were of the two missing people. There doesn't seem to be any possibility of any animal dragging one of the bodies upstream.
What could be a scientific explanation for this? Do rivers have some kind of counter-currents at the edges or near the bottom?
Note 1: I am giving the details as reported in the media. It is, of course, entirely possible that someone has messed up the reporting, as all reports seem to be rephrasing the same material.
Note 2: I am not linking to the news reports pertaining to this accident. I hope it is possible to discuss/answer this without going into the specifics of this particular accident. I don't like the idea of a relative of any of those unfortunate people stumbling over this AskMe.
Best answer: Some rivers are tidal and that may move the body somewhat. Alternatively, it may have caught on a boat or other watercraft and been dragged upstream without anyone noticing.
posted by ninazer0 at 12:06 AM on June 29, 2011 [6 favorites]
posted by ninazer0 at 12:06 AM on June 29, 2011 [6 favorites]
Response by poster: Additional info:
The incident happened at a point in the river that is several kilometres away from the point where the river enters the sea. My guesstimate (looking at Google maps) is 25-35 km. The river takes a very winding route, but the tides may be a factor. The incident site itself is unlikely to be misreported as it is a tourist spot.
Also, I doubt if there were multiple reporters covering this. It wasn't a major news item. All reports read like very minor tweaks of the same basic, bare facts. And I forgot to mention that the same numbers are reported in the official press releases by the local police department that ran the search and rescue operation. So, if someone has messed the numbers up, it is probably just one careless person.
posted by vidur at 12:20 AM on June 29, 2011
The incident happened at a point in the river that is several kilometres away from the point where the river enters the sea. My guesstimate (looking at Google maps) is 25-35 km. The river takes a very winding route, but the tides may be a factor. The incident site itself is unlikely to be misreported as it is a tourist spot.
Also, I doubt if there were multiple reporters covering this. It wasn't a major news item. All reports read like very minor tweaks of the same basic, bare facts. And I forgot to mention that the same numbers are reported in the official press releases by the local police department that ran the search and rescue operation. So, if someone has messed the numbers up, it is probably just one careless person.
posted by vidur at 12:20 AM on June 29, 2011
Best answer: I thinks tides are most likely explanation. You said "the river takes a very winding route." This suggests a flat coastal plain, so the river could be tidal a long ways inland.
posted by nangar at 12:47 AM on June 29, 2011 [3 favorites]
posted by nangar at 12:47 AM on June 29, 2011 [3 favorites]
I'm not qualified to comment on whether this is a feasible river occurrence. However, I have seen blatantly incorrect information funneled through county sheriff press offices (unintentional errors, but clearly and factually incorrect nonetheless, and unfortunately the media often just parrots the error). These mistakes do happen.
posted by samthemander at 1:18 AM on June 29, 2011 [2 favorites]
posted by samthemander at 1:18 AM on June 29, 2011 [2 favorites]
Best answer: Our local river system is tidal. It's also popular for suicides and drunken accidents. Bodies are recovered both up and downstream from point of entry. It's quite typical for a body to float downstream at high tide, get caught, and turn up upriver weeks later when it is freed and carried by the inbound tide. Here is an example; Tivoli is upriver of the city centre where the student drowned.
posted by DarlingBri at 3:51 AM on June 29, 2011
posted by DarlingBri at 3:51 AM on June 29, 2011
Depending on the size of the river, it could have been pushed upstream by a boat. There wouldn't necessarily be damage to the body if it were slowly pushed along by a slow-moving tourist barge, say. Although 5km seems pretty far for nobody to have noticed it.
posted by DU at 4:57 AM on June 29, 2011 [1 favorite]
posted by DU at 4:57 AM on June 29, 2011 [1 favorite]
I too think the most likely explanation is either the tide or the reporting. There are portions of rivers that flow upstream: eddies. Essentially what happens is that as water flows around an obstruction in the river (even an unseen obstruction), it must flow back upstream to fill in behind the obstruction. There are many types of eddies, and some, behind large obstructions that displace a large amount of water, can be quite big. However, they aren't kilometers big, more like hundreds of yards big.
posted by OmieWise at 4:58 AM on June 29, 2011
posted by OmieWise at 4:58 AM on June 29, 2011
Best answer: There's a lot we don't know here. For example, without knowing the cfs (cubic feet per second, the rate of flow), the width, depth, etc. I know some places are already in high-summer, which means less available water. I know our river here, the Mighty Monongahela, was up until about 5 days ago literally moving 0 water through lock systems because of a lack of rain. It stayed like that for 2-3 weeks.
Even with flow, there are always back currents that move differently than you might suspect, especially around bends and curves, and especially as depths change. I suspect your tides may be to blame here, especially depending on your watershed. Where I lived in Florida (strange, because it only gets 1 tide per day), you can time your kayak trips so that you're not actually paddling either direction, just surfing the current.
I used to do some SAR work, and we trained a lot on local whitewater waters. Even in fast flows (think like 5k cfs in a body of water 50 feet wide) it's not uncommon for bodies to wind up in completely different orientation than you might expect. Hydraulics, the rate of decay of the body, changing flows---all matter and all move the body around.
5km seems significant, but not really for ~5 days, especially because dead bodies w/o PDF's are often somewhat neutrally buoyant and will float on the thermocline under the water...right up until they bloat enough to float. Sorry if that's too graphic.
posted by TomMelee at 5:26 AM on June 29, 2011
Even with flow, there are always back currents that move differently than you might suspect, especially around bends and curves, and especially as depths change. I suspect your tides may be to blame here, especially depending on your watershed. Where I lived in Florida (strange, because it only gets 1 tide per day), you can time your kayak trips so that you're not actually paddling either direction, just surfing the current.
I used to do some SAR work, and we trained a lot on local whitewater waters. Even in fast flows (think like 5k cfs in a body of water 50 feet wide) it's not uncommon for bodies to wind up in completely different orientation than you might expect. Hydraulics, the rate of decay of the body, changing flows---all matter and all move the body around.
5km seems significant, but not really for ~5 days, especially because dead bodies w/o PDF's are often somewhat neutrally buoyant and will float on the thermocline under the water...right up until they bloat enough to float. Sorry if that's too graphic.
posted by TomMelee at 5:26 AM on June 29, 2011
Was the body tethered to a salmon making its way upriver to spawn? If not, I would assume tidal action or good old human error.
posted by baggers at 6:15 AM on June 29, 2011 [1 favorite]
posted by baggers at 6:15 AM on June 29, 2011 [1 favorite]
Best answer: Tidal effect seems like a strong possibility. Also, depending on the buoyancy of the two bodies, wind might drive one upstream while not affecting the other at all.
This is one of those complex situations where there is the answer they want on a highschool physics test (multiply the flow of the river times the time until they find the body) is not even good as a rough aproximation of what will really happen.
posted by Kid Charlemagne at 6:33 AM on June 29, 2011
This is one of those complex situations where there is the answer they want on a highschool physics test (multiply the flow of the river times the time until they find the body) is not even good as a rough aproximation of what will really happen.
posted by Kid Charlemagne at 6:33 AM on June 29, 2011
Best answer: Tidal flow is probably your best explanation for this (assuming someone/thing didn't relocate the body).
Wind advection is usually not strong enough to move an object which lies low in the water (like a body) against a current. Typically, the object will move at the speed of the local water current (coupling to water flow is total) and only at 10% or less of the wind speed. Thus, the wind needs to be ten or thirty times more than the 1-2 knots of most rivers to push against the current. That's a very heavy storm.
While there are natural eddies in rivers, they usually lead to debris catch points, where the body would beach. Also, as others say, they tend to be much shorter range than 25 km. I've never seen one more than a few hundred meters.
Depending on the river, 25-35 km inland is a believable range for tidal flow. Tides affect the St. Lawrence for hundreds of km.
posted by bonehead at 6:36 AM on June 29, 2011
Wind advection is usually not strong enough to move an object which lies low in the water (like a body) against a current. Typically, the object will move at the speed of the local water current (coupling to water flow is total) and only at 10% or less of the wind speed. Thus, the wind needs to be ten or thirty times more than the 1-2 knots of most rivers to push against the current. That's a very heavy storm.
While there are natural eddies in rivers, they usually lead to debris catch points, where the body would beach. Also, as others say, they tend to be much shorter range than 25 km. I've never seen one more than a few hundred meters.
Depending on the river, 25-35 km inland is a believable range for tidal flow. Tides affect the St. Lawrence for hundreds of km.
posted by bonehead at 6:36 AM on June 29, 2011
Best answer: Dead bodies float, especially after some time has passed. The upriver body was found last, I note. Still, that's a very long way to be blown by winds. Can you find out if the river is tidal? I think that's the best theory.
posted by CunningLinguist at 6:49 AM on June 29, 2011
posted by CunningLinguist at 6:49 AM on June 29, 2011
I don't really get how animals can be disregarded. When I first read it, I assumed it meant there were no claw/teeth marks. But if the body were clothed, there wouldn't necessarily have to be. There could be puncture marks in the clothing that subsequently ripped off.
Even nude, actually, since a river dolphin could push it along, for instance. Or crocodile/hippo/etc.
posted by DU at 7:43 AM on June 29, 2011
Even nude, actually, since a river dolphin could push it along, for instance. Or crocodile/hippo/etc.
posted by DU at 7:43 AM on June 29, 2011
Best answer: dead bodies w/o PDF's are often somewhat neutrally buoyant and will float on the thermocline under the water.
A picnocline (salt/fresh layer) could do the same thing too, especially in an esturarine river. Depending on the river slope, 25 to 30km inland may still be brakish.
posted by bonehead at 8:08 AM on June 29, 2011
A picnocline (salt/fresh layer) could do the same thing too, especially in an esturarine river. Depending on the river slope, 25 to 30km inland may still be brakish.
posted by bonehead at 8:08 AM on June 29, 2011
As far as tidal influence goes--the Hudson River is considered a tidal estuary all the way up to the Tappan Zee Bridge, at least 50 km north of lower New York, where it starts to open up into the ocean. This means a significant amount of salt water is flowing upland this far, enough to support salt-water animals like clams, oysters, crabs etc. Beyond this point, the Hudson is still tidally influenced (meaning that the flow of the river is affected to some degree by tides) all the way up to Albany, another 200+ km. So, I wouldn't discount tides as a potential cause of upstream movement in your case.
posted by Jemstar at 8:09 AM on June 29, 2011
posted by Jemstar at 8:09 AM on June 29, 2011
Best answer: Part of my work deals with using stationary sonar. I have never been involved directly in a body search but a coworker has done several successful recoveries, and I have taken classes from a guy who probably has more experience with body search and recovery than anybody else. Some of the following may be disturbing.
First of all, I can say that rivers can definitely have more than one current direction and density composition. I have worked in the Mississippi River and have definite proof that although the surface current in the area I was working had an extreme downstream current, the water was calm at the 30-40' depth and then flowed upstream at the bottom half. This was on a straight section between two bends. An instrument lowered on a cable went downstream on the surface at a 45 degree angle, then turned and was actually 5-10' upstream of the deployment point on the bottom. This effect could be tidal, from density changes from ocean or other river intrusion, or simply from depth changes in the river.
Most people think the average body is neutrally buoyant, and its usually pretty close, but this assumes there is air in the lungs. When an accident like this occurs, or even is someone just falls overboard, most of the air is knocked out of their lungs. If they are conscience they often gasp for breath, even when underwater, and their lungs fill with water. When unconscious they may stay collapsed. In any case, they become negatively buoyant and sink. Even when there is a strong surface current the body almost always settles less than the water depth away from the point of entry, and often do not move for a day or two.
As gasses build up in the body cavities during decomposition, the body becomes positively buoyant and will float again, sometimes even when weighted down. At some point in this process they become neutral and this is when underwater travel occurs. It is possible the body could be dragged by a biologic, but more likely followed the current at the density point in the river where they were neutral. This could be why one was found downstream and the other up, they were just different densities and floated at different depths or times.
If there is barge or large boat traffic in the river the body could be pulled along without even touching it like a large truck will pull your car on the highway. If the body was dragged by an animal or boat there should be pretty clear signs.
posted by Yorrick at 8:36 AM on June 29, 2011 [4 favorites]
First of all, I can say that rivers can definitely have more than one current direction and density composition. I have worked in the Mississippi River and have definite proof that although the surface current in the area I was working had an extreme downstream current, the water was calm at the 30-40' depth and then flowed upstream at the bottom half. This was on a straight section between two bends. An instrument lowered on a cable went downstream on the surface at a 45 degree angle, then turned and was actually 5-10' upstream of the deployment point on the bottom. This effect could be tidal, from density changes from ocean or other river intrusion, or simply from depth changes in the river.
Most people think the average body is neutrally buoyant, and its usually pretty close, but this assumes there is air in the lungs. When an accident like this occurs, or even is someone just falls overboard, most of the air is knocked out of their lungs. If they are conscience they often gasp for breath, even when underwater, and their lungs fill with water. When unconscious they may stay collapsed. In any case, they become negatively buoyant and sink. Even when there is a strong surface current the body almost always settles less than the water depth away from the point of entry, and often do not move for a day or two.
As gasses build up in the body cavities during decomposition, the body becomes positively buoyant and will float again, sometimes even when weighted down. At some point in this process they become neutral and this is when underwater travel occurs. It is possible the body could be dragged by a biologic, but more likely followed the current at the density point in the river where they were neutral. This could be why one was found downstream and the other up, they were just different densities and floated at different depths or times.
If there is barge or large boat traffic in the river the body could be pulled along without even touching it like a large truck will pull your car on the highway. If the body was dragged by an animal or boat there should be pretty clear signs.
posted by Yorrick at 8:36 AM on June 29, 2011 [4 favorites]
Response by poster: Thanks all. The river is definitely tidal. I have checked the relevant official websites and they mention that tidal effects are felt in that river some 30 more kilometers upstream than the accident spot. I couldn't find a depth profile of the river, so I am not sure how deep it is at various places. But it is certainly has large boats, ferries, barges etc. going up, down and across.
So, I think the tides coupled with different densities of water at different depths, plus perhaps the drag of some barges, explain it as best as is possible under the circumstances.
posted by vidur at 2:52 PM on June 29, 2011
So, I think the tides coupled with different densities of water at different depths, plus perhaps the drag of some barges, explain it as best as is possible under the circumstances.
posted by vidur at 2:52 PM on June 29, 2011
The Potomac is tidal well into DC, and we're a (relatively) long way from the ocean.
posted by MrMoonPie at 7:25 AM on June 30, 2011
posted by MrMoonPie at 7:25 AM on June 30, 2011
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posted by cosmicbandito at 11:53 PM on June 28, 2011