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Removal of Sand From River Beds

10/21/2013 10:05 AM

Can the removal of sand from river beds ultimately affect river flow? Kindly advise.

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#1

Re: Removal of sand from river beds

10/21/2013 10:06 AM

That is the general idea.

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#2

Re: Removal of Sand from River Beds

10/21/2013 11:05 AM

It is difficult to imagine removal of sand from a river bed failing to affect river flow, unless the river bed is dried up (and remains as such) where the sand is removed.

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#3

Re: Removal of Sand From River Beds

10/21/2013 2:33 PM

No. Whatever comes in goes out somewhere, regardless of the disposition of the sand.

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#4
In reply to #3

Re: Removal of Sand From River Beds

10/21/2013 2:46 PM

'No'?

.

How does the goes-ins equals goes-outs conjecture you referenced suggest that altering the river bed would not affect the river flow?

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#5
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Re: Removal of Sand From River Beds

10/21/2013 2:57 PM

Q1 = Q2.

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#7
In reply to #5

Re: Removal of Sand From River Beds

10/21/2013 3:05 PM

Sure, if you want to define it that way.

.

I don't think that model is particularly useful here.

.

Let me ask you a related question: Would you say that building and operating the Hoover dam has affected the flow of the Colorado river at all?

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#8
In reply to #7

Re: Removal of Sand From River Beds

10/21/2013 3:13 PM

Ultimately no; Q1 still equals Q2.

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#9
In reply to #8

Re: Removal of Sand From River Beds

10/21/2013 3:43 PM

I didn't disagree with your assumptions about Q1 =ing Q2, nor did I attempt to to suppress your freedom to arbitrarily define what is or isn't in a system.

.

Let me try a different approach: do you believe arteriosclerosis and resultant changes in flow is a legitimate medical disease/problem?

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#10
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Re: Removal of Sand From River Beds

10/21/2013 3:51 PM

Yes. Closed vessels can be blocked, open valleys ultimately not. Your analogy is amazingly poor.

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#13
In reply to #10

Re: Removal of Sand From River Beds

10/21/2013 6:14 PM

...or perhaps some of your vessels are approaching a blocked state....resulting in amazingly poor flow and insufficient oxygen to areas critical to mastering this simple concept.

.

Whether talking about open-channel flow, or pipe flow; the shape and texture of the material defining the walls of the path affect flow.

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#21
In reply to #13

Re: Removal of Sand From River Beds

10/21/2013 11:22 PM

That is both incorrect and offensive.

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#28
In reply to #21

Re: Removal of Sand From River Beds

10/22/2013 5:29 PM

I assume (and hope) the first sentence (of the comment to which you replied) was incorrect. It was written in jest (hence the emoticon), so please return the offense from wherever you found it (i.e. you shouldn't have taken it).

.

The second sentence is not incorrect. It was also not written in jest. If you find it offensive, perhaps you shouldn't be so defensive.

.

.

The number of responses to this topic willing to completely ignore the path for any flow, insisting 'what goes in must come out' is a bit surreal.

.

Yes, if you force a thoroughbred to breath through a cocktail straw, the amount entering the straw will be the amount leaving the straw....but this in no way means flow is not significantly altered....

.

....the flow will be so significantly altered that a horse comparable Secretariat forced to breathe through a cocktail straw would be no match for a horse like Rocinante in a race of any standard distance.

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#25
In reply to #4

Re: Removal of Sand From River Beds

10/22/2013 12:14 PM

IMVHO (in my very humble opinion) there is no River Flow at all.

Only a water flow in the river, considered that it is a water river.

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#27
In reply to #25

Re: Removal of Sand From River Beds

10/22/2013 2:03 PM

Thanks for dvmdsc 's right correction. It is water flow through river and not river flow.

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#6

Re: Removal of Sand From River Beds

10/21/2013 2:58 PM

It depends on how much sand and how big the river is (among other things).

The answer varies from yes to no depending on the ratio of the two above.

Can you provide more information?

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#11

Re: Removal of Sand From River Beds

10/21/2013 4:06 PM

that can and certainly will change the path of least resistance for the flowing water and increase bank erosion

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#12

Re: Removal of Sand From River Beds

10/21/2013 5:56 PM

Yes. For example, without constant management the Mississippi River would eventually connect to the Atchafalaya, leaving New Orleans dry and ruining it as a port. The US Army Corps of Engineers controls where sand (silt) is removed, if, and when.

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#14

Re: Removal of Sand From River Beds

10/21/2013 6:14 PM
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#15

Re: Removal of Sand From River Beds

10/21/2013 8:37 PM

Dredging increases the volume of water that can be carried in the river, so it should affect the volumetric flow rate - if or when there is actually more water in the river than it was previously able to carry. (Flow of dry rivers, sadly not affected.)

http://en.wikipedia.org/wiki/Volumetric_flow_rate

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#16

Re: Removal of Sand From River Beds

10/21/2013 9:09 PM

No.

There's oh, so much you don't say.

But, no.

It might restrict the flow to the present river channel, but the water's gonna flow, somewhere.

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#17

Re: Removal of Sand From River Beds

10/21/2013 10:46 PM

Sand mining at river mouth where it enters the sea fill facilitate flow.

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#18
In reply to #17

Re: Removal of Sand From River Beds

10/21/2013 10:48 PM

How?

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#19
In reply to #18

Re: Removal of Sand From River Beds

10/21/2013 11:01 PM

In rainy season flooding takes place as water flow is restricted by sand buildup at rivermouth.Dregers are used to remove sand accumulated there.

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#22
In reply to #19

Re: Removal of Sand From River Beds

10/21/2013 11:35 PM

#5

What goes in will come out!

Period! End of story!

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#29
In reply to #22

Re: Removal of Sand From River Beds

10/22/2013 5:38 PM

'...End of story!...'

.

Well, okay. Just so long as you realize it is a story.....

.

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#30
In reply to #29

Re: Removal of Sand From River Beds

10/22/2013 6:05 PM

Based on the miniscule information provided, yes.

What goes in comes out.

Where, was never the question.

And, dredging DOES NOT NECESSARILY affect water velocity.

It MAY affect water LEVEL and it might affect water velocity, depending on the as-dredged shape of the new channel.

Not enough useful information here to drown a rat.

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#31
In reply to #30

Re: Removal of Sand From River Beds

10/22/2013 7:06 PM

The question was not whether or not, '...removal of sand NECESSARILY affects...'

.

The OP asked, 'CAN the removal of sand...affect...'

.

Those are different questions. You seem to agree that removing sand could possibly affect the flow, depending on several factors not specified. That seems to be sufficient to answer 'Yes' to the question actually asked.

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#32
In reply to #31

Re: Removal of Sand From River Beds

10/22/2013 7:14 PM

OK, Yes is a good answer.

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#33
In reply to #31

Re: Removal of Sand From River Beds

10/22/2013 7:44 PM

Note that the word "ultimately" was also in the OP, as well as in some of my posts.

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#34
In reply to #33

Re: Removal of Sand From River Beds

10/22/2013 8:58 PM

Duly noted.

.

Upon reconsideration, with that in mind, I have changed my mind and decided that; you are not wrong; it is just your current answer that is wrong; and that there is hope you might come around to a more correct answer...'ultimately'.

.

.

All kidding aside, I think 'ultimately' only strengthens my position.

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#35
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Re: Removal of Sand From River Beds

10/22/2013 9:47 PM

You seem to be confusing flow with velocity. Shoving some sand around will change the cross-sectional area of (part of) the river, resulting in a change of velocity. But however many cfs are coming down the river remains unchanged, or very nearly so.

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#36
In reply to #35

Re: Removal of Sand From River Beds

10/23/2013 12:01 AM

'...unchanged, or very nearly so....'

.

There is no range of values that qualify as 'unchanged'. Ultimately something is either unchanged or it isn't. 'Very nearly' unchanged, is very nearly the opposite of 'unchanged'. This is especially true when discussing a hypothetical scenario devoid of any specific amounts or tolerances.

.

I do not harbor any confusion about the distinction between flow and velocity.

.

Given your apparent need to condition your response with 'or very nearly so' suggests you do not harbor any confusion about the possibility of volumetric flow rate being affected by alterations to the riverbed.

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#37
In reply to #36

Re: Removal of Sand From River Beds

10/23/2013 3:50 AM

That might have weak merit in some sort of pure math context, but in engineering, it is just insane word games.

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#38
In reply to #37

Re: Removal of Sand From River Beds

10/23/2013 6:07 AM

Dastardly Math! Always robbing the truly imaginative of their glory! Just think how advanced things might be if we had kept Math from always insisting things has to add up!

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#40
In reply to #38

Re: Removal of Sand From River Beds

10/24/2013 4:37 AM

Irrelevant. There is nothing about this problem that requires exact mathematical addition.

But that's no surprise. Hoover Dam was irrelevant, arteries were irrelevant, and the cartoon was irrelevant as well as unrealistic.

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#41
In reply to #40

Re: Removal of Sand From River Beds

10/24/2013 9:54 AM

Okay. Lets go through this methodically.

.

The question was stated as, '...Can the removal of sand from river beds ultimately affect river flow?...'

.

We should be able to agree that if one or more ways in which removing sand from a river bed could affect the volumetric flow in the river, that a reasonable answer would be 'Yes, removal of sand from a river bed ultimately can affect river flow'.

.

Allow me to suggest a few ways this might occur for your perusal

.

1. Removal of sand from the riverbed exposes the relatively impermeable layer of clay below, ultimately causing erosion of this clay, exposing the limestone of the karst topography below. The tannins that cause the river to appear similar to brewed tea, also make the water acidic, so the limestone dissolves. Within a relatively short period of time, the volumetric flow in the river is insufficient for it to be navigable to anything except canoes and kayaks.

.

2. Removal of sand from the riverbed destabilizes the river banks. Erosion soon leads to the banks being breached. As this is a meandering old river, the river banks and the height of the river itself are a good deal above the expansive relatively arid surrounding floodplain. Most of the water that was flowing in the river is now sinking down into the ground in the flood plain. The reduction in flesh water entering the ocean at the mouth of the river has a noticeable effect on the currents and ultimately the amount of precipitation that would normally feed the river has changed.

.

3. Removal of sand from this riverbed begins at the source of this river, a large lake. On distant parts of this large lake, two other rivers also originate.....at least that was the case prior to removing the sand from the riverbed of our river. Deepening the channel, allowed sufficient flow to cause a reduction in the water level of the lake leaving the other two rivers high and dry.... Our river now has roughly the flow that the combined three had originally.

.

4. In a massive undertaking, sand is removed from the riverbed for the majority of the of the river until the river is eventually 1/2 the prior width on average and 3 times as deep on average. The reduction in whitewater rapids and surface area ultimately decreases the water lost to evaporation and the volumetric flow rate is measurable higher than it was previously in the bottom 1/3 of the river.

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#42
In reply to #41

Re: Removal of Sand From River Beds

10/24/2013 10:12 PM

Highly creative, but generally irrelevant.

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#44
In reply to #41

Re: Removal of Sand From River Beds

10/26/2013 12:34 PM

#5 was not an attack. It was clearly hyperbole used for satirical effect.

.

I respect Tornado's opinion, in part because it is so often correct. When I suggested the flow rate of a river could increase because of the volume of tears he might shed after realizing he has been supporting the incorrect argument, It was obviously not serious. No conscious person with even the most loose engagement with reality can grasp that this was not an accusation to be taken literally.

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#45
In reply to #44

Re: Removal of Sand From River Beds

10/26/2013 8:33 PM

Notwithstanding some unusual exceptions, I stand by my original position. For the most part, your weird games tend to misinform the OP.

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#46
In reply to #45

Re: Removal of Sand From River Beds

10/26/2013 11:36 PM

Gentlemen,

I respectfully suggest that it is time to let it go, lighten up, shake hands and move on. I truly believe that no one means to commit any serious fouls here, just fun ones.

Thank you for the past few years of great conversations.

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#47
In reply to #45

Re: Removal of Sand From River Beds

10/28/2013 4:21 PM

Perhaps you could be more specific in your criticism? I am curious what 'weird games' you perceive.

.

I am anxious to see how the weirdness that you perceive compares to the bizarre contortions required for you to maintain your original position that sand removal can not affect flow after being given four solid examples of ways in which flow could be affected.

.

As a note, the examples are undoubtedly unusual because it seemed necessary to exaggerate the effect, because you were having so much difficulty understanding that flow could be affected. There are certainly more subtle versions of each of those scenarios. However, even if there weren't, it would not change the answer. The four examples, which you did not dispute (but rather noted as unusual), illustrate ways in which sand removal can affect flow. If there is any egregious misinforming, it would have our attempt to legitimize sticking with your original position in light of those undisputed descriptions.

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#48
In reply to #47

Re: Removal of Sand From River Beds

10/29/2013 8:45 PM

I understand completely perfectly everthing you have said, and I am tired of your insinuations otherwise.

I think my original answer fits the OP's most likely intent, and I would not change it in any event.

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#49
In reply to #48

Re: Removal of Sand From River Beds

10/29/2013 9:31 PM

'...and I would not change it in any event....'

.

You have convincingly made that point. I have to admit, at first, I thought you had completely avoided my question about your insistence upon your original answer in light of the examples provided. I realize now that you answered the question in the most direct manner.

.

I do not harbor any delusions about understanding perfectly the intentions of the OP nor your own intentions that motivate your comments. I realize there are likely ambiguities and possibly downright errors in the constructed message as well as my perception of those messages.

.

The last few exchanges with you have been very informative and make me realize that my previous interpretation of your comments warrants review and probably revision.

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#20

Re: Removal of Sand From River Beds

10/21/2013 11:08 PM

On a short distance basis, Yes. On a long distance basis, No

When sand or any other material is removed from the river the velocity of the water at that point slows down. As it reaches the end of the removal area the velocity of the water returns to what it would be if the removals were not done.

If the angle of the sand removal location as it meets the unmoved point is steep it can also cause scouring of the materials not removed. This is a problem with dredging of the Mississippi River, New York Harbor as it dredged to accommodate VLCC's with deeper drafts and many other harbors. Another problem is that the contour of the dredged area readily fills with silt which also changes the velocity of the water above it. Fast water velocity tends to remove materials and slow water velocity tends to add materials. Thus, Yes or No.

Good Luck, Old Salt

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#24
In reply to #20

Re: Removal of Sand From River Beds

10/22/2013 9:17 AM

Thats the smartest answer given the information that is missing in the question!

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#23

Re: Removal of Sand From River Beds

10/22/2013 2:48 AM

Interestingly enough there have been several correct answers given that are contradictory to each other because they are standing on only one assumption instead of viewing the situation more holistically. The question was CAN the the removal of sand ultimately affect the river flow. From a theoretical perspective the correct answer would be yes.And in all honesty the real world answer would likely be the same. Dredging material and changing the river channel and thus affecting the stream morphology almost always has a noticeable flow effect. Along with this you will often see a lowering of the adjacent areas water tables as the river draws more water from the surrounding area. This additional water equates to increased stream flow which usually results in higher velocities, increased sediment transport etc. And we haven't even thought about water quality or habitat issues here. Dredging is never something to be lightly considered. Consult some knowledgeable local hydrologists if possible.

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#26

Re: Removal of Sand From River Beds

10/22/2013 12:28 PM

Not the volume, only the velocity......It's the ecosystem that can be devastated...

http://shodhganga.inflibnet.ac.in/bitstream/10603/8987/11/11_chapter%207.pdf

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#39

Re: Removal of Sand From River Beds

10/23/2013 3:40 PM

Rivers are pretty complex (mechanisms?). It takes many years for them to make their path in the landscape. When I was working in Belgium for the Laboratory of Water engineering, we had a complete scale of the rivers there and especially the river Scheldt (De Schelde) was very important because those days, it was the driveway for (then) Europe's biggest Port. The Scheldt has a very big meander between Vlissingen and Antwerp and many scenario's have been worked to redirect the river and eliminate this 2-3 hour detour.

As some posters here said, velocity is important.

Depending on the nature of the river, it transports sand and sediments where the velocity is high enough and drops it where it is to low to keep it in suspension.

Often, when dredging, the sand just comes back over time, because there the section is bigger (more depth- width or whatever) and the velocity drops.

Water Civil engineers, get info about all the parameters and determine how much can be dredged within a reversible cycle. Otherwise the river will be effectively re- engineered or modified and start to build on its new equilibrium.

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#43

Re: Removal of Sand From River Beds

10/24/2013 10:31 PM

Sand mining is a lucrative business not only in riverbeds but also in beaches and other locations for building construction,landfills etc.Politically influential persons are engaged in this work & make millions. Even across state borders they do it in some countries. Unless government takes action,it will continue. If waste material from demolished structures are crushed & recycled as well as flyash etc are mixed with concrete it will continue. Government should demarcate areas for this.

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