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Channelization is when you straighten a river to make a shorter path from A to B. This makes the water flow faster, since the path is shorter but the volumetric flow rate of water must be the same (because it's receiving the same rate of water from the watershed).

However, that wikipedia article also says,

Channelization has several predictable and negative effects. One of them is loss of wetlands.

No citation and no explanation. I don't get it. Why would nearby wetlands be lost from this process? How could that happen?

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    $\begingroup$ Faster flow of water leads to less infiltration and a straight line of flow, most likely including dams, reduces retention of water during flood events. $\endgroup$
    – Erik
    Commented Oct 29, 2020 at 9:08
  • $\begingroup$ I don't think it'd make it flow faster because the path is shorter, but because there's less frictional impacts with a straighter path? Cars don't go faster on straightaways because the path is shorter, but because they're able to continue to accelerate. $\endgroup$
    – JeopardyTempest
    Commented Oct 31, 2020 at 2:05
  • $\begingroup$ And while eventually the volumetric flow rate has to be the same once it reaches equilibrium (to prevent continual increase or decrease), each bit of water spends longer in the system. It's like greenhouse gases, they cause incoming solar radiation to spend longer in the system, and so lead to a higher temperature. Or it's like if you have every person vote at a voting precinct... if you take longer to process each voter, you're going to have more longer lines, despite the fact the total throughput/output will be the same. $\endgroup$
    – JeopardyTempest
    Commented Oct 31, 2020 at 2:10
  • $\begingroup$ In fact lower flow rate and same volume seems it must occur over a greater area. Because less per second in one area will mean less volume goes through it. So to get the same total amount out, you have to spread it over a larger area, so the slower rate can produce the same total amount. In rough thinking, it seems the units work out that Volume of water moved = surface area of water * flow rate * time... [D]^3 = [D]^2 * [D]/[T] * [T] . $\endgroup$
    – JeopardyTempest
    Commented Oct 31, 2020 at 2:16
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    $\begingroup$ @JeopardyTempest - The elevation change will be the same, but the path is shorter, therefore the straight channel is steeper. I think that will cause faster flow in addition to the lower friction that you point out. $\endgroup$
    – Mark
    Commented Nov 1, 2020 at 2:28

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Channelizing a river keeps it from overflowing its banks as often, which prevents flooding. However, wetlands need a certain degree of said flooding to function as a biome.

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Length of Rivers determines rate of flow. When you straighten a river you increase it's flow rate and make it MORE prone to flooding downstream. Cities try to curb this by turning their rivers into huge drainage swaths (LA river) but ultimately it's pointless. Winding rivers desposit sediments and silt (and nutrients) on lands, those feed wetlands necessary soil amendments they otherwise could not obtain

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What is the purpose of channeling a river, to make it move water more quickly. Moving water more quickly is also called draining water more effectively, If it draining water more quickly the land around it gets drier.

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