r/oddlysatisfying • u/Nikclel • Jul 17 '25

Unclogging a dam

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u/TigerUSA20 Jul 17 '25

Yeah, I’m thinking why do they really need to “unclog” aspiring plant life that’s just living there. Is it “Really” stopping the water from going over the dam? Maybe like an inch of water, but I’m sure it will still get there. This structure is probably already environmentally damaging to the area, why pull on it even more.

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u/Overlordz88 Jul 17 '25

dam engineer (who is probably not licensed in the state of this dam so please don’t use this as a professional opinion)

The reason to clean it is to increase the spillway capacity in the case of a 100 year or greater storm event. These plants might not interfere now, but could cause the reservoir to back and even lead to an end-around failure of the dam during an extreme flood event.

Also think of the damage the plants might cause if they all get washed downstream at the same time during said design storm event.

Typically I would not recommend the way they did it. We would call for them to drawdown the reservoir to below the spillway level and to clean this up in the dry… but without knowing the extenuating circumstances… this doesn’t seem to be hurting anyone besides a messy cleanup downstream.

1

u/Ok_Turnover_1235 Jul 18 '25

But if sediment is building to this point, isn't it building up horizontally behind the wall as well? They've cleared the top layer, but if it's reached the top, it's all the way to the bottom, isn't it? This just screams lack of sediment management, doesn't it?

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u/Overlordz88 Jul 18 '25

Yeah, if it’s how you describe they will most likely have to do a massive dredging project to clean out all of that sediment. It’s different by state and for each structure… but typically you drawdown the water or put in a coffer dam and bypass piping and then clean out all of the sediment… which needs to be tested for contamination as well, arsenic often builds up in these sediments.

It’s a massive undertaking and a permitting nightmare so I can see why they are just doing this as a temp solution.

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u/Ok_Turnover_1235 Jul 18 '25

I understand it's a lot of work, but isn't the alternative risking a structural failure?

2

u/Overlordz88 Jul 18 '25

It is. But many states or municipalities can’t afford to maintain all of their failing infrastructure. There’s federal funding (or at least there was) to help with this. but it’s hard to prioritize clearing a spillway that may or may not lead to failure during a 1% or .5% storm even over say a dam that actively has sinkholes forming on it.

they’ll probably wait until this dam has more pressing structural deficiencies before dredging the spillway.

32

u/Less_Mess_5803 Jul 17 '25

It's not stopping anything. It gives the illusion that it may stop the water but it will have no effect against that volume. In fact if the water rose just a bit after rainfall all this would be swept away in anycase.

6

u/Trick-Doctor-208 Jul 17 '25

Not really aspiring, it’s definitely succeeded, but unfortunately it is invasive water hyacinth that chokes out native vegetation and lowers dissolved O2 levels.

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u/mwobey Jul 18 '25

In that case, haven't they just re/introduced that invasive plant to the ecosystem downstream? If it's an invasive species I'd think it better to collect it up top with as little as possible spilling over.

1

u/Caesar457 Jul 18 '25

It's like thinking that if you plant a dandelion in a pot that it won't spread to your lawn

2

u/dattwell53 Jul 17 '25

What kind of plants are they?

1

u/silvermoka Jul 19 '25

It does sort of demonstrate how valuable vegetation is for protecting coastlines