Natural Bottom Release Dam Effect

[jsb95]

There’s a lake and dam near where I live, and the top spillway is dry 80+% of the time. However there is a medium sized stream that begins about 200 yards down from the dam. I’ve noticed that during dry periods where the spillway is dry, the water seems to emerge from the ground in the stream-bed in the same location.

The water there is cold, like ground spring water. Has anyone else observed a similar phenomenon? My guess is that the water table and pressure from the lake creates a spring-like groundwater effect. Of course, this section of the creek is probably 50 feet vertically below the dam, so that kind of makes sense.

Has there been any research in this dynamic? I suppose it also has to do with the soil and bedrock makeup.

 

[CRB]

Could be a sign of a future dam failure.

 

[Fish Sticks]

There’s a lake and dam near where I live, and the top spillway is dry 80+% of the time. However there is a medium sized stream that begins about 200 yards down from the dam. I’ve noticed that during dry periods where the spillway is dry, the water seems to emerge from the ground in the stream-bed in the same location.

The water there is cold, like ground spring water. Has anyone else observed a similar phenomenon? My guess is that the water table and pressure from the lake creates a spring-like groundwater effect. Of course, this section of the creek is probably 50 feet vertically below the dam, so that kind of makes sense.

Has there been any research in this dynamic? I suppose it also has to do with the soil and bedrock makeup.

This is essentially the what beavers did for the entire country before we almost killed them all. On smaller scale large woody debris does this too by accumulating cobbles and graves around them on the upstream face of the debris. it forces water into hyporrheic exchange zone and you get upwellings behind the woody debris that preferential ground water spawners like brook trout like to spawn in. You can see ground water type plants behind islands formed by wood in freestoners illustrating this phenomenon

 

[troutbert]

Interesting. Where is this?

Do you mean that 80% of the time there is no flow from the impoundment to the stream below other than this groundwater?

I agree with the post above that this creates a danger for dam failure.

 

[jsb95]

This is essentially the what beavers did for the entire country before we almost killed them all. On smaller scale large woody debris does this too by accumulating cobbles and graves around them on the upstream face of the debris. it forces water into hyporrheic exchange zone and you get upwellings behind the woody debris that preferential ground water spawners like brook trout like to spawn in. You can see ground water type plants behind islands formed by wood in freestoners illustrating this phenomenon

That was my thinking exactly

 

[jsb95]

Interesting. Where is this?

Do you mean that 80% of the time there is no flow from the impoundment to the stream below other than this groundwater?

I agree with the post above that this creates a danger for dam failure.

Pinchot lake. How deep are the foundations for dams? I’m thinking that a healthy ground water system could go under a dam without necessarily damaging the integrity of the dam itself- but I understand your thinking

 

[FrankTroutAngler]

I'm not familiar with Pinchot Lake, but all of the impoundments in the Altoona area have minimum flow requirements so that the stream doesn't go dry below the reservoirs. Is it possible that there is a minimum-flow pipe buried under the gravel where the "stream" emerges? If not, I would guess that this is caused by non-native, invasive brown trout stocked by the PFBC because these brown trout seem to be the cause of every problem.

 

[troutbert]

I'm not familiar with Pinchot Lake, but all of the impoundments in the Altoona area have minimum flow requirements so that the stream doesn't go dry below the reservoirs. Is it possible that there is a minimum-flow pipe buried under the gravel where the "stream" emerges?

Does this sort of minimum flow pipe coming out of the bottom of a dam exist on other dams?

It's an interesting idea, because the water would be cooler than water from the very top of the lake flowing over a concrete spillway. But I don't know if it's ever been done.

People say that small impoundments don't have temperature separation, but anyone who has gone swimming in Lyman Lake or Poe Lake or similar places know that the water on top is far warmer than the water several feet down.

 

[Fish Sticks]

I'm not familiar with Pinchot Lake, but all of the impoundments in the Altoona area have minimum flow requirements so that the stream doesn't go dry below the reservoirs. Is it possible that there is a minimum-flow pipe buried under the gravel where the "stream" emerges? If not, I would guess that this is caused by non-native, invasive brown trout stocked by the PFBC because these brown trout seem to be the cause of every problem.

Lol yea everyone knows the top 30 most invasive animal on the planet out of 4-5 thousand that has extirpated or reduced amphibians, Himalayan snow trout, moto sucker, bluehead sucker, endangered humpback chub, endangered candy darter, endangered sandy river crayfish, hellbenders, razorback sucker, golden rainbow trout, Ghila trout, galaxids, apache trout, brook trout, multiple cutthroat subspecies, entire macro invertebrate populations, and many more on every continent except antartica outside their native range has zero negative effect on the environment here in PA where our state just doesn’t study it……..lol duh