Inverted Spillway on a Lake

I think you must be referring to pond aeration to prevent water stagnation...

One year update...

https://www.thepondguy.com/category/pond-and-lake-aeration-systems

Not exactly.The inverted spillway has no depth limit,and requires no electricity,and also prevents freezing of the spillway in the winter. It removes the stagnant deposits and old water from the bottom of the pond,and this is replaced by fresh oxygenated water from the water supply source,a more efficient means of clearing the water.

I did a Google search on an "inverted spillway" and got only information about dam spillways and their reservoirs, nothing regarding a lake nor anything calling itself an inverted spillway. It seems you know more about this topic than anyone else. You should write an article about this for CR4.

A citation where one of these spillways was made or discovered would be nice, too.

I saw it on an outdoor fishing channel,and the fisherman asked the guide,the lake owner,how he kept it so clean and clear when other lakes in the area were cloudy,and he explained the inverted spillway system he had installed.

Here is a link to a bottom withdrawal spillway.

https://extension.missouri.edu/publications/g1530

It appears to me that you are siphoning the "dirty" water from the bottom of the pond. The pond needs to be elevated so that the siphon has an exit lower than the pond. Most ponds, I believe are at the lowest elevation in the vicinity.

The siphon would continue to drain the pond until the pond surface reached the siphon entrance unless there is someone to close the tap at the siphon's exit when clean water starts coming out.

I would call that a siphoning system, which requires elevation drop from the pond to the irrigation field, or crick...Unless you have regular rainfall, I don't see this as an entirely reliable system as your siphoning is only available after a significant rainfall...and where I come from the algae grows on the top of the water as well as at depth...any significant amount of algae is going to clog the pipe anyway...what you need to do is balance the ecosystem of the pond/lake with some fish that eat algae and are compatible with the local environment....

https://nualgiponds.com/algae-eating-fish-for-ponds/

Interesting thought. I have been using a similar method for the last 30+ years in my rain water tanks. The overflow is taken from the bottom of the tank and is close to the water take off point thus removing sediment that would normally get into the filtration system.

The overflow consists of an elbow on the bottom of the tank and a short pipe to take it towards the takeoff. The elbow is connected by a riser to near the top of the tank where it connects with the original overflow point through a tee open to the top.

The open tee stops syphoning and at the same time acts as a top overflow, the system works well during high flows causing a full tank. We have no weed killer, sorry I mean town water out here, dirt roads, and a power station/mine adding to the dust landing on the rooves.

Same design used here for domestic water tanks at our place. As you say, must have the syphon breaker at top of the outlet, or simply empties the tank.

Some people also use a "first flush" diverter that diverts the first "dirty" water into a separate chamber before the roofwater goes into the tank. Those often have a 3mm bleed hole so they automatically empty before the next rain event.

For our farm dams, we installed a "silt trap" that was typically a smaller dam around 5% of the capacity of the main dam for heavy sediment to drop out of the flow. These were then easier to clean that the whole dam and the main dam was not contaminated during the cleaning.

Each "system" has merits provided that the people responsible understand the intended operating methodology.

I have my own first flush system installed consisting of a tee and 90mm downpipe to catch the first water flows from the rain. Also the catch dams are on most of our dams on the rural block and well as the farm. amazing how much silt gets caught in a year though now most of the flows are over grassland so the sediment flow is filtered out long before the dams in the contour banks.

What I am referring to as a spillway is an overflow pipe or structure that is positioned to drain the water when it is over the pipe or structure top.The drain outlet is on a lower level than the pond,of course,(common sense). No siphoning occurs below the set level of the overflow.Most farm ponds are stream or spring fed and are not reliant on rainfall,but rain does affect the level of course.

There are plenty of ponds on hillsides,many feet above the surrounding terrain.

These ponds are fed by water from shallow underground springs flowing downhill.

They are sometimes dug in the middle or top of a running stream.The spring fed ones rely on a shallow surface water supply,or Artesian wells drilled for that purpose.

The Artesian wells provide very clean water,clean enough to drink.

It is actually too clean for most fish,and must be fertilized to encourage fish health.Plenty of these in mountain lakes.

A spillway that pulls from the bottom will not siphon below the level of the outlet pipe with a simple vacuum breaker installed in the cap.

My grandmother had a spring fed trout pond behind her house,where she would keep the trout she caught from a local lake to "clean them out", as she said.

They fertilized the lakes with turkey house sweepings,and she fed them biscuits and laying mash for about a month before eating them.It was nice to go out the back door,put a few bread crumbs on the water,then select the trout you wanted for breakfast with a dip net.

Delicious!

Those were the days!

Actually, now that I think about it, there is a retention pond just down the street that fits your description. When there is a lot of rain, it overflows down a bank and into a creek.

There are a number of these ponds whose purpose is to slow down the stormwater (and silt) draining back to the nearby lake from whence our drinking water comes. After a while, the ponds tend to silt up. (We got a bill a few years back from the HOA for dredging one of them.)

I don't know if a siphon would remove this silt and how it could be loaded into trucks for removal.

An inverted siphon discharge has its pros and cons.

Every pond, regardless if it has an inverted siphon discharge or not has to have a weir at the water static water surface so that in the event of a major rain or melt event, the excess runoff can be discharged without causing dam failure and causing flooding due to high water levels. An inverted siphon discharge has limitations on it conveyance capacity caused by the tube diameter. To construct an inverted siphon discharge to meet the necessary flow capacity of a major rain event would be very costly.

Because the pond has the weir for emergency discharges, the cost of a second discharge point is often figured as a "luxury".

An inverted discharge must have an air break in it. Otherwise, the siphon will draw the pond down to the level of the intake. I am pretty sure you included that in your description so I am not intending to nitpick.

During the summer when a thermocline is established in a pond an inverted siphon draws the water that has lower oxygen content and potentially more sediment. However, storms (wind and significant inflow) can mix the water up and the thermocline has to become established again.

The more polluted water is not necessarily on the bottom. It really depends on the pollutant being measured. An inverted siphon discharge will not remove floatables, many carbon related pollutants, and blue green algae that does float because they are on the surface.

In my opinion, far better than an inverted siphon discharge is to discharge from the bottom of a pond by gravity and put a valve on it to throttle the flow or stop the flow. That way, the discharge of pond water can be managed so that water can be take from the surface or from the bottom of the pond. For a lot more expense, this process can be automated. Hence, automation is only done for very sensitive waters or where the income generated by the dam allows for automation to be paid for.

I respectfully think it is incorrect to state that most farm ponds are not reliant on rainfall. A generalization like that would be true at a local level. Even at a regional level for certain regions, particularly for many Eastern regions that have stable ground water levels due to regular and fairly reliable precipitation. But to say "most" in regards to even a multistate region seems to be generalization that should not be taken for granted when building a pond.

Almost any surface body of water is affected by rainfall, inflows, outflows, sunlight, nutrient levels, the land use of the contributing watershed, ground water quality and quantity, air pollution, etc. It is all one big interconnected system the brings water to a pond and then, by discharge, takes the water from that pond and directs it downstream.

And remember, whatever one pond discharges, the down stream has to deal with.

I believe what is key is that a well managed pond, versus one that is ignored, will have better water quality. Hence, better recreation opportunities and a better habitat for preferred species.

Everything has it's pros and cons.The top of the outside pipe does not have to be very high above the normal fill level of the pond.A mere 2 inches or so will suffice.

It is best to design this from the begging stage for sufficient clearance between the two pipes or spillways.

Any heavy rainfall will simply go over the outside standpipe and out the normal way.

Yes,my statement was a broad generalization of local farm ponds,not intended to be a world-wide ranging statement.

I have seen ponds designed both ways,and seeing is believing,the bottom suction is much cleaner water.

Most suppositions are made out of a magical melding of ignorance and imagination.

"Imagine an open spill way pipe with another larger capped pipe surrounding it but the open end mounted slightly above the bottom of the lake."

Can you draw that?

Cant draw it ,but imagine a small pipe connected to a drain pipe.The top of this pipe is level with the top of the lake or pond when the pond is at it's maximum level..As the water rises,water from the top will go into the pipe.Bottom water stays on the bottom and stagnates.

Now insert a larger pipe over the small pipe,higher above the water than the small pipe with the end of the larger pipe elevated above the bottom of the pond or lake.

Now the water that leaves the lake as the water rises comes from the bottom of the lake instead of the top,and is replaced by fresh incoming water from the water source .

This will tend to remove sediment from the bottom of the pond or lake.

If you are in a mild climate and do not worry about freezing,a cap is not required,otherwise a cap with a vacuum breaker is required.

Now,clear as mud?

I suspect that the OP is describing the second of these.

Variation of two types as follows

With the entrance pipe extended to the "bottom" so that flow comes from there and will bring silt with it.

Or

But with a sleeve around the intake so that water is drawn "up" from the bottom of the sleeve.

Diagrams from the following.

8 Most Common Types of Spillways (With Diagram) (biologydiscussion.com)

Might it be operating under the same principle as a Pythagoras Cup?
https://www.youtube.com/watch?v=A-YMHXuiaWw
regards,

Vulcan