Pond Boss Forums POND CONSTRUCTION Building a dam Increase spillway pressure outflow

I would be grateful if someone could give me advice on building a spillway that can generate enough output pressure to force water through a pipe in order to gain adequate head pressure to turn a water wheel. The pond is a 1/4 acre pond built on a spring that has continuous flow. At the back of the pond there is a pipe about 2 feet in diameter where water flows out at approximately 5 gallons every ten seconds (I couted to ten while holding a 5 gal bucket). CAN THIS PRESSURE BE INCREASED TO BE USABLE? A quick google search yielded something called a fusegate. I don't know much about this device but it sounded great. I need a waterfall but don't have one. I would like to get at least 3 to 5 ft of head out of the thing. I have 3 brand new pallets of bricks and can buy PVC pipes but need a great plan. Please help.

Welcome, Summertime! There are some awfully sharp minds here - soil guys, engineers, and guys who just plain have a knack for this sort of question. Someone will be along with an answer, I'm sure, so just hang tight and wait for input/questions!

Hello, summertime.

The only way to increase the pressure on your outflow (for "free") is to increase the "head" - vertical distance between the water level in the pond and the elevation of the outflow. So you can raise the water level (non-trivial for most of our ponds) or lower the output.

If you have a near constant outflow, you could have it enter a smaller pipe at any level below the pond surface (to ensure that this pipe always receives the water first, preferentially wrt the 2 foot diameter main drain) and tap into it's outlet far enough below the damn to suit your needs. If you have enough drop behind (below) the dam.

If you want the water wheel turning for ornamental purposes, you could of course pump water to it.

Summertime, I did a fair amount of research into deciding whether to try to generate hydro power from my spring flow. First, Theo is correct that your "head" is governed solely by the distance between the top of the water and the outflow (minus a small amount for friction loss). Thus, your pressure can't really be increased without raising your pond level or lowering the outflow. As for whether your pressure it "usable," it really depends on what you mean. You won't generate much power with that flow. Your flow might generate a little power if you could get a lot of head (at least 10+ feet), but is probably not going to do much more than provide some ornamental value if you lack a big drop on the back side of the pond.

Just had this thought in reading the posts here again - could you just neck down the size of your outflow pipe to gain additional pressure to turn the water wheel? I don't know if that would work from a physics standpoint or not, but it seems like that's the concept behind a garden hose nozzle to some degree. Another potential issue that comes to mind is that if the outflow pipe diameter is reduced, I guess there's a chance that it wouldn't keep up with the flow entering it on the pond side and could eventually result in water levels rising to the point that water overflows your dam.

See? This is the hazard of a non-engineer playing around at offering an engineering-type fix!

To produce electricty? or for some kind of asthetic appeal? haha

I've looked into it quite a bit. You probably need a decent elevation change in addition to flow. Look up a pelton wheel turbine, theyre moved by 2 nozzles pointing in opposite directions. For microhydro I think the nozzles are pretty small maybe 1/4 inch.

The turbines are much more effecient than wheels. What you have would probably work IF you have the elevation change. I am tempted to try it if I can bolt a car alternator to one. Plus I think there is an issue of making it self exciting or it wont turn the alt at all.

Got here late. Love this idea would like to hear more.
If it only ran a pump or some lights I would likr to see it.

summertime, just to give you an example, with your 30 GPM, and if you could have it piped to a turbine with a 12 ft. drop, your max. power output would be about 35 watts.
I've also looked into micro hydro but not really economical unless you have lots of flow or large amount of head, or good combination of both.

Decreasing the pipe size will increase velocity not pressure, flow will be reduced as velocity increases, IIRC.

Flow equals area times velocity ( Q=AV ) , so decreasing area increases velocity. I think you recall correctly. Pressure depends mostly on height and friction loss. But I aren't no engineer.