I have a ~1 acre pond with a vertical standpipe that determines the water level. The vertical section is about 7 feet and the horizontal run through my dam is about 30 feet.

I just had these pipes replaced since the corrugated metal pipe had rusted out. Both the vertical and horizontal section were replaced with 15" dual wall HDPE and there is a 90 degree elbow connecting the two. I recently learned that the horizontal section *should* have been a smaller diameter.

Is this a big deal? Is my pond doomed to flood the entire world? Would anything else help at this point (such as an anti-vortex plate)?

Thank you

Definitely put an anti vortex plate on it and I would also install a trash rack on the intake side to prevent something going down the stand pipe and getting wedged in there at the 90° elbow.

mousebob,

What was the diameter of the corrugated pipe that you replaced?

How often did your pond discharge water through your emergency spillway under the prior piping system?

Is your emergency/overflow spillway in good shape?

I believe the design reason for the smaller diameter in the horizontal pipe is the proper engineering practice of saving money on the project. Water flow at the top of the vertical drop inlet will have essentially zero head. Flow through the horizontal section of the pipe will have the head equivalent to the height of the drop inlet. Therefore, the horizontal section will flow significantly more water than the flow through a drop inlet of equal diameter.

Your outlet flow will be dependent on the 15" diameter of your drop inlet pipe.

If you are fairly comfortable with your answers to the three questions posed above, then I think you should be fine!

If the situation is more complicated than that, then please post some more information and perhaps someone with far more expertise than myself will drop into your thread.

I believe the advice to install a trash rack and anti-vortex plate are by far your most important factors at this time to protect your pond. A clogged outlet flows NO water!

Thanks for you responses! I actually went with a slightly larger discharge pipe that we had before. It was either 12 or 14" before but it was actually hard to tell because of how rusted out and twisted it was. The emergency spillway was never used unless this main pipe was clogged.

Do the anti-vortex plates aid significantly in discharge volumes?

Appreciate the info!

Anti-vortex plates keep air from being sucked into the whirlpool that develops without the plates. The air replaces water moving through the pipe thus reducing the volume of water the pipe will move per unit of time.

Good deal on your larger pipe!

With a plate and trash rack your pond (and dam) should be safe and secure.

(Maybe inspect your emergency spillway next spring.)