Pond Boss Forums INTRO Questions & Observations Spillway vrs Drainpipe

For a 1.5 acre pond 20 ft deep with a live spring would a concrete spillway discharging onto riprap be better than a drainpipe?

Does the pond also receive large amounts of surface water during rain events, or does the pond have raised banks and the spring is the ONLY water that enters the pond?

Need both in my opinion.

Agree with jludwig.

Both would be great on a good budget, but if the budget is a concern...FishinRod asks a good question. With no watershed and a relatively consistent spring flow...a drainpipe alone would do fine. It's never a bad idea to design in an emergency overflow, but concrete might be overkill. My small pond utilized the emergency overflow this year after a 6" rain in 2 hours. It flowed over the dam at the designated grassy section for about 4 hours (I have too much watershed - 25 acres when it should be closer to 2-3 acres). Minor amounts of washout occurred well below the dam, but all was good. My 15" pipe was not enough to allow the 3 foot of water rise to escape fast enough...mostly due to the 1/2" mesh I have on it to keep the fish in during normal heavy rains. It clogged with debris pretty quick and over she went.

For my 1.8 Acre BOW, I have a 20' wide spillway, with 3-4" tall bermuda grass. 6" in 2-3 hours off of 35-40 Acres of watershed ( all grassland ) , 3 days of overflow and the bermuda acting like over lapped shingles , NO damage, no ruts, it never clogs . Very happy with my spillway . But, the dynamics of each pond , of each watershed is different . It all depends , probably applies . I've hired a professional dam builder for both of my ponds, who's primary income for last 50 years has been Federal water shed control dams .
Hire a professional . If going with spillway, maintain it .

The pond will mainly receive water from a 60 gpm constant flow spring. There isn't a lot of watershed during heavy rain. Years ago NRCS said a drainpipe less than 12" would suffice for this pond site. 5R is a pond builder in Buffalo Texas and suggested primary and emergency spillways rather than pipe.

A 2" PVC pipe would pass 120 GPM! (Modeled 20' long, 5' drop)

However, that size of pipe would be easily plugged with debris.

You have lots of easy options for your pond!

Maybe a 6" angled pipe through the dam with good protection against debris on the inlet side.

Maybe a 4" siphon with an air vent for automatic level control.

Do you live at the pond? If so, then your emergency spillway plan sounds like overkill to me. (And I hate not having a good emergency spillway.) However, if you live there and notice after a day or two that your outlet pipe is not functioning correctly, then you should be able to readily fix it.

If you DON'T live at the pond, even if your pond overflows, then 60 GPM is not capable of too much damage. A tiny emergency spillway of some type should enable your dam to survive with no damage until you notice and repair the main outlet.

However, you (and I) could be wrong about the amount of watershed that drains into your pond.

Have you ever observed your pond after a very large rain event?

I've wondered why an emergency spillway would be required if there is a proper wide primary spillway?
I guess it's possible the primary could get stopped up.

Typically, the main pond exit is a pipe while the emergency spillway is an open area higher than the primary overflow but below to of the top of the dam that is located beyond the dam on a gentle slope to avoid erosion. The emergency spillway is intended to carry much larger volumes of water than the primary spillway but gets used infrequently.

With a grassy spillway or a dirt spillway, it will erode over time where an outlet pipe (providing it isn't made from corrugated galvanized steel) won't.

The emergency spillway needs to have a dense mat of roots from grass to prevent it from eroding in times of use.

Water is a universal solvent. It WILL chew away at a spillway if it is used constantly. If a pond builder recommends a dirt primary spillway, get it in writing that he will come back and repair it at no cost to you if it fails or erodes.

The pond builder recommended two concrete spillways each with riprap for primary and emergency drainage. I do not live at the pond site but usually go there a couple of times a month.