If im using 18" round corrigated plastic pipe through my dam as an outflow....do I need to install an anti-seap guard/collar as well? Isnt that why the corrigated pipe is corrigated?

I didn't. There should be no need for one as there is virtually zero hydraulic pressure to force the water. When packed correctly, corrugations on pipe act as mini anti-seep collars. Emphasis on "packed correctly".
Now, on a pond drain...this is a different matter. Anti-seep collars are a wise investment there.

I agree with Bski in that pipe corrugations are mini anti-seep collars however; I would still install at least one and probably TWO 48 X 48 inch collars.

If water eventually makes its way along the pipe for any reason, the results are catastrophic.

Pretty cheap insurance!

Ed

I'm with Ed on this one. The anti-seep collar kits I used were about $40 each, IIRC. Installing four of them (2 on the drain pipe and 2 on a 1" water line) took about 2 man-days (mostly recompacting the core around them and the pipes with a gas-powered tamper, which we would have done even without the anti-seep collars).

I assume we are talking about an 18" corrugated plastic primary spillway pipe thru the top of the dam. I did exactly the same thing, never even considering an anti-seep collar. We'll see when pool arrives, I guess.
Either way, I relent to Ed's wisdom. B-ski going 10-10 and on the side.

Instead of buying anti seep collars you might consider applying wet/dry mastic to the pipe and pouring quickrete around it while the mastic is still wet. Then, maybe mix the backfill for the pipe at the face of the dam with some bentonite before compacting it in. This is what I did for my bottom drain on smooth walled pvc and so far it works great albeit I only have 6 ft of head on it at this point. (picked up almost 2 ft last weekend) I poured 2 3' x 3' seep collars by ditching out for the bottom half of the collar perpendicular to the pipe, then forming up for the top half. Should work great on corrugated pipe. I looked at a pond where a collar such as this had been on a bottom drain for 5 years with no problems so decided to try it myself.

TN Hillbilly,

You bring up a good point on using heavy (trowel grade) mastic (tar) on smooth pipe. This is especially true for pvc and poly pipe. It can be difficult to keep water from finding its way along smooth pipe surfaces. I have seen entire lengths of pipe coated with this material and it works very well in low head situations. Increase the head pressure on the pipe and just add a couple cut-off collars, “PRESTO” very workable system.

Ed

Good place for antiseep membrane is Home depot ask for shower pan membrane and they will cut you what size you need A 4x8 piece of pressure treated plywood this will make two weep collars.On pipes under 24 inch we use a childs plastic saucer sled and silicone. Portland cement can cook some mastics

face72,
Good ideas & advise above.
Corrigated pipe is corrigated only to add strength.

60" x 60" rubber anti-seeps are standard around here. Cut a hole an inch smaller than pipe and squish pipe thruough the rubber. If done properly there will be an inch of rubber around the pipe to hose clamp which gives a very good seal. Pipe with anti-seeps
30" x 30" for stockwater pipes. 2" stockwater pipe with anti-seeps

There is really not much expense in the collar and the less your pipe seeps the better off your are.