I have a small pond in my backyard, with a tiny outflow pipe that is in the center of the dam. However, the pipe has taken some hits from big storms, and years of erosion have washed out the clay and soil around the pipe. I aim to fix the situation by digging out the pipe, setting it slightly deeper, and then burying it again, planting grass, and forming some type of aesthetic yet functional drain area where the pipe lets out.

My questions:

1) should i replace the pipe with a bigger pipe?
-it is about 9 inches in diameter.
2) should i put the pipe lower than where it was?
-this outflow pipe sat only about 6 inches below the ground
3) bentonite isnt neccesary for the pipe, is it?
-where should i buy it from?
4) on such a small pipe, is an antiseep collar a must have?
- can i make this, or where to buy it?
5) should i dig out the wedge shape to put this pipe in, with the larger side on the pondside? or is this pipe too small?
6) should the pipes get wrapped with anything? sealed together?
- currently there are two PVC 8 foot pipes that lock together.

The pond is about 500m^2 maybe?

The water level only gets to the pipe level during extreme rain events, and usually fills to a point about 1 foot below the pipe. During drought and dry periods, the pond sometimes loses a LOT of water, and stays only about 3 feet deep. But this is rare.

Pictures to follow.

also, totally new to PB, awesome site!

Pretty place! If you are going to be digging up the pipe, I would install a larger one - I'd go with 12" dia by looking at the pictures. The local NRCS office can tell you what sized watershed feeds your pond, and what sized pipe you need for a 100 year rain event. Your tax money at work, so why not try and get some use out of it? I would install the pipe deeper in the ground and install an anti-seep collar. Might as well do it right the first time instead of possibly having to go back and re-do it.

Ditto on what Esshup said. Can you build an overflow area to the side, over natural ground, to take care of a serious flood? Or, just eliminate the pipe idea and go with an overflow?

there is a slight dip to the left of the pipe, that isn't in the picture that acts as an emergency spillway, and it is higher than the pipe. The pipe gets used enough during rainy years that i would be hesitant to take it out, as the discharge can be pretty heavy at times.