If your ponds are mostly excavations built on gently sloping terrain with small water shed you most likely don't need a pipe. if you decide to use a pipe 6 inches is too small because it will tend to clough up. The NRCS in my area uses 12 inch PVC with seep collers for smaller water sheds. If your only talking about 10 to 20 acre watershed this should be more than adequate. I installed 18 inch ADS plastic pipe in my pond it was cheaper than the 12 inch pvc. Good luck
