as far as the riser question goes here the nrcs recommends it to be twice the size as the drain pipe. one advantage of a riser that i like is that it gets rid of the water faster. with no riser if the pond is an inch full you have an inch going down drain pipe. with riser if the pond is an inch full the tube is runnin full blast so you dont need as much freeboard. if you like this method i will try to post a sample of one of the nrcs plans on this pipe start to finish with riser it might come in handy when your able to drain pond for a permanent fix. will try to post some pictures of pictures as you can tell by my thumb in them of a pond without riser on pipe and another of me building a pipe with riser on it. the one without riser does take much less time
