Pond Boss Forums POND CONSTRUCTION Building a dam Stand Pipe and Overflow Pipe?

Ok, I have been pondering this stand-pipe thingie (oh geeze watchout) and I dont understand the intention of the standpipe design. Granted, I had a stand pipe, so I am not knocking what works. It works. But why would you NEED a stand pipe. What does it's design provide that a drain pipe does not provide?

I keep thinking about "why would you put a hole in the bottom of your dam" - there must be a good reason. What is it?