Its pretty simple, this is really a gravity pipe plain and simple once the siphon starts. The more weight below the input, the harder and faster it pulls.
Length has everything to do with this as well and since you bought 200' of pipe I will assume you have 200' in the dam, my other calculations were for 100' of pipe. I'm not figuring the friction loss for fittings but 22.5 and 45s are minimal
12" pipe with a 10' drop in siphon mode is 5385 Gallons per minute @ 15.3 feet per second. Now velocity is always figured for a pipe that has valves and a means of pushing the water and the feet per second has an effect called Water Hammer. Lets say I put a valve on the outlet and close it, water doesn't compress so that massive amount of water flowing @ 15 fps sends a " Hammer" all the way to the source. Schedule 40 PVCs safe zone is 5 feet per second with out blowing apart fittings, check valves, pumps, valves, etc in a "Shut Off" situation.
The reason I mention velocity is I'm not sure what that "vee" is buried under ground and you should have continuos flow which should mean you would never see a "hammer" but if its raining in say a 100 year event and the wind is blowing causing waves which may or may not effect the vent ( basically a valve of sorts) of the siphon. I'm probably waaaayyyy over thinking this scenario but say you have a nice steady flow and on the verge of siphon and waves are opening and closing the vent somehow it would be like turning a valve on and off. My guess is this wouldn't happen because you're vent is at water level which is 12" below where the water will be when it starts its siphon therefore needing a 12" wave to create the situation of a possible "hammer"
heres a gravity calculator,
http://www.calctool.org/CALC/eng/civil/hazen-williams_g use them all the time we have a pretty complex irrigation system and gravity feed from one pond to another, to another using 2" rain bird valves to start and stop the flow via a "Dig" solar controller and we see hammer because we have drop as much as 40'
