Russ,
A Nebraska Base Drawing can be viewed at.
http://efotg.nrcs.usda.gov/treemenuFS.aspx?Fips=31045&MenuName=menuNE.zip After fixing this horrible address to your browser; Select Section IV; D. Jobsheets etc.; NE Standard Drawings; Then "Concrete Base Metal Pipe Riser and Alfalfa Valve drawdown facility'.
I hope this works for you as the drawing is pretty much self explanitory.
If you have difficulty navigating to this site; to answer your question.
The pipe riser is connected to the pipe barrel and is at least 1.25 times larger than the barrel. The pipe barrel will not flow full during a large storm event if this practice is not engineered into the riser and barrel. The 10" drawdown pipe, with alfalfa valve attached, elbows up at a 90 to enter the riser from the bottom. Concrete is poured to secure all the assembled pipe etc.
With a key, at least the length of the riser, you can open and close the valve.
Hope this helps,
Ed
