Hello John;

There's a brief yet v. useful discussion on Preissmann (hypothetical piezometric) Slot vs. Standard transient pipe flow approach by B.C. Yen & A.O. Akan in chapter 14 of the Larry Mays "Hydraulic Design Handbook", Mc Graw Hill,1999.

Good Luck!
Mostafa Bozorg-Zadeh(ICE)
bozorg@KOSAR.NET