Flow Advisor, from www.pipeflow.com, provides many options for solving flow problems including V-notch weirs, common in water and wastewater clarifiers, flat-bottomed channels, etc. A screen shot is shown below. In this example we have a steel pipe, 2,500 feet in length, with a 4-inch internal diameter, and a pipe drop of 30-ft over the 2,500-ft pipe run. Note that there is no head pressure. We can see in the screen shot that the flow in this pipe is calculated to be 101 gpm. This is yet another handy, very easy-to-use program.
Flow Advisor Screen Shot