By Dennis W. Jackson, P.E., Lead Software Architect for Joseph E. Bonadiman & Associates, Inc.
Example Study
To compare the two programs, an identical hydraulic analysis was performed to compute the hydraulic grade line in a fairly small improved channel section. This channel, only 300 feet long, starts at the system outlet with a standing water elevation of 98 feet with the invert elevation is at 90 feet elevation. The channel shape is trapezoidal with a junction and a culvert crossing with 2 pipes in parallel. The channel is curved with a varying radius of curve except through the culvert section. The system head-works is a side-outlet from another channel with a fixed water surface of 102 feet.
Data entry with the WSPGW program for this channel only required 11 relatively simple entries. The HEC-RAS program data entry required many more entries, including adding additional cross-sections to correct and minimize the error and warning messages. The following drawing shows the results from both the WSPGW and HEC-RAS programs:
The WSPGW program prepared the plan and profile views of this drawing.
Note: In this open channel example the program results of HEC-RAS and WSPGW are nearly identical. The three hydraulic jump locations were nearly the same, and in the HEC-RAS analysis the jumps were given the length from the user input section which supported super-critical flow to the next user input section. The culvert analysis yielded the same results at the entrance and exit of the twin pipes.
In this example of a curved channel, the super-elevated water level on the outside of the channel curve(s) is a factor to be considered in the channel design. The WSPGW program calculates this elevation and applies a safety factor if the channel is other than rectangular, or if the flows are in the super-critical regime. The WSPGW program also draws this data as shown in the plan and profile views.
