Hydrocad questions 1

[Karstman]

Hydrocad is a great program and I use it every day. However, I wonder why the minimum dt is 0.01 hr. For many projects I see, this means that simultaneous routing will not work because oscillations almost always occur. I would like to see a minimum dt of 1 second like PCSWMM and this would make it an even more useful tool.

Also, at least one recent paper dealt with values of Ia/S and the authors claim that the ratio should be 0.05 instead of 0.2. I haven't found a way to change the ratio in Hydrocad. Is this possible, and if not, why not?

 

[TerryScan]

Like most hydrology software, Hydrocad implements standard models. To my knowledge, the accepted standard for Ia/S in SCS methodology is 0.2. The one paper you mention suggests plans for revisions to this standard. However, at this time it has not yet happened. When it has been officially changed, I suspect Hydrocad, as well as other software packages will make the change.

If software allowed the user to change all aspects of the computing parameters, it would be difficult for the software to claim it is complying with standard calculation methods.

For example, in my area (Delaware), we are compelled by law to utilize the Delmarva Unit hydrograph in most of the state (not simply because it is supported in a paper). Hydrocad does supply this option when utilizing the SCS method.

 

[psmart]

The next HydroCAD 7.1 release will allow the Ia/S ratio to be changed. However, this change must be made with extreme caution, since you will be deviating from the accepted standard of Ia/S = 0.2

You can use a smaller time increment with HydroCAD by setting up a custom units-definition file. However, we have rarely (if ever) found values smaller than 0.01 hours to be useful. If you feel the need for a smaller value to improve routing stability, you should first try the dynamic-storage-indication routing procedure, which is inherently more stable than the simultaneous routing.