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General Questions re output & Link representing river elevations

General Questions re output & Link representing river elevations

General Questions re output & Link representing river elevations

I'm reviewing Hydrocad output that was submitted to our local government as a substantial portion of plans for a new development. Is it typical for a developer to provide the .hcd files? I know that Hydrocad was designed to keep the model files small so that they could be emailed, but do developers typically do this? I would like to have access to this file  so that I can run the model myself, make changes where I have questions, and thereby assess the impact of various model design choices. However, I suspect that the developer may be somewhat unwilling to provide these files, so I want to know if this is a typical practice.

Also, the developer modelled several design storms (2, 10, 25, 100). However, they *changed* the model for each design storm. As an EE who performs simulation regularly, my training has been to create a static model that is then run for various input scenarios. Determining portions of the design that behave differently between the different input scenarios is actually the purpose of running the simulation, and those behaviors are assessed for their different impact on output. When a model is changed for each input scenario based on assumptions about behavior in each, doesn't that muddle the very purpose of the simulation? Is this a typical practice when modelling hydrology?

One item that changes in the model is a Link for river elevations -- I suspect that the intent is to model tailwater conditions as the runoff leaves the site into an adjacent river. I am concerned because the only output that I have is the "output summary" which shows an elevation table. Because I am looking at just a summary of output and because I know that links can be used to literally link in entire other portions of a model, could this "river elevations" link contain nodes in another file that might affect the analysis?

Am I correct in assuming that the linked-in river elevations would attenuate any outflow that originates from contributing nodes that have outlets at elevations that are lower than the some of the values in the linked-in river elevations? Because the "river elevations" link does not appear in the 2 year storm model, and then moves location in the models of the other design storms, my suspicion is that the designer may be using the link, whether wittingly or unwittingly, to attenuate the peak and/or total runoff.

Anyone who wants to inspect the Hydrocad output to see how the model changes can view the output here: http://www.davidsonpark.org/drupal/sites/default/files/620/Drainage%20Report/Section%204_HydroCAD%20Worksheets%20-%20Phase%202%20Flow%20to%20Study%20Point%201/Section%204_Phase%202%20Flow%20to%20Study%20Point%201.pdf  and the entire drainage report (watersheds, etc) is here: http://www.davidsonpark.org/drupal/NewDrainage5-14-09. Of course, I have a host of questions, ranging from questions about the model's design (EG: why didn't they model the pumps and infiltration systems when this seems perfectly possible in hydrocad?) to much more specific questions (eg: HSG soil type A doesn't seem reasonable post-development for a very dense, commercial site).  I would be happy to arrange for some kind of consultant arrangement, but keep in mind that we are just a pennyless group of neighbors.


RE: General Questions re output & Link representing river elevations

Many of your questions should be addressed to whoever prepared the report.  There are various reasons for some of the situations you describe, and anyone other than the desinger would just be guessing.  Howevever, a few comments are possible:

Yes, the HydroCAD HCP files are very compact and easy to send by email.  If you want to work with the file yourself just ask the designer.

Although multiple events are generally run within the same file, there can be legitimate reasons for using multiple files.  One case that is suggested by your questions would be event-dependent off-site tailwater conditions, which would need to be specified manually with a link that would be different for each event.  Different modeling scenarios might also be required for certain ponding conditions.  Compare the files and ask the designer about any differences.

Peter Smart
HydroCAD Software

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