DES 606 Watershed Modeling with HEC-HMS Additional Topics

Additional Topics This briefly covers some advanced features on HEC-HMS These features are not often part of training, but for large production projects are likely to be useful Reference is the User Manual

Analysis HEC-HMS contains some analysis tools that can generate certain statistics from the program with greater ease then exporting results and analyzing externally Documented in Chapter 14 of the user manual.

Multiple Runs Some projects require the analyst to evaluate several different conditions. Page 243 of the user manual mentions setting up multiple runs. Utility is obvious; if change is being evaluated, there is some economy is preparing different scenarios before hand, and just running them in a single execution event.

Other Things HEC-HMS has been illustrated as both a single element calculator and an integrated hydrology quasi-hydraulic modeling tool. Most of the examples required external data preparation Expect this step to be the time consuming activity in modeling, and also the most important.

Other Things Conceptualizing a watershed is important Simple sketches, by-hand, external to the program are advised External calculations are required Esp. for storage-discharge tables, wiers, etc. => This means that diversion and detention models will involve substantial hydraulic considerations before modeling begins

Other Things Sources of design rainfall are available from the internet, TxDOT Hydraulic Manual, etc. Need to document (in a report or notebook) the source of values. The results should be similar, but minor variations that could create arguments, could simply be users choosing different, but authoritative, sources. Cite your data sources.

Other Things Data management Whether data are kept in DSS or in external files is a matter of personal preference in smaller projects (or one-of cases) DSS undoubtedly exists for a good reason; larger projects, or projects that will be shared on a server or by e-mail should probably store all data in DSS and localize the data.

Other Things Supervising a HEC-HMS study. At some point you are likely to supervise a HEC-HMS analysis either as a client, or contractor.

Supervising an HMS Study Agree ahead of time on data sources. If a need arises, agree by consensus Agree that data, even if stored in DSS, have externally readable mirrors maintained by the contractor and delivered with the final product Verify that any files sent to you actually run on the recipient’s machines

Supervising an HMS Study Collectively troubleshoot problematic HEC-HMS runs, there is desirable synergy Carefully isolate calibration runs (I suggest entirely separate project files if at all feasible) Require a modeling report and a simulation log

Supervising an HMS Study Build the model using as few components and special features as practical. Parsimony will go a long way in producing a better modeling study! Don’t subdivide under the illusion of gaining accuracy, probably won’t.

Avoid Use as a Hydraulic Model EM 1110-2-1417

Hydraulics With experience HMS can do some hydraulics quite well, but the data preparation is not trivial. If flow reversal is possible, should use a true hydraulics tool HEC-RAS SWMM

Staying Current HEC-HMS changes from time-to-time. Look and feel will change Icons move about Recommend annual visit to website to check status

Geo-HMS The course entirely ignores the GIS interface of HEC-HMS; however there has been substantial effort in the last two decades to directly integrate HEC-HMS and GIS There is plenty of talent in Texas to help with GIS-HMS integrated modeling, bear in mind that troubleshooting gridded models is hard!

Geo-HMS Most H&H consulting firms can provide guidance Many Universities can provide guidance GeoHMS (and ArcHydro) were written with major contributions from faculty at UT and TAMU