DES 606
Watershed Modeling with HECHMS
Advanced Topics
Advanced Topics
• This last module before one more set of
exercises and the course examination briefly
covers some additional topics of 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
• Exercise 8 will 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.
– 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
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.
– 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
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.
– Build the model using as few components and
special features as possible.
• 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 Temptation to 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
Stay 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
• 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
– Most consulting firms can also provide guidance