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TR-20 vs HEC-HMS

TR-20 vs HEC-HMS

TR-20 vs HEC-HMS

I have been using Win TR-20 by the NRCS for detention pond sizing, flow calculations, etc.  I was lookin on the HEC website and saw HEC-HMS listed as the replacement for HEC-1.  I have not used HEC-HMS, but thought it might be useful to learn it.

Does anyone have any thoughts about the pros and cons of each.  Also, the ability to create interconnected ponds is not present in TR-20.  I have heard IEPA's SWMM has this abilty, and I am trying to determine which program to learn next.

RE: TR-20 vs HEC-HMS

You may wish to check into which programs are acceptable or preffered by the reviewing agencies you will deal with.

RE: TR-20 vs HEC-HMS

SWMM and HEC-HMS are both free, which means that tinkering with them only costs you your time.  I haven't really gotten far into either, but HEC-HMS is more intuitive than SWMM and interfaces with HEC-RAS, whereas SWMM can do water quality calcs.  

RE: TR-20 vs HEC-HMS

I'm looking for similar information on these same two programs. I have been tinkering with swmm and it seems like it could be very useful if I could progress through the learning curve. Once you're out of school its tough to make time to learn relatively complex software.

The only thing i dont like about SWMM so far is how youare forced to put in starting dates and times for the storm events. I don't comprehend this. I just want to put in a model storm event, im not trying to recreate some real event that I have data on. It seems like I have to make up arbitrary dates and times to get the model to run. I don't know if there is a way to 'turn off' this feature or what.

Also, a lot of the water quality stuff seems fairly tightly integrated into the program. I would like it if it was seperated more such that I could 'turn off' all of the water quality features and use it strictly for hydrology/hydraulics and storage design.

I have a lot to learn still, so maybe I will be enlightened on how to get what I want from this program eventaully.

I will download hec-hms as soon as I remember to put in the request to our IT dept...

RE: TR-20 vs HEC-HMS


I don't know what documentation is included with the current SWMM release.  However, when I looked at the SWMM model over 10 years ago, the manual authors took a rather dim view of synthetic storm events vs. historic data (a page is devoted to the problems with synthetic hyetographs).

This may explain the origin of theprogram's desire for starting times.

RE: TR-20 vs HEC-HMS


I think part of this is that SWMM is really more intended as a continuous model and not event driven.  SWMM has some nice pipe features that make the new version (I feel bad you used the old one it was awful) sort of good for urban compared to HEC-HMS.  Also if you ever need to calibrate those really small <5 yr event it is good just because of that continous modeling feature.


I have used both.  HEC-HMS is the much better event model given you have some good hydraulics software to run either your open channel or pipeline calculations.  I use HEC-RAS and Flo-2D mostly so it is my chose, plus I trust the Corps more.
SWMM is really one of the best continuous event models out there.  The other stuff I have seen that seems good are distributed models that you can get from universities or buy expensive (I think WMS is supposed to be good however I can't afford it or the computer to try).

Part of the water quality is that it is an EPA program.  As far as setting dates that is true also in HMS.  I like the feature.  It helps for aligning different hydrographs.  Also it helps sorting models.  I use real dates for actual storms and use a year 3000 January 1 start date for made up events.

RE: TR-20 vs HEC-HMS

at the expense of sounding like an idiot...

How do you obtain real storm data? Is it just a matter of checking rain depth gages and estimating how long the storm lasted? How do you know how the intensity of the storm varied throughout the event?

I would like to model smaller "real" events. usually when we get flooding complaints its during a typical thunderstorm that you get 3 to 5 times per year.

Sorry for asking questions I should probably know the answers to already.  However, I've been doing only geotech work since I got out of school... until now.

RE: TR-20 vs HEC-HMS


A lot raingages have a small cup that tips after some present amount and the number of tips is recorded in time intervals.  You end up with a pretty good record of the hyetograph.

You can get a record from whoever monitors raingages.  You can find NWS data a lot of times or pay for it. I think it can be accessed at:

A lot of local municipalities run at least one gage or have bought the information in the past.

The nice thing for small events is you don't typically have to worry about a very long history for a gage.

RE: TR-20 vs HEC-HMS

in addition to "real" storm data, it is also helpful to have "real" runoff data from the same storm which can help to calibrate your hydrology model

RE: TR-20 vs HEC-HMS

Thanks for your input, I think I will look at HEC HMS next.  I work in Illinois and we have some fairly good regional rainfall data (ISWS Bulletin 70 by Huff and Angel) and ISWS Bulletin 71 for the 6-county Chicago Area.  They have the Illinois broken into several regions and have rainfall data from 5-minute to several day events for the 1-year through about the 500-year event.

I use HEC RAS for my BFE determinations and have traditionally used TR-20 to calculate flows to plug in and it seems to produce flows very similar to HEC-1 when run head to head for the same watershed.

Any thoughts on GEO Ras or Geo HMS???

RE: TR-20 vs HEC-HMS

One advantage of a historical event is that a locality can identify a few real storm events for which they wish to provide protection.  One could pick a typical thunderstorm, and/or a historical event which caused local flooding.  I would imagine folks could identify what these events actually "mean" vs. synthetic return period storms.

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