[HEC-USERS] unsteady flow

I'm trying to run an unsteady flow simulation using HECRAS 3.0. I'm starting with a calibrated steady flow simulation and building the unsteady flow files. While I haven't used the unsteady module of HECRAS, I'm quite familiar with SWMM and DAMBRK.

I'd like to input one or more hydrographs from external files for the upstream boundary conditions. The user manual says this can be done with HEC Data Storage System (HEC-DSS) files. What is an HEC-DSS file? Can I create such a file using a spreadsheet? I can't seem to find anything in the electronic manuals about the data format.

Thanks,
Janet Corsale, P.E.
Inter-Fluve, Inc.

Janet - HEC-DSS is a DOS-based hydrologic data base system. You can get the software and manuals from various HEC product vendors, including WRCS, and Dodson, for example, for a nominal amount.

Ford Consulting Engineers also makes available an interface between HECDSS and Windows that might be useful for you.
http://troca.ford-consulting.com/hecdss/.

Good luck.
Ron Kilmartin
ronkilmartin.@attbi.com

Janet

Without knowing the full extent of what you're trying to do, I'd make the following observation.

You could take the time to figure out DSS and have your data available in that format. However, if you are developing the hydrographs externally (ie not in HEC-1 or something that directly writes a DSS file), then in might be simpler to skip DSS altogether.

You could develop your hydrographs externally in Excel and cut and paste them into the appropriate portions of your unsteady flow file. The cut/paste option works quite smoothly. It also gives you the advantage of being sure that you have control over the data, and that the program is seeing exactly the same thing you think its seeing.

David Ford's windows program may make DSS easy to use, and those modelers that have slogged through the up front learning process on DSS may disagree, but I've found DSS to be a bit difficult to use and even more difficult to "control".

Beware there is a considerable learning curve associated with HEC-DSS. So, if you are only running a couple events, do not use Corp software alot, and do not need to exchange information from different corp of engineers programs, then it is probably much simpler for you to avoid HEC-DSS and and cut/paste your boundary condition data directly into HEC-RAS as mentioned by Bill Heatherman.

If you must use HEC-DSS, then get the manuals and download the HEC-DSS software in the default directories in the C drive. Read-up and become familiar with the information in the DSS overview, especially chapters 3 and 4 (they are not long but need to be read well), and the information for the following DSS utility programs: DSSTS (for regular time series data) and DSSITS for (irregular interval time series data or regular time series data at intervals other than those accepted by DSSTS). Pay particular attention to pathname and data conventions.

Then create text files (see below) with your boundary condition input using a spreadsheet.

The DSS manual is a bit cryptic, so once you reach a point of utter frustration with importing your data into HEC-DSS, attach your input text file and carefully describe your DSS input command lines to this listserv and someone should volunteer to bail you out.

text data (stage) formated for input into DSSTS, The start time and regular time interval are given by DOS input commands

.2000
.0660
-.0030
-.0620
-.0560
-.0880
-.1410
-.2160

text data (date, time; stage) formated for input into DSSITS. This data is in the standard 6 minute interval used by USGS and NOAA streamgages. DSS takes 1,2,3,4,5 and 10 minute data intervals but not 6 (can someone explain this?)

13JUL1997, 1924; .2000
13JUL1997, 1936; .0660
13JUL1997, 1948; -.0030
13JUL1997, 2000; -.0620
13JUL1997, 2012; -.0560
13JUL1997, 2024; -.0880
13JUL1997, 2036; -.1410
13JUL1997, 2048; -.2160

If you succeed using DSSTS or DSSITS, might as well learn to use DSPLAY (for viewing your data in tabular and graphical formats) and DSSUTL for manipuilating your data. Then you can swagger like a real HEC-USER.

Janet

The cut/paste feature in HEC-RAS is a little non-standard (and somewhat annoying), in that you have to highlight the entire range you intend to paste into. It doesn't follow the EXCEL convention of assuming you want to fill up all the cells below the point of your cursor. Go into the Flow Hydrograph editor, change the timesteps to 5 min and No of ordinantes to 4977 (as you did), then put your cursor in the box and scroll all the down to the bottom, then hit Ctrl- V and you should have it. (Worked for me just now). Should take about 2 minutes, leaving plenty of time in the New Year for figuring out all sorts of other RAS/UNET quirks ;)

As for the size of the attachment, Gary's point is well taken, but don't take it too hard. Its an easy mistake to make, especially if you don't send things to email servers much, and if your used to the zippy connections most of us in the office setting are blessed with. Welcome to the email group, and keep the questions coming.

One thing you can keep in mind for the future is that the UNET program creates a proliferation of files when it runs that aren't necessary for sending others (or even keeping yourself). Because they all have the same name, and differ only by the appendix, it can be a little difficult to keep track of. In particular, the files with extension "O.." and "R.." are output files that generally don't need to be sent, they can be easily recreated by the recipient. There are several other UNET-specific files that get created on UNET, such as misc Plans you didn't mean to create, DSS and DSC output files that most won't use, "blf" files that are associated with UNET profiles, and couple of others. It takes a little trial and error to figure out whats important and what's not. I've found that HEC-RAS/UNET will generate several MB worth of stuff in the blink of an eye, and frequent file management is a good idea.

Best wishes for the New Year
Bill Heatherman
City of Overland Park, Ks

Would anyone happen to know the limitation for the number of ordinates that HEC-DSS can generate for a hydrograph? I'm interested in generating a simulated long term flow hydrograph that would contain upwards of 300,000 to 500,000 ordinates for input into HEC-RAS as a boundary condition for unsteady flow modelling.

The limitation of 10,000 ordinates by pasting directly into HEC-RAS just doesn't cut it when having to model at a fine time step.

Marc St.Laurent, E.I.T.
mstlaurent@hydro.mb.ca

Marc,

I have a HEC-DSS file with 10-minute data from December 1928 to December 1950. It has 1,156,897 values spread over 8035 records, 6.6 MB. I've used 80 MB files before, too, so I think you're far from a practical limit on the DSS side. However, I've never used that many ordinates within RAS 3.0. If you encounter some limitation there, perhaps you can resample the data to a longer time step with little loss of engineering precision, given the other uncertainties and simplifications behind your 1-D unsteady-flow model, simulated data, and long-term- analysis focus.

Mark Bradshaw