DES 606: Watershed Modeling with HEC-HMS Historical Rainfall Theodore G. Cleveland, Ph.D., P.E. 6 OCT 11

Using Historical Rainfall Mechanics of data entry have already been visited in earlier modules –Historical rainfall is generally non-uniform spaced data –DSS utilities exist to help enter such data, but are genuinely difficult to operate. –A viable alternative is to use the historical data to generate a uniformly spaced time series

Rainfall Data Preparation Rainfall data is usually tabulated (either on paper or electronically) with date and time and the associated accumulated rainfall Uniform in-time tabulations are uncommon: –convert a rainfall time-series where the time intervals are varied into uniformly spaced data This derivative time-series can then be used in HEC-HMS as just another time series.

A Procedure Obtain data from source(s) such as: NWS, HCOEM, USGS Convert the date time format into a common unit; for example seconds since start of event. Once data are in common time unit (not date-time), then the analyst can interpolate onto uniformly spaced time units.

Some Details Convert the date time format into a common unit; for example seconds since start of event. –Be aware that gages reset and the analyst may have to manually deal with this issue. –Typically a user-written utility program will take data in the following two-column format and convert it into elapsed time since start of file (i.e. first date-time stamp in the file). –This procedure can be done in Excel, although for large files and/or many files Excel is not an ideal tool.

Some Details Convert the date time format into a common unit; for example seconds since start of event. –Be aware that gages reset and the analyst may have to manually deal with this issue. –Typically a user-written utility program will take data in the following two-column format and convert it into elapsed time since start of file (i.e. first date-time stamp in the file). –This procedure can be done in Excel, although for large files and/or many files Excel is not an ideal tool.

Example Consider the first HMS model presented. –An interpolation approach was presented – in principle, that same spreadsheet can be used

Example Consider a data file such as

Example Some data are every 15 mintes, then to every 30

Example Manual correction is a nuisance

Example Lets modify the file, then pass through a program that fixes time and time steps

Example Copy-Paste into Excel

Example Keep the DATE_TIME and ACC_WTD_PRECIP

Example Add a row to have time start at 00:00 on 5/20/1978

Example Copy-Paste into a Text file for an interpolator program.

Example Open a CMD window. CD to the location of the file Run the program “rain_elapsed_time.exe” Note use of “redirection” program output The data of interest are now in file named “junk.txt”

Example The data of interest are now in file named “junk.txt” Can then put the time and depth into an interpolation spreadsheet

Example Paste back into the junk.txt file and process with “rain_interpolate.exe”

Example Paste back into the junk.txt file and process with “rain_interpolate.exe”

Example Now the series can be put into HMS as just another time series, starting at the user specified date Need to use calculator to determine 2580 minutes is 1 day + 19 hours.

Example Now the series can be put into HMS as just another time series, starting at the user specified date

Example Now the series can be put into HMS as just another time series, starting at the user specified date

Example Now the series can be put into HMS as just another time series, starting at the user specified date

Example Run the model (after changing gages)

Summary Used program to uniformly space time series for HMS use –Could use the Excel sheet for interpolation, but still need the data converted into elapsed time. Alternate approach is to use the R package

Summary Historical storms are time-series entered as gages in HEC-HMS –Data need to be uniformly spaced in time Can experiment with DSSIRIT utility –Prepare data externally to the program Once the derivative time series is built, then remainder is same as other time series.