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HydroCAD® Stormwater Modeling - Since 1986

Sample Rainfall Files

What are the sample rainfall files?

The sample rainfall files are used to demonstrate the different options that are available when creating a custom rainfall distribution by hand.  Choosing the sample file that most closely matches your available rainfall data is generally the easiest way to create a custom rainfall file.  However, most situations do not require a custom file, and are more easily handled using one of the other rainfall setup options.

How do I define a custom rainfall table?

(1) To create a custom rainfall by hand, start by opening the storm distribution report:

On the main menu, select View>Storm Distribution

-or- from the Rainfall tab, select View Storm

This will open the Storm Distribution report as shown at the right.

(2) Scroll down and select the "Sample" storm, which will expand to show the individual sample files.  To display an individual file select it's check-box.  Several files may be selected at once to compare the curves.

(3) Select the file you wish to use as a template and click the Edit button at the bottom of the screen.  In general, use the Sample A file for intensity curves, Sample B file for mass curves, and Sample D for Chicago-style storms.

(4) Enter your rainfall data using the selected sample file.   Before saving your work, be sure to enter a new name from your rainfall, so you don't overwrite the template!  For complete details on rainfall file creation click the Instructions button on the editing screen or see the Rainfall.txt file.

Which sample file should I use?

The following table lists the sample rainfall files that are preinstalled with HydroCAD and discusses the applications for each file. 

Sample file name and comments Actual file contents  (See Rainfall.txt for details)
Sample A - This file defines a 1-hour rainfall distribution using a series of evenly-spaced intensity values.  Time, depth, and intensity units can be changed to suit the available data.  If the storm depth is omitted it is automatically calculated by integrating the intensity data. name=Sample A 1-hr
comment=Intensity curve example

timeunits=hours  (seconds, minutes, or hours)
depthunits=inches  (mm or inches)

duration=1
stormdepth=2.5    (optional - needed only to rescale the entire storm)

inten=0 .20 .60 1.2 2.1 2.15 1.8 1.1 .7 .1 .05
Sample B - This file defines a 1-hour mass curve using evenly-spaced depth values.  By default, HydroCAD applies a smoothing algorithm which produces a smooth intensity curve that avoids "steps" in the runoff hydrograph.  If the storm depth is omitted it is automatically set to the last depth value. name=Sample B 1-hr
comment=Mass curve example w/default smoothing

timeunits=hours  (seconds, minutes, or hours)
depthunits=inches   (mm or inches)

duration=1
stormdepth=2.5  (optional - needed only to rescale the entire storm)

depth= 0 .020 .080 .200 .410 .625 .805 .915 .985 .995 1.000
Sample C - This file is identical to Sample B except that the default smoothing procedure is disabled.  This will produce an exact match to the supplied depth values, but will generate "steps" on the runoff hydrograph due to the constant intensity used between each step. name=Sample C 1-hr
comment=Mass curve example w/o default smoothing
smoothing=false

timeunits=hours  (seconds, minutes, or hours)
depthunits=inches  (mm or inches)

duration=1
stormdepth=2.5    (optional - needed only to rescale the entire storm)

depth= 0 .020 .080 .200 .410 .625 .805 .915 .985 .995 1.000
Sample D - This file defines two rainfall events based on IDF coefficients, often referred to as a "Chicago-style" storm, where the rainfall intensity is defined by the coefficients a, b, and c.
          a                    a
Inten = ------ and Depth = t ------
        (b+t)^c              (b+t)^c

In HydroCAD 10 build 20 or later the b coefficient can be zero.  For earlier versions use a very small b value, such as 0.00001

 name=Sample D 24-hr
comment=Mass curve using IDF Coefficients

timeunits=hours  (seconds, minutes, or hours)
depthunits=inches  (mm or inches)

duration=24
peaktime=12

curve=10-yr
coef1= 0.7035   0.079   0.42

curve=25-yr
coef1= 1.4123   0.065   0.59
Sample E - This file defines a 1-hour rainfall distribution using incremental rainfall depths.  The depth values must be evenly spaced over the specified rainfall duration.  If the total storm depth is omitted HydroCAD will use the sum of all the incremental values.

This format requires HydroCAD 10.0 build 21 or later.

 name=Sample E 1-hr
comment=Incremental rainfall example
smoothing=false

timeunits=hours  (seconds, minutes, or hours)
depthunits=inches  (mm or inches)

duration=1
stormdepth=2.5  (optional - needed only to rescale the entire storm)

incr= .050 .150 .300 .525 .5375 .450 .275 .175 .025 .0125
Sample F - This file defines a 24-hour rainfall distribution using incremental rainfall depths at uneven time steps.  If the total storm depth is omitted HydroCAD will use the sum of all the incremental values.

This format requires HydroCAD 10.1 later.

 name=Sample F 24-hr
comment=Incremental rainfall w/arbitrary time step
smoothing=false
timeunits=hours
depthunits=inches

// The following lines are required only to override
// the inherent duration and depth of the supplied data
// duration=24
// stormdepth=2.5

// first time value sets origin, depth must be zero
timeincr=  0   .00
timeincr=  2   .05
timeincr=  4   .45
timeincr= 10  .52
timeincr= 12  .53
timeincr= 14  .45
timeincr= 16  .27
timeincr= 24  .21
 
Sample G - This file defines a 24-hour rainfall distribution using cumulative rainfall depths at uneven time steps.  If the total storm depth is omitted HydroCAD will use the final rainfall depth.

This format requires HydroCAD 10.1 or later.

 

 name=Sample G 24-hr
comment=Cumulative rainfall w/arbitrary time step
smoothing=false
timeunits=hours
depthunits=inches

/ The following lines are required only to override
// the inherent duration and depth of the supplied data
// duration=24
// stormdepth=2.47

// first time value sets origin, depth must be zero
timedepth=  0   0.00
timedepth=  2   0.05
timedepth=  4   0.50
timedepth= 10  1.02
timedepth= 12  1.54
timedepth= 14  1.99
timedepth= 16  2.26
timedepth= 24  2.47
 

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