Prev Topic Home Up Next Topic

HydroCAD Stormwater Modeling - Since 1986

Event Lookup Tables

Why use the event lookup tables?

Event Lookup TableThe event lookup tables are the easiest way to define the rainfall events in a HydroCAD project.  After selecting your project location (typically by county), the lookup table defines the rainfall distribution and rainfall depth for each return period.  This allows HydroCAD to automatically create a set of rainfall events for the current project.

What lookup tables are provided with HydroCAD?

The first event lookup table was implemented in HydroCAD 9.1, and used TP-40 rainfall depths in conjunction with the traditional NRCS Type I, IA, II and III rainfall distributions.  Originally distributed as NRCS-Rain, this table has been renamed to TP-40-Rain to better identify its contents.

In HydroCAD-10 build 14, a second lookup table was added based on the latest Atlas-14 data.  In addition to providing updated rainfall depths, the new Atlas-14-Rain table also references the latest NRCS rainfall distributions (e.g. NOAA_A/B/C/D, NRCC_A/B/C/D, and MSE3/4) which are gradually replacing the traditional Type I, IA, II and III distributions.  Since the table includes both old and new distributions, you are free to choose the distribution that best suits your modeling objectives and stormwater regulations.

How do I use the event lookup tables?

These instructions are based on the latest HydroCAD-10 build 14, which is required in order to use the new Atlas-14 lookup table and the accompanying rainfall distributions.  If you already have HydroCAD-10, make sure you're using build 14 or later.  Users of earlier versions must update to HydroCAD-10 to use the new lookup tables.

Step 1: Open the Settings|Calculation screen, select the Rainfall tab, and click "Load Events from...Lookup Table".  This will open the event lookup screen shown at the top of this page.

Step 2: Select the desired "Event Lookup File" from the drop-down list.

Step 3: Select your state from the drop-down list, or manually scroll down to your state.

Step 4: Select (click) the line for your specific county and click OK.  HydroCAD will display an event confirmation box.

Step 5: If more than one Storm Distribution is available for your location, select the desired distribution for your project.  If you need help selecting the correct distribution, consult your stormwater regulations or see the state-specific guidance below.

Event ViewerStep 6: Click OK to create the rainfall events for the current project.

Tip: You can review your event settings at any time by clicking the "View All" button on the Rainfall tab.

Lookup table details

The TP-40 lookup table is based primarily on data from the NRCS WinTR-55 program, with corrections made for rainfall distributions and other anomalies.  Although this table will continue to be supported for studies that require the older TP-40 rainfall data, future updates will be minimal.

The new Atlas-14 lookup table represents a compilation of data from the latest release of WinTR-55 and many other sources.  It will be updated as needed to incorporate new data from state and federal agencies as they continue the full conversion to Atlas-14.  Although rainfall depths have generally been updated to Atlas-14, many states have not yet developed new Atlas-14 rainfall distributions, and continue to use the older Type I, IA, II, and III distributions.  Please see the table below for details on rainfall distributions for specific states.

Remember: In addition to the lookup tables and predefined rainfall distributions, HydroCAD also gives you the option to download site-specific data and generate a custom rainfall distribution.  This option can be used for localities that haven't developed new rainfall distributions, or for improved accuracy over the county-level rainfall data.

Details for lookup table "Atlas-14-Rain"

  State Old Type(s) New Type(s) Comments (see notes, below)
AK Alaska I   New distributions pending
AL Alabama II,III   MSE distributions pending
AR Arkansas II,III   MSE distributions pending
AZ Arizona II   New distributions pending
CA California IA,II   Update pending
CO Colorado     Update pending
CT Connecticut II   NRCC distributions pending
DC Dist.Columbia II   NOAA distributions pending
DE Delaware II NOAA_C/D Updated in build 15
FL Florida III   MSE distributions pending
GA Georgia II,III   MSE distributions pending
HI Hawaii     Update pending
IA Iowa II   MSE distributions pending
ID Idaho     Update pending
IL Illinois II   New distributions pending
IN Indiana II NOAA_A/B Updated in build 15
KS Kansas II   MSE distributions pending
KY Kentucky II NOAA_A/B/C Updated in build 15
LA Louisiana III   MSE distributions pending
MA Massachusetts III NRCC_B/C/D Updated in build 15
MD Maryland II NOAA_B/C/D Updated in build 15
ME Maine II,III NRCC_B/C/D Updated in build 15
MI Michigan II   MSE distributions pending
MN Minnesota II MSE_3 Updated in build 15
MO Missouri II   MSE distributions pending
MS Mississippi II,III   MSE distributions pending
MT Montana     Update pending
NC North Carolina II,III   NOAA distributions pending
ND North Dakota II   MSE distributions pending
NE Nebraska II   MSE distributions pending
NH New Hampshire II,III NRCC_A/B/C/D Updated in build 15
NJ New Jersey III NOAA_C/D Updated in build 15
NM New Mexico     Update pending
NV Nevada II Nevada_N/S/W Updated in build 15
NY New York II NRCC_A/B/C/D Download NOAA data for compatibility with "N10" rainfalls used in EFH-2 software
OH Ohio II NOAA_A Updated in build 15
OK Oklahoma II   MSE distributions pending
OR Oregon II   Update pending
PA Pennsylvania II NOAA_A/B/C/D Updated in build 15
PR Puerto Rico II   New distributions pending
RI Rhode Island III NRCC_C Updated in build 15
SC South Carolina II,III   NOAA distributions pending
SD South Dakota II   MSE distributions pending
TN Tennessee II NOAA_A/B/C Most counties updated in build 15
TX Texas II,III   New distributions pending
UT Utah     Update pending
VA Virginia II NOAA_A/B/C/D Updated in build 15
VI Virgin Islands II   New distributions pending
VT Vermont II NRCC_A/B/C Updated in build 15
WA Washington     Update pending
WI Wisconsin II MSE_3/4 Updated in build 15
WV West Virginia II   NOAA distributions pending
WY Wyoming     Update pending

Rainfall distribution comments

This table summarizes the new Atlas-14 rainfall distributions being developed by the NRCS.
New Distributions Planned Covered Notes
NOAA_A/B/C/D DC DE IN KY MD NC NJ OH PA SC TN VA WV Details pending for DC, NC, SC, and WV.
NRCC_A/B/C/D CT MA ME NH NY RI VT Details pending for Connecticut.
MSE_1/2/3/4/5/6 AL AR CO FL GA IA KS LA MI MN MO MS NE ND OK SD WI MN and WI updated to build 15, others in build 21.
Nevada_North/South/West Nevada Update complete.


[Home]   [Support] 
Copyright 2015 HydroCAD Software Solutions LLC (privacy)   (legal notices)