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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 new NRCS-Rain table (added in HydroCAD-10 build 21), provides the latest NRCS rainfall database based on Atlas-14, and uses the new NRCS rainfall distributions including NOAA, NRCC, and MSE, which are gradually replacing the traditional Type I, IA, II and III distributions.  This table will be updated as needed to incorporate new data from state and federal agencies as they continue the full conversion to Atlas-14.

The earlier Atlas-14-Rain table (added in HydroCAD-10 build 14) provides a partial implementation of Atlas-14 data, including updated rainfall depths and some of the newer NRCS rainfall distributions including NOAA_A/B/C/D, NRCC_A/B/C/D, and MSE3/4.  Since this table includes both old and new distributions, you are free to choose the distribution that best suits your modeling objectives and stormwater regulations.  Although this table will continue to be supported for studies that require the initial Atlas-14 data, no future updates are planned.

The original TP-40-Rain table (added in HydroCAD 9.1), uses TP-40 rainfall depths in conjunction with the traditional NRCS Type I, IA, II and III rainfall distributions.  Although this table will continue to be supported for studies that require the older TP-40 rainfall data, no future updates are planned.

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.

How do I use the event lookup tables?

These instructions are based on HydroCAD-10 build 14 or later, which is required in order to use the new Atlas-14 rainfall data the accompanying rainfall distributions.  If you already have HydroCAD-10, make sure you're using build 14 or later (build 21 is preferred).  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.

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

Step 7: (Optional) Click the "View All" button to see all the rainfall events.

Event Viewer

Rainfall Distribution Usage

The following table details the rainfall distributions used for each state in each of the HydroCAD event lookup tables.

  State HydroCAD-9.1
"TP-40-Rain"
HydroCAD 10.0-15
"Atlas-14-Rain"
HydroCAD 10.0-21
"NRCS-Rain"
AK Alaska Type-I Type-I Type I,IA
AL Alabama Type-II,III Type-II,III MSE_4/5/6
AR Arkansas Type-II,III Type-II,III MSE_4/5/6
AZ Arizona Type-II Type-II Type-II
CA California Type-IA,II Type-IA,II CA_1/2/3/4/5
CO Colorado MSE_1/2/3/4/5/6
CT Connecticut Type-II Type-II NRCC_C/D
DC Dist.Columbia Type-II Type-II NRCC_C
DE Delaware Type-II Type II, NOAA_C/D NOAA_C/D
FL Florida Type-III Type-III MSE_4/5/6
GA Georgia Type-II,III Type-II,III MSE_3/4/5/6
HI Hawaii
IA Iowa Type-II Type-II MSE_3/4
ID Idaho
IL Illinois Type-II Type-II Type-II
IN Indiana Type-II NOAA_A/B NOAA_A/B
KS Kansas Type-II Type-II MSE_1/2/3/4/5
KY Kentucky Type-II Type-II, NOAA_A/B/C NOAA_A/B/C
LA Louisiana Type-III Type-III MSE_5/6
MA Massachusetts Type-III Type-III, NRCC_B/C/D NRCC_B/C/D
MD Maryland Type-II Type-II, NOAA_B/C/D NOAA_B/C/D
ME Maine Type-II,III Type-II,III, NRCC_B/C/D NRCC_B/C/D
MI Michigan Type-II Type-II MSE_3/4
MN Minnesota Type-II Type-II, MSE_3 MSE_3
MO Missouri Type-II Type-II Type-II
MS Mississippi Type-II,III Type-II,III Type-II,III
MT Montana
NC North Carolina Type-II,III Type-II,III NOAA_A/B/C/D
ND North Dakota Type-II Type-II Type-I
NE Nebraska Type-II Type-II MSE_2/3
NH New Hampshire Type-II,III Type-II,III, NRCC_A/B/C/D NRCC_A/B/C/D
NJ New Jersey Type-III Type-III, NOAA_C/D NOAA_C/D
NM New Mexico
NV Nevada Type-II Type-II, Nevada_N/S/W Nevada_N/S/W
NY New York Type-II NRCC_A/B/C/D NRCC_A/B/C/D
OH Ohio Type-II NOAA_A NOAA_A
OK Oklahoma Type-II Type-II Type-II
OR Oregon Type-II Type-II Type-II
PA Pennsylvania Type-II NOAA_A/B/C/D NOAA_A/B/C/D
PR Puerto Rico Type-II Type-II
RI Rhode Island Type-III NRCC_C NRCC_C
SC South Carolina Type-II,III Type-II,III NOAA_A/B/C/D
SD South Dakota Type-II Type-II MSE_1/2/3
TN Tennessee Type-II Type-II, NOAA_A/B/C NOAA_A/B/C/D
TX Texas Type-II,III Type-II,III Type-II,III
UT Utah
VA Virginia Type-II Type-II, NOAA_A/B/C/D NOAA_A/B/C/D
VI Virgin Islands Type-II Type-II Type-II
VT Vermont Type-II Type-II, NRCC_A/B/C NRCC_A/B/C
WA Washington
WI Wisconsin Type-II Type-II, MSE_3/4 MSE_3/4
WV West Virginia Type-II Type-II NOAA_A/B/C
WY Wyoming

Rainfall distribution comments

This table summarizes the rainfall distributions used for each state in the latest NRCS-Rain event lookup table.

Distributions States Covered Notes
Type-I,IA,II,III AK IL MO MS ND OK OR TX  
NOAA_A/B/C/D DE IN KY MD NC NJ OH PA SC TN VA WV  
NRCC_A/B/C/D CT DC MA ME NH NY RI VT  
MSE_1/2/3/4/5/6 AL AR CO FL GA IA KS LA MI MN NE SD WI  
Nevada_N/S/W Nevada  

 

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