Does StormNET support TR-55?

StormNET implements both the SCS (NRCS) TR-55 and TR-20 methods. A complete description of StormNET’s TR-55 capabilities can be found here, and a free, fully functional demo can be downloaded from our website. If you would prefer an online, interactive demonstration with one of our engineers please e-mail or call us at 800-488-4775.

How is the watershed and stream network represented in WinTR-55?

A watershed is composed of sub-areas (land areas) and reaches (major flow paths in the watershed). Each sub-area has a hydrograph generated from the land area based on the land and climate characteristics provided. Reaches can be designated as either channel reaches where hydrographs are routed based on physical reach characteristics or as storage reaches where hydrographs are routed through a reservoir based on temporary storage and outlet characteristics. Hydrographs from sub-areas and reaches are combined as needed to accumulate flow as water moves from the upland areas down through the watershed reach network. The accumulation of all runoff from the watershed is represented at the watershed outlet.

What are the limitations of WinTR-55?

WinTR-55 can only be applied at a watershed scale to basins that meet the following criteria:

Variable Limits Minimum area No absolute minimum is included in the software. The user should carefully examine results from sub-areas less than 1 acre. Maximum area 25 square miles (6,500 hectares) Number of Subwatersheds 1-10 Time of concentration for any sub-area 0.1 hour < Tc < 10 hour Number of reaches 0-10 Types of reaches Channel or Structure Reach Routing Muskingum-Cunge Structure Routing Storage-Indication Structure Types Pipe or Weir Structure Trial Sizes 1-3 Rainfall Depth Default or user-defined0 – 50 inches (0-1,270 mm) Rainfall Distributions NRCS Type I, IA, II, III, NM60, NM65, NM70, NM75 or user-defined Rainfall Duration 24-hour Dimensionless Unit Hydrograph Standard peak rate factor 484 or user-defined Antecedent Moisture Condition 2 (average)

What is the minimum set of input parameters for WinTR-55?

While WinTR-55 can be used for watersheds with up to ten sub-areas and up to ten reaches, the simplest run involves only a single sub-area. Data required for a single sub-area run include: identification, dimensionless unit hydrograph, storm data, rainfall distribution and sub-area data. The sub-area data includes area, runoff curve number and time of concentration.

What is the minimum acceptable drainage area for WinTR-55?

The program does not have a drainage area minimum, however, size input should be governed by a minimum time of concentration of 0.1 hours for a single sub-area. Any single sub-area with a drainage area of less than one acre should be carefully checked for reasonable values.

Is there any way to increase the number of sub areas in WinTR-55?

No. The program was developed for small watersheds, so the number of sub areas is limited to 10. For watersheds with more than 10 sub areas, use WinTR-20 software.

Why is WinTR-55 limited to 25 square miles of drainage area?

Modeling watersheds larger than 25 square miles could easily require more than 10 sub areas and possibly require more complex routing than WinTR-55 can provide. Again, WinTR-20 would be a better model for watersheds exceeding this limit.

Is there any way to increase the sheet flow length beyond 100 feet?

No. Sheet flow greater than 100 feet is very unusual in natural watersheds. For more information on the subject read the following document.

Is there a list of hydrologic soil groups in WinTR-55?

No. The previous version of TR-55 had an appendix listing hydrologic soil groups (HSGs) however, HSG information is not hard-coded into WinTR-55 as soil series may be dropped, renamed and reclassified.

Does WinTR-55 have the capability to calculate detention volumes?

WinTR-55 computes detention pond volume for each storm and structure configuration, however, the program no longer estimates the detention volume required. WinTR-55 computes peak flow, storage volume and maximum stage.

What is the recommended procedure for modeling storm sewers in WinTR-55?

WinTR-55 was not specifically designed to model storm sewers. Storm sewers can be modeled as open channels using equivalent trapezoidal channels. It is important to note that this solution will not accurately model pressure flow conditions.

Can StormNET model storm sewers?

Yes, StormNET was designed to model not only overland flow but storm sewers as well. Unlike WinTR-55, StormNET has specific capabilities for pipe networks including pressure flow.

How can I change the time interval of an output hydrograph?

The user has no control over the time increment of the output hydrograph. The time interval is generally 6 percent of the time of concentration.

Are peak discharges calculated using regression equations?

No. The 1986 DOS version of TR-55 used regression equations to determine peak discharges, however, WinTR-55 is actually an input/output interface which runs WinTR-20 in the background to generate, route and add hydrographs.

Will WinTR-55 run old TR-55 DOS based input files?

No. The input file formats are not compatible. The old TR-55 uses tables and graphs out of the 1986 manual in a spreadsheet format. WinTR-55 creates a WinTR-20 input data file and then runs the WinTR-20 computational routine.

Is WinTR-55 related to WinTR-20?

WinTR-55 uses the WinTR-20 model for all of the hydrograph procedures: generation, channel routing, storage routing, and addition.

Should I use WinTR-20 or WinTR-55?

Since TR-55 was originally developed as a simplified version of TR-20, the two methods share several commonalities. The main advantage of WinTR-20 over WinTR-55 is that it can be used on larger, more complex watersheds. WinTR-55 is intended for simple, urban basins that do not exceed 25 square miles with no more than 10 subbasins. These limitations do not apply to WinTR-20.

WinTR-55 assumes a trapezoidal-shaped channel reach and 2-point stage-storage curve for a reservoir. WinTR-20 will accept a channel rating curve and a detailed stage-storage-outflow rating curve. WinTR-55 doesn’t handle diversions, but WinTR-20 does.

What is TR-20?

Technical Release 20 (TR-20) is an event based model for simulating the movement of surface water through a watershed.
TR-20 can be used to analyze current watershed conditions as well as to examine the impact of proposed changes within the watershed. The original theory and verification of the methods used in TR-20 were developed in the 1940’s and 1950’s by the Soil Conservation Service (SCS) in cooperation with the Agricultural Research Service (ARS). Computer code for TR-20 was developed in the 1960’s on mainframes, and the first PC version of the model was released in the 1980’s for MS-DOS. Recently, the Natural Resources Conservation Service (NRCS), formally known as the SCS, released a Windows version of the model called WinTR-20.

What are some sources of additional information?

The original TR-55 documentation and the MS-DOS version can be found on the NRCS TR-55 webpage. The WinTR-55 program, documentation and tutorials can be downloaded from the NRCS WinTR-55 webpage. Links to all NRCS hydraulics and hydrologic software can be found here.