SCS (NRCS) TR-20 and WinTR-20 Overview
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.
TR-20 simulates the movement of water within a basin by first converting rainfall to runoff using a curve number approach. Next, a direct runoff hydrograph is generated for each subwatershed through the application of unit hydrograph theory. Finally, a Muskingum-Cunge routing is employed to accurately track the movement of water within the stream channel.
Does StormNET support TR-20?
StormNET implements both the
SCS (NRCS) TR-20 and TR-55 methods. A complete description of
StormNET’s TR-20 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.
Click Here for more details about TR-20 and TR-55 modeling in StormNET.
What are the limitations of WinTR-20?
WinTR-20 can only be applied at a watershed scale to basins that meet the following criteria:
Variable |
Limits |
Channel Manning “n” |
.005 – 1.00 |
| Sheet Flow Maximum Length |
100 feet |
| Sheet Flow Manning “n” |
.005 –1.00 |
| Hydrograph Distribution Increment |
>= .01 cfs |
| Runoff Curve Number |
30-100 |
| Weighted Curve Number |
30-100 |
How is the watershed and stream network represented in WinTR-20?
Input for the WinTR-20 model consists of hydrologic and physical parameters that describe the watershed (land and stream system) and the rainfall events being studied. The entire watershed land area should be subdivided into sub-areas. A sub-area is a contiguous relatively homogeneous piece of the watershed where runoff flows to a single point on the stream system. The watershed stream system is subdivided into stream segments called reaches. Reaches are segments of the stream system that represent the configuration of the flow paths in the watershed from other reaches and the sub-area landmasses upstream. Flow from each sub-area can only enter the upstream end of a reach or the watershed outlet. Each stream reach in turn identifies the reach (or possibly the watershed outlet) directly downstream that receives its flows.
What is the minimum set of input parameters for WinTR-20?
The minimum input data set for a WinTR-20 model run includes storm analysis information, a reach (with cross section) and/or sub-area data, and a request for some output. The sub-area data includes area, runoff curve number and time of concentration. If a hydrograph is read in at the head of the reach, sub-area data would not be required.
What type of rainfall or storm analysis information is required for WinTR-20?
A rainfall distribution can be entered or one of several standard rainfall distributions embedded in the program can be used. To define a new rainfall distribution, a unique rain table name (other than the pre-loaded names) must be assigned. Rainfall distributions can be entered in dimensionless form or as actual storm rainfall. Both types are entered as accumulated total rainfall. If the rainfall distribution is dimensionless, the total rainfall amount (depth) for the storm is also entered.
What type of reach data is required for WinTR-20?
Reach data includes an identifier, stream cross section data (elevation, discharge, end area, friction slope, and top width), and channel length. If the valley length is different from the channel length, valley length should be provided as well. A constant base flow value can be added to the reach if appropriate, and split flow can be defined. A reach can also represent an impoundment and its associated storage in the pool area. In this case only a structure rating identifier is needed as reach data.
What sub-area data is required for WinTR-20?
Sub-area data includes an identifier, the drainage area, the runoff curve number (CN), the time of concentration (Tc), and the reach or the watershed outlet receiving the sub-area flow.
What are the required routing parameters in WinTR-20?
The following parameters are required by WinTR-20 in order to perform the channel routing calculations:
- Elevation
- Discharge
- Channel top width
- Friction slope
What type of data can WinTR-20 output?
Output can be requested for each sub-area and each reach individually within the sub-area and reach data sections as well as in the Global Output data section. Output options at the watershed outlet are controlled by the output options selected for sub-areas and reaches in the watershed: if an output is selected at any location in the watershed, it is also provided for the watershed outlet.
What unit systems are supported by WinTR-20?
Entry and output can be in either English or metric units as specified by the user.
Can WinTR-20 calculate the curve number?
If the sub-area curve number is not available, detailed land use and hydrologic soil group (HSG) combination information can be entered for the sub-area. The WinTR-20 model will calculate the curve number.
Can WinTR-20 calculate the time of concentration?
If the time of concentration is not available, detailed flow path information can be provided (flow lengths, slopes, Manning n, and cover type for sheet and shallow concentrated flow and flow length, slope, Manning n, flow end area and wetted perimeter or flow velocity for channel flow), and the program will calculate the sub-area time of concentration.
Does WinTR-20 perform reservoir routing?
The storage indication method is used to route hydrographs through reservoirs.
How is TR-20 different from WinTR-20?
Technical Release 20: Computer Program for Project Formulation Hydrology (TR-20) was released in the 1980’s by the Soil Conservation Service (SCS). In late 1998, a WinTR-20 work group was organized to develop the next generation of the program that would utilize the expanded capabilities of the current computer technologies (windows format). The use of the Muskingum-Cunge approach is also a new addition to WinTR-20. The original MS-DOS TR-20 relied upon a Modified Att-Kin (Attenuation-Kinematic) method for channel routing.
What features of TR-20 are no longer supported by WinTR-20?
The following features from TR-20 that are no longer supported by WinTR-20:
- Capabilities associated with IPEAKS and PEAKS.
- The use of a rain table as a runoff table can be handled by changing affected sub-area CN to 100, which converts all rainfall to runoff.
- A separate Data Check program is no longer needed as data checking is done within the WinTR-20 Controller/Editor model.
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 TR-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.
Can I import TR-20 files into WinTR-20?
The data convert subprogram within WinTR-20 edits and converts most items in the old TR-20 input data sets. However, there are some TR-20 items that are no longer used by WinTR-20. The following will be ignored during conversion:
- Runoff option in the rainfall distribution table
- IPEAKS (intermediate peak output)
- Multiple time increments
Can I import HEC-RAS cross sections into WinTR-20?
Yes. The HEC-RAS reformatter takes a HEC-RAS output file and develops rating tables formatted for WinTR-20 input along with an error file listing any irregularities that would cause WinTR-20 execution problems.
What is contained in the WinTR-20 output files?
The WinTR-20 model has five standard output files: error, debug, printed page output, hydrograph and flood economic. The file extensions are:
- .err for the error file
- .dbg for the debug file
- .hyd for the event file
- .out for the output file
- .ecn for the economic file
Can I interface GIS with WinTR-20?
NRCS Geo-Hydro is an ArcView GIS interface to the WinTR-20 hydrologic model. It operates with ESRI ArcView 3.3 and the Spatial Analyst extension. A complete WinTR-20 hydrologic analysis can be conducted through this interface.
What are some sources of additional information?
The WinTR-20 program, documentation and tutorials can be found on NRCS WinTR-20 webpage. The original TR-20 MS-DOS program and documentation can be downloaded from the NRCS TR-20 webpage. Links to all NRCS hydraulics and hydrologic software can be found here.
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Sources:
Natural
Resources Conservation Service, WinTR-20 User Guide, U. S.
Department of Agriculture, 2006.
Soil Conversation Service (now NRCS), National Engineering
Handbook, Section 4, Hydrology, U. S. Department of Agriculture,
Washington, D. C., 1972.
Soil Conservation Service (now NRCS), TR-20 Computer Program
for Project Formulation Hydrology, U. S. Department of Agriculture,
1992.
Soil Conservation Service (now NRCS), Urban Hydrology for
Small Watersheds, Technical Release 55, U. S. Department of
Agriculture, Washington, D. C., 1986.
