WinTR-55 User Manual (NRCS)

Technical Release 55 (TR-55) Urban Hydrology for Small Watersheds was first issued in January 1975 as a simplified procedure to calculate the storm runoff volume, peak rate of discharge, hydrographs and storage volumes required for storm water management structures (SCS, 1975). The first issue involved manual methods and assumed the NRCS Type II rainfall distribution for all calculations.

In June 1986 major revisions were made in TR-55 by adding three rainfall distributions (Type I, IA and III) and programming the computations.  Time of concentration was estimated by splitting the hydraulic flow path into separate flow phases (SCS, 1986).  The computer program became a standard tool to analyze peak flow changes caused by urbanization in many locations.  Its wide acceptance by public and private users has also indicated where improvements could be made in the procedures and the computer program.

A WinTR-55 work group was formed in the spring of 1998 to modernize and revise the Technical Release and the computer software.  The current changes include: upgrade the source code to Visual Basic, change the philosophy of data input, develop a Windows interface and output post-processor, enhance the hydrograph-generation capability of the software and flood route hydrographs through stream reaches and reservoirs.

 

WinTR-55 is a single-event rainfall-runoff small watershed hydrologic model.  The model generates hydrographs from both urban and agricultural areas and at selected points along the stream system. Hydrographs are routed downstream through channels and/or reservoirs.  Multiple sub-areas can be modeled within the watershed.

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.  Up to ten sub-areas and ten reaches may be included in the watershed.

WinTR-55 uses the TR-20 (NRCS, 2002) model for all of the hydrograph procedures: generation, channel routing, storage routing, and addition.

Attachments and Links

USDA NRCS Hydraulics and Hydrology - Tools and Models

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