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Technical Release 55 (TR-55) presents simplified procedures for estimating runoff and peak discharges in small watersheds. In selecting the appropriate procedure, consider the scope and complexity of the problem, the available data, and the acceptable level of error. While this TR gives special emphasis to urban
Technical Release 55 (TR-55) presents simplified procedures to calculate storm runoff volume, peak rate of discharge, hydrographs, and storage volumes required for floodwater reservoirs. These procedures are applicable in small watersheds, especially urbanizing watersheds, in the United States.
Runoff Hydrograph - TR-55 Tabular Method. The TR-55 Tabular Method approximates TR-20, which is a more detailed hydrograph procedure. This method can develop partial composite runoff hydrographs at any point in a watershed by dividing the watershed into homogeneous subareas.
Hydrograph Method. This chapter presents the Tabular Hydrograph method of computing peak discharges from rural and urban areas, using time of concentration (Tc) and travel time (Tt) from a subarea as inputs. This method approxi-mates TR-20, a more detailed hydrograph procedure (SCS 1983).
Travel time ( Tt ) is the time it takes water to travel from one location to another in a watershed. Tt is a component of time of concentration ( Tc ), which is the time for runoff to travel from the hydraulically most distant point of the watershed to a point of interest within the watershed.
In most cases, the designer will NRCS methods to develop the base use the hydrology (CN, Tc, graphical peak discharge q. p], etc.[), and use that data in one of the numerous hydrologic/hydraulic computer models (including TR-55, TR-20, HEC 1, etc.).
Table 2.1 TR‐55 Manual. What Happens When Adjusted HSGs Are Compared to Non‐Adjusted. These are only hydrologic models, but they show substantial differences from the what is considered “acceptable” engineering practices today. Overall runoff volume increases. Peak flow rates increase. How Much More?
