I have seen several reports that refer to a calculation method called the SCS Unit Hydrograph. Is this the same as the Tabular method, or the graphical method as described in the TR-55 manual, both, or something completely different?
I generally associate the unit hydrograph with the TR-55 method of computing flow rates. The typical unit hydrograph is adjusted for the particular conditions (RCN Tc Area etc).
The SCS (now NRCS) Unit Hydrograph is typically used with the SCS runoff procedure, as embodied in TR-20 and other programs. The UH is used to predict the runoff from a single burst of rainfall. Complete runoff hydrographs are produced by combining a large number of UH's for an entire rainfall distribution. (Its actually a bit more complicated, but this is the general outline.) For further info see
The TR-55 Tabular Method is derived from TR-20, and is designed to approximate the runoff hydrographs that would be obtained with TR-20 itself. TR-55 does't use the UH directly, since it is already embodied in the TR-20 results that it employs. For details see
A number of hydrology applications, such as HydroCAD, employ the actual SCS runoff procedure, making it easy to use a different UH if required for special applications. For details see
National Engineering Handbook Section 4-Hydrology, USDA Soil Conservation Service, 1972
This covers the engineering and science behind the unit hydrograph. Type in a search engine and you can download a copy. It is sometime listed as NEH 4