SCS TR55 Method

As mentioned previously, the Soil Conservation Service [16] report on Urban Hydrology for Small Watersheds, known as Technical Release No. 55, provides a simple rainfall/runoff method for peak flow estimates based on the 24 hour net rain depth and the time of concentration t0. This is a graphical approach assuming homogeneous watersheds where the land use and soil type are represented by a single parameter, the runoff curve number (CN). The SCS peak discharge graph shown in Fig. 5 [16] is applied only when the peak flow is designed for 24 hour, type II storm distributions (typical of thunderstorms experienced in all US states except the Pacific Coast ones).

Ug tactor

Figure 3 Lag adjustment factors for Eq. (5) when impervious areas occur in the watershed.

Ug tactor

Figure 3 Lag adjustment factors for Eq. (5) when impervious areas occur in the watershed.

M^flie iMigh moiSad or inipetvkxi» %

Figure 4 Proposed lag factor vs. hydraulic length modified or impervious area (from Ref. 17).

M^flie iMigh moiSad or inipetvkxi» %

Figure 4 Proposed lag factor vs. hydraulic length modified or impervious area (from Ref. 17).

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