This report is commonly known as TR-55. The tables provide estimates of the curve number (CN) as a function of hydrologic soil group (HSG), cover type, treatment, hydrologic condition,...

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

For a more detailed and complete description of land use curve numbers, refer to Chapter Two (2) of the Soil Conservation Service’s Technical Release No. 55 (210-VI-TR-55, Second Ed., June 1986). [1] Composite CNs may be computed for other combinations of open space cover type.

4 Actual curve number is less than 30; use CN = 30 for runoff computations. 5 CN’s shown were computed for areas with 50% woods and 50% grass (pasture) cover. Other combinations of conditions may be computed from the CN’s for woods and pasture.

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 …

Composite CN’s for natural desert landscaping should be computed using figures 2-3 or 2-4 based on the impervious area percentage (CN = 98) and the pervious area CN. The pervious area CN’s are assumed equivalent to desert shrub in poor hydrologic condition.

Number (CN) value is expressed by comparing the features found in the surface of the study area, which are consist of streets, roof, and sub catchments. All the features then being categorized...

1/ Use only one CN source per line. Use CN = . 2. Runoff . (Use P and CN with Table 2-1, Figure 2-1, or equations 2-3 and 2-4.)

** Caution - CN values under 40 may produce erroneous modeling results. NOTE: Site conditions of bare earth or fallow shall be considered as meadow when choosing a CN value for existing undeveloped conditions.

The CN for a watershed can be estimated as a function of land use, soil type, and antecedent watershed moisture, using tables published by the SCS. For convenience, Appendix A of this document...