Which method is appropriate for larger watersheds, typically greater than 200 acres?

The NRCS Curve Number Method is indeed the best choice for larger watersheds, typically over 200 acres, due to its ability to account for various land uses, hydrologic soil types, and cover conditions, which is vital for accurately estimating direct runoff. This method utilizes a curve number (CN) system that correlates land use and hydrologic soil group properties with runoff potential, allowing for more precise predictions in extensive areas.

In larger watersheds, the variability in land cover and soil types can be more pronounced, and the NRCS Curve Number Method can effectively capture this complexity. It is particularly useful for managing agricultural and urban watersheds where different impervious surfaces and soil moisture conditions can influence runoff.

Other methods, such as the SCS Method and the Rational Method, may not be as suitable for larger areas. The Rational Method, for example, is generally limited to smaller watersheds (usually less than 200 acres) due to its straightforward approach, which relies on the peak flow generated from a rainfall intensity that is assumed to occur uniformly over the area. The SCS Method has applications across various watershed sizes, but the NRCS Curve Number Method is specifically tailored for larger areas with diverse characteristics. The Hydraulic Analysis Method, while useful in