USDA NRCS WinTR-55 Small Watershed Hydrology Model

Free NRCS modeling tool for estimating runoff and peak discharge in small watersheds.

WinTR-55 is the standard small-watershed runoff and peak-flow model used in conservation and stormwater planning, available as a free download from NRCS. NRCS also publishes the companion WinTR-20 watershed hydrology system for larger and more complex watershed routing. Both are used widely by engineers, conservation districts, and municipal stormwater programs, and both are useful for watershed groups that want to sanity-check a consultant's numbers or scope a project before hiring one.