This section outlines different methodologies for modeling ungauged rural catchments. While it is preferable to use a calibrated hydrologic model for water resources studies, especially for rural catchments, this is not always possible. Satisfactory results may still be obtained for macro level studies provided that the modeler chooses the appropriate parameters for each catchment.

The focus of this section is on the Initial Abstraction parameter, IA, and the Time to Peak parameter, TP, parameter. While the CN parameter plays a large role in determining the runoff characteristics of a particular catchment, this parameter can be readily determined and is rarely in dispute by watershed regulating authorities. Guidance is provided in this section on determining the Modified CN parameters, called .