Using fuzzy approach to build a continuous relationship between SCS curve number and soil properties

The commonly used Soil Conservation Service Curve Number (SCS-CN) for surface runoff modeling is largely dependent on the Hydrologic Soil Groups (HSGs) which are derived through aggregation of all soil types into four hydrologic groups. The derived CN largely mutes away original soil attribute details. A fuzzy approach refining CN according to soil hydrologic properties was developed to preserve difference of CN between different soil types. The proposed approach generally involves three steps: (1) definition of the typical values of soil attributes for each HSG; (2) calculation of the fuzzy membership of a given soil type to each HSG; and (3) calculation of CN for a given soil. Results from a small watershed show that CN from the proposed method effectively retains detailed soil information. The detailed CN derived by the new approach provides possibility for improving distributed hydrologic modeling for many commonly used hydrologic models.