The USDA NRCS Curve Number Method (CN Method) is an application used to provide guidance to design engineers in calculating single event rainfall-runoff volumes that was originally developed in the mid-1950s for agricultural uplands and overland flow. Over time, the CN Method has become entrenched with governmental agencies and private entities dealing with hydrology and embedded in flood control, environmental impact, and sediment-erosion modeling methodologies.
Today, the CN Method has been taken beyond its original intended application and is due for an overhaul to recognize these changes in modern needs as well as the significant additional long-term comprehensive data and analyses that have become available for validation of the Method.
Recognizing the necessity for updating planning and design models for civil engineering and land management purposes, Jeromie Lange, PE, PP, CME, CFM, Senior Principal and Geographic Discipline Leader of Civil and Site services for Maser Consulting P.A. in Red Bank, NJ, recently facilitated the firm co-sponsoring an ASCE seminar entitled “Curve Number Rainfall-Runoff: Professional Application” with The College of New Jersey (TCNJ) and Stevens Institute of Technology.
This seminar addressed the beginnings, strengths, weaknesses and myths of the CN Method and was presented by long-time industry experts Dr. Richard Hawkins of the University of Arizona; Dr. Tim Ward, Dean of Engineering at Manhattan College; and Mr. Don Woodward, former National Hydraulic Engineer for USDA NRCS. All the speakers are part of ASCE Curve Number Method Task Force which is under contract with USDA NRCS to revise NEH4 Part630 Hydrology, Chapters 9, 10, and 11.
The ASCE Curve Number Method Task Force is seeking to raise awareness as to the necessity for modifications to the Curve Number Rainfall-Runoff Method to meet current industry needs and to solicit industry wide participation in the development and peer review of the CN Method updates. If you missed the seminar, the resources below are a good starting point in getting you up-to-speed on this important issue.