EVENT DETAILS:
Topic: Complacent – Violent Curve Numbers
Date and Time: Friday, May 21, at 12:00PM
Presenters:
Dr. Richard (Pete) Hawkins, University of Arizona, Emeritus
Assisted by Hunter Birckhead PE, Colliers Engineering Design
Cost: Free for NJAFM Members
Length of Presentation: 2 Hours
Continuing Education Credit: 1.0 Credit for the CFM and 1.0 PDH Credit for the NJPE for the one-hour webinar. Continuing Education Credit is available only to those who are current NJAFM members.
Date and Time: Friday, May 21, at 12:00PM
Presenters:
Dr. Richard (Pete) Hawkins, University of Arizona, Emeritus
Assisted by Hunter Birckhead PE, Colliers Engineering Design
Cost: Free for NJAFM Members
Length of Presentation: 2 Hours
Continuing Education Credit: 1.0 Credit for the CFM and 1.0 PDH Credit for the NJPE for the one-hour webinar. Continuing Education Credit is available only to those who are current NJAFM members.
Complacent - Violent Curve Numbers
The Curve Number method was developed in the 1950s by the USDA SCS. and has been used for about 70 years. Because of its popularity, simplicity, and authority it has been used to estimate design runoff from storm events, particularly in determining flood hazard areas. However, since its inception a good deal has been learned about rainfall-runoff hydrology in general, and the CN method and its origins. New applications and developments have emerged and insights have been gained through exercising it.
In 1975, USDA SCS introduced Technical Release 55 entitled, “Urban Hydrology for Small Watersheds”. The land use categories include “Woods or Forest Lands.” In April 1982, a report by Rutgers report determined the Curve Number for “woods” was appropriate for the forested areas in the Pinelands.
In essentially all documents, there is no distinction between “woods” and “forest.” Internally the USDA NRCS regarded woods as farm wood lots or parks, not forest. Accordingly, the user community has assumed the land use category for woods was the same as for forest. In the 1986 version of TR-55 there are limitations noted for forested areas, yet the industry continued on using forest as ‘woods”. It has been used to determine flood hazard areas throughout the State of New Jersey.
In the proposed 2017 rewrite of USDA NRCS Chapter 9 (Hydrologic Soil-Cover Complexes) of NEH4 Part 630 Hydrology, a distinction between woods and forest was made. In particular, the Curve Number method for forest with HSG A soils is not applicable. In fact, under such situations, the rainfall-runoff responses may be classified as Complacent-Violent. Such a scenario was determined from the study at McDonald’s Branch in the New Jersey Pinelands.
The updates and reviews of the Curve Number method found three (3) distinct data clusters in the rainfall-runoff patterns. These are: 1. Standard, 2. Complacent, and 3. Violent. The Standard behavior is the most compatible with the Curve Number model. The Complacent behavior is less common and found in some in some rangelands and forested areas. Violent events are rare (but quite consequential) extreme events springing from Complacent beginnings with large storm and usually pre-wetted in-storm conditions. The CN update recommends that the CN method not be applied to watersheds likely to exhibit Complacent or Violent runoff responses
This webinar will give a brief history of the development of the Curve Number method, the newly found phenomena of Complacent-Violent runoff behavior, and its application to the New Jersey sand pine areas.
In 1975, USDA SCS introduced Technical Release 55 entitled, “Urban Hydrology for Small Watersheds”. The land use categories include “Woods or Forest Lands.” In April 1982, a report by Rutgers report determined the Curve Number for “woods” was appropriate for the forested areas in the Pinelands.
In essentially all documents, there is no distinction between “woods” and “forest.” Internally the USDA NRCS regarded woods as farm wood lots or parks, not forest. Accordingly, the user community has assumed the land use category for woods was the same as for forest. In the 1986 version of TR-55 there are limitations noted for forested areas, yet the industry continued on using forest as ‘woods”. It has been used to determine flood hazard areas throughout the State of New Jersey.
In the proposed 2017 rewrite of USDA NRCS Chapter 9 (Hydrologic Soil-Cover Complexes) of NEH4 Part 630 Hydrology, a distinction between woods and forest was made. In particular, the Curve Number method for forest with HSG A soils is not applicable. In fact, under such situations, the rainfall-runoff responses may be classified as Complacent-Violent. Such a scenario was determined from the study at McDonald’s Branch in the New Jersey Pinelands.
The updates and reviews of the Curve Number method found three (3) distinct data clusters in the rainfall-runoff patterns. These are: 1. Standard, 2. Complacent, and 3. Violent. The Standard behavior is the most compatible with the Curve Number model. The Complacent behavior is less common and found in some in some rangelands and forested areas. Violent events are rare (but quite consequential) extreme events springing from Complacent beginnings with large storm and usually pre-wetted in-storm conditions. The CN update recommends that the CN method not be applied to watersheds likely to exhibit Complacent or Violent runoff responses
This webinar will give a brief history of the development of the Curve Number method, the newly found phenomena of Complacent-Violent runoff behavior, and its application to the New Jersey sand pine areas.
REQUIREMENTS:
Those attending this and future NJAFM webinars who wish to receive a Continuing Education Credit (CEC) for CFM and/or Professional Development Hour (PDH) for NJPE must meet two requirements:
- Active NJAFM Member
- Completion of course evaluation form