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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #421879
Research Project: Science and Technologies for Improving Soil and Water Resources in Agricultural Watersheds

Location: Watershed Physical Processes Research

Title: The curve number’s initial abstraction and physical hydrology: ASCE-EWRI CN Hydrology Committee synthesis

Author
item WALTER, TODD - Cornell University
item Bonta, James
item JOHNSON, MICHAEL - Buck Seifert & Jost Inc
item MILLER, JULIANNE - Desert Research Institute
item MINERVINI, WILLIAM - New Jersey Department Of Environmental Protection
item RAMIEREZ-AVILA, JOHN - Mississippi State University
item MOGLEN, GLENN - University Of North Carolina
item NEELAM, TAHNEEN - Cornell University
item OLIVEIRA, PAULO - Federal University Of Mato Grosso
item SHARMA, SURESH - Youngstown State University
item CHIN, DAVID - University Of Miami
item TALCHABHADEL, ROCKY - Jackson State University
item TOLLNER, ERNEST - University Of Georgia
item WARD, TIM - Manhattan College
item WOODWARD, DONALD - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Research Notes
Publication Acceptance Date: 10/29/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: The USDA-NRCS estimates runoff from agricultural and other unmonitored areas for planning and design purposes. A critical underlying parameter in the methodology, called the "initial abstraction" (Ia), represents the amount of rainfall that typically falls prior to the start of runoff from small watersheds. Ia represents the losses of water due to soil-water infiltration and interception by vegetation. Soil-water losses are due to the condition of the landscape surface conditions, whether wet or dry, prior to the rainfall event. Other factors such as rainfall intensity and other storm characteristics also affect Ia. There are many justifiable interpretations of Ia, but there is no single interpretation that applies to all climate and physiographical locations. The paper reviews the various physical interpretations of Ia and documents the need for additional research to remove uncertainties currently found in the application of the methodology.

Technical Abstract: This paper is a technical note discussing various factors and interpretations of a parameter representing the storage of rainfall in soil-water prior to the start of runoff from a watershed. The parameter, denoted the "Ia/S ratio" and "Ia" in the NRCS curve number procedure, is basic to the application of the curve-number procedure by practitioners to estimate total runoff from agricultural watersheds. There are many justifiable physical interpretations of Ia, but there is no single interpretation that appliei to all climatological and physiographical locations. The paper highlights the need for continued research so that the curve-number procedure can be reliably applied to ungauged areas in a variety of climatological and physical conditions.