Special Issue on Soil Conservation Service Curve Number (SCS-CN) Methodology

The Soil Conservation Service (SCS) curve number (CN) method is one of the most popular methods for computing the direct surface runoff from a rainstorm. It is popular because it is simple, stable, easy to understand and apply, and accounts for most of the runoff-producing watershed characteristics, such as soil type, land use, hydrologic condition, and antecedent moisture condition. The SCS-CN method was originally developed for small agricultural watersheds and has since been extended and applied to rural, forest, and urban watersheds. Since the inception of the method, it has been applied to a wide range of conditions. In recent years, the method has received much attention in the hydrologic literature.

The SCS-CN method was first published in 1956 in Section 4 of the National Engineering Handbook of the Soil Conservation Service (now called the Natural Resources Conservation Service), U.S. Department of Agriculture. The publication has since been revised several times. However, the contents of the methodology have been nonetheless more or less the same. Being an agency methodology, the method is, in general, accepted in the form in which it exists. Despite several limitations of the method and even questionable credibility at times, it has been in continuous use for the simple reason that it works fairly well at the field level. Recent contributions have significantly enhanced the understanding of the SCS-CN method and consequently, its potential for wider application. In the simplest form, the fundamental proportionality concept of the method relates the two orthogonal hydrological processes of surface water and groundwater, and the other hypothesis relates to the atmospheric process. Qualitatively, the method broadly integrates all three major processes of the hydrologic cycle, and it can thus form one of the fundamental concepts of hydrology.

This special issue of the Journal of Hydrologic Engineering focuses on the SCS-CN methodology and its conventional applications; its advancements incorporating time, rainfall intensity, and infiltration; and its extended applications to areas such as sediment and water quality modeling, base flow and drainage, urban hydrology, coupling with remote sensing, and geomorphologic information system (GIS), besides rainfall-runoff modeling. Within this framework, the papers in this special issue are classified as (1) theoretical and conceptual, (2) conventional applications, (3) advancement, and (4) extended application. The papers entitled “Evolution of the SCS Runoff Curve Number Method and Its Application to Continuous Runoff Simulation,” “Validation of SCS Method for Runoff Estimation,” and “Curve Number Determination Methods and Uncertainty in Hydrologic Soil Groups from Semi-Arid Watershed Data” fall into the theoretical and conceptual category. The papers entitled “Curve Numbers for Nine Mountainous Eastern U.S. Watersheds: Seasonal Variation and Forest Cutting,” “Runoff Curve Numbers for 10 Small Forested Watersheds in the Mountains of the Eastern United States,” “Runoff Modeling in an Agro-Forested Watershed Using Remote Sensing and GIS,” “Spatial Mapping of Runoff from a Watershed Using SCS-CN Method, Remote Sensing, and GIS,” and “RS and Geographical Information System–Based Evaluation of Distributed and Composite Curve Number Techniques,” fall into the conventional application category. The papers entitled “Improved SCS-CN-Inspired Model,” “Improved Storm Duration and Antecedent Moisture Condition Coupled SCS-CN Concept-Based Model,” and “Improved CN-Based Long-Term Hydrologic Simulation Model” belong to the advancement category. The papers entitled “Simulating Turbidity Removal at a River Bank Filtration Site in India Using SCS-CN Approach,” “Estimation of Average Annual Removal Efficiencies of Wet Detention Ponds Using Continuous Simulation,” and “Assessing NEXRAD P3 Data Effects on Streamflow Simulation Using the SWAT Model in an Agricultural Watershed” form a part of the extended application category.

The aim of this issue is to present the state-of-the-art developments/advancements in the SCS-CN methodology and its potential and practical applications in hydrology. The papers included in this issue present substantial evaluation and interesting aspects of the SCS-CN methodology. It is the hope of the guest editors that this special issue will become the first in a sequence of future issues on this topic.