BEHAVIOR OF THEORETICAL CURVE NUMBERS WITH RESPECT TO SOIL AND RAINFALL PROPERTIES

Abstract

A dimensional analysis fails to obtain a universal, dimensionless relationshop between the maximum retention potential (S) of the Soil Conservation Service (SCS), runoff curve numbers (CN), and saturated hydraulic conductivity K_s, sorptivity, rainfall parameters, surface runoff, and soil moisture. Next, both S and the theoretical CN (CN_T) were calibrated based on the numerical solutions of Richard’s equation applied to homogeneous soil columns. Result show that S and CN_T are directly related to soil but inversely related to rainfall properties. As a temporally-lumped model, CN generally estimated lower cumulative infiltration than that of Richard’s equation; and in practice, the CN method may perform poorly if (1) Antecedent Moisture Conditions (AMC) is low, (2) the initial rainfall is much higher than K_s which leads to Horton overland florw, or (3) the rain pulses after the initial abstraction is satisfied are small. Before applications, adjustment of CN_T with respect to the standart CN of fallow/idle land to reflect the effect of landuse, land treatment, and hydrologic conditions are recomended.