Dynamic Curve Numbers

Abstract

In this chapter, after giving an introduction on the CN method and the factors affecting the CN value, the advantages and disadvantages of the method have been discussed. A review of different literature defines that among different factors that affect the CN value, hydrologic soil groups and land use/cover are the most effective factors and the CN value is mainly determined by these two factors. The CN method has been widely used around the world due to its simplicity and dependency of the method on only one parameter: CN. However, it has some weak points such as that time is ignored in the method, moisture soil condition and subsequently the relation between the initial abstraction and maximum retention probability of the soil is ambiguous, and, finally, the effects of temporal and spatial variability of the hydrologic condition are not considered in the original method. The stated problems in the method can cause a huge error in the estimation process. Hence, in this chapter, two main different types of modifications to solve the real weak points of the method were reviewed.