Author : Samakkee Boonyawat

Summary : A watershed class prediction equation in Thailand was proposed by Wooldridge (1984). The equation is a multiple linear regression which was developed using five variables, i.e., slope, elevation, landform, soil and geology without any transformation. Theory, however, suggests that the relationship between watershed class and the explanatory variables is not linear and the original equation requires too many variables. Therefore, linearized models were developed using one to five explanatory variables. An analysis of the different equations tested showed that the equation using logarithmic transformation at the right side of the equation was the most appropriate form. Therefore, this form of the equation was used to develop the equations to predict watershed classes for the three rock type watersheds. Watershed class prediction equations for all rock types taken together and each rock type considered individually, namely : granite, sandstone and limestone were developed from 300 randomly selected grids of each rock type of northern Thailand.