Delineation of hydrologically similar units in a watershed based on fuzzy classification of soil hydraulic properties

摘要

Evaluation of flow and transport processes in a watershed-scale requires that the watershed be divided into homogenousnspatial units referred to as hydrologically similar units (HSUs). Although a few discretization schemes are already in use,na universally acceptable method of obtaining HSUs is yet to emerge. In this study, we developed a fuzzy inference systemn(FIS) to classify the saturated hydraulic conductivity (Ks) and two water-retention parameters ˛ and n into fuzzy logic-basednsoil hydrologic classes (FSHCs). Analysis of these classes showed that soil properties within an FSHC have less variabilitynand those between two FSHCs have large variability. This result suggested that soils belonging to a specific FSHC may benmore similar than those across different FSHCs and may be grouped together to represent an HSU. Soils within a specificnhydrologic class were aggregated to delineate HSUs within the watershed. For the Dengei Pahad micro-watershed (DPW), thisnapproach showed five distinct regions representing a discretized zone having similar soil hydraulic properties. Application ofnthis approach on a larger international database of soil hydraulic properties revealed that the developed hydrologic classes arenquite comparable across different databases. The delineated HSUs based on these FSHCs were also better than the soil seriesnmap of the watershed in maintaining the soil heterogeneity of the watershed. Moreover, this new discretization scheme usingnthe SWAT modelling environment showed better performance than the soil series-based discretization approach. Copyright n2010 John Wiley & Sons, Ltd.