Improved Parameter Estimation Techniques for Soil Storage Capacity
The capacity of surface soil layers to store infiltrated water is a critical factor when simulating runoff response in some natural or developing watersheds. Often, the underlying assumption that is made in hydrologic analyses is that the unsaturated zone is deep enough for unsaturated infiltration to occur throughout the event. However, in some areas this assumption is not valid, particularly for larger storm events. When the soil storage capacity in the unsaturated zone is exceeded, infiltration capacity is reduced or eliminated since capacity can only be regenerated by groundwater flow out of the surficial aquifer or by evapotranspiration (ET). These rates of groundwater flow or ET are often substantially smaller than infiltration rates. Current methods for estimating soil storage capacities are typically based on curve numbers, which use general soil and land use characteristics and most often do not make use of important published soil survey data. This chapter presents a physically based method for estimating the soil storage capacity for specific soil types using data that are readily available in GIS format.
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