Water dynamics in karst soil: Modelling matrix and preferential flow using reservoir cascade scheme approach

When simulating soil water content (SWC) and dynamics, the reservoir cascade scheme (RCS) approach is considered appropriate in cases when number of parameters for model calibration and validation is limited. This is often the case in Mediterranean karst soils, where due to high rockiness and shallow soil depths it is often difficult to set dense measurement network. In this study, a 1-D model which simulates SWC using RCS approach was developed for a location in central Spain. The soil on the studied site has silt loam texture and is developed on dolomite marbles. The model simulates SWC at daily resolution for six layers in soil that range from 0-50 cm depth, and has three different configurations. Configuration 1 considers only basic RCS module, while configurations 2 and 3 simulate preferential flows in soil as well. Therefore Configuration 2 considers RCS module together with continuous preferential flow module, where between 1 and 5% of available SWC is drained from each soil layer every day. Configuration 3 considers discontinuous preferential flows in addition to two previous modules. Discontinuous preferential flows are active in cases of rainfall events that occur during prolonged dry periods. Simulated SWC values are compared with SWC values measured at five depths in soil, so model parameters are iteratively adjusted to optimize the model results. The simulation produced the best results when implementing Configuration 3: when matrix flow and two kinds of preferential flow are assumed. The model shows that preferential flows could significantly contribute to recharge and should be given more attention in soil hydrological models, especially in karst terrains. It is expected that the model can be implemented in a wide range of locations with karst soils, since it requires limited number of input parameters, but in the same time provides a detailed simulation of soil drainage processes and recharge.