Utveckling av en HBV/PULS-model med sammanfogade markfuktighets- och responsrutiner
Soil properties affect the chemical composition of soil water. When studying transport of chemical substances through a basin, it is therefore important to know from which soil layer the main part of the runoff is generated. The aim of this study is to develop an HBV/PULSE model with merged soil moisture and response routines, which generates good approximations of groundwater levels. It should be possible to extend the model to simulate transport of substances and take into account which soil layer the groundwater level is currently in. The hydrological version of HBV/PULSE is used since there is no need to account for pH or alcalinity at this stage. Representation of runoff is changed to an equation analogous to that of HBV-96. The unsaturated and saturated zones in the response routines are merged by associating change in groundwater storage with change in the size of the unsaturated zone. Field capacity, which is expressed in mm in the existing model, is transformed from parameter to variable. Three models are compared in this study: HBV/PULSE without any modifications, HBV/PULSE with a response function similar to that of HBV-96 and finally a model with the same response function as model two, variable field capacity, groundwater level simulation and connected soil moisture and response compartments. Results show that runoff is simulated equally well by the two first model versions, and alomst as well by the third. Soil moisture simulations show the same patterns for all three models, but slightly different levels. Ground water storage is different in the first model compared to the others, mainly depending on the use of capillary flux andnegative storage values in the unmodified model. Groundwater simulations with the third model generated results which differed much from measurements. The main problem is the magnitude of the variations which is far too small in the simulations. Introduction of variable soil moisture in the unsaturated zone and variable soil porosity is suggested as a way of increasing the magnitude of fluctuations in groundwater storage and levels. It is also necessary to allow groundwater storage, and thereby groundwater levels, to vary equally in both directions from the initial values. If this is not possible to achieve with the new response function, it is necessary to change back to the old function despite the increase in parameters.