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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Considerations about the Integration of Deep Unsaturated Zones and Rock Formations into Hydrological Distributed Models of Large Mountainous Catchment Areas"


Determination of the qualitative and quantitative water balance via modelling for a regional water catchment is an indispensable tool for the integrative and sustainable management of water resources in that catchment. The groundwater component of the water balance is often the dominant one and therefore must be properly modelled. The use of deterministic numerical groundwater models performs a large part of this task by computing the flow and transport processes in saturated aquifers and the exchange processes between these aquifers and adjacent surface water bodies. Distributed physical one-dimensional models of the soil zone situated in the first few meters below the ground surface can successfully simulate the infiltration processes in this area, where evapotranspiration in its various forms plays a crucial part. No standard solution, however, is available for the integration in such a hydrological distributed model of deep unsaturated zones and mountainous rock formations, for which much less deterministic information is available. Foreland hilly regions are often characterized by large regional aquifer systems, whose piezometric levels are deep below the ground surface. The in-between zone, often designated as the transfer zone and characterized by a variety of hydrogeological structures, can locally indicate the presence of saturated groundwater bodies with significant horizontal flow, but at the regional scale it must be treated as a quasi-unsaturated area. The fractured and carsted rock formations of the mountainous regions have some factors in common with the transfer zones of the foreland ones. Although very significant hydrological processes take place in them, no traditional deterministic model can be used to describe these processes because of the absence of detailed information regarding their hydrogeological structure, but also of any direct measurements. The available information encompasses physical variables ranging from precipitation and air temperature to groundwater and river water levels, temperature data and results from soil water, saturated groundwater and river models. Starting from it a review is made on the maximum of conclusions one can reach regarding the processes occurring in the transfer and mountainous zones, as well as on the reliability of these conclusions and the best way to make use of them by quantifying the hydrology of these areas. An important aspect of this review is to find methods to calibrate and validate the obtained results, as, again, no direct measurement data is available. The main tools reviewed are regression and correlation analysis methods for the realisation, parameterisation, and regionalisation of conceptual hydrological models. The focus is put on quantifying the quality of the results and on deciding which method is more appropriate under which conditions. Special attention is given to the use of hydrograph analysis methods, as discharge time series at the end of a sub-catchment are the most integrative measure for the hydrological processes occurring inside the sub-catchment. The results of the most significant of the available methods are analyzed and compared, whether event or non-event based, linear, multi-linear, non-linear or purely conceptual. After this, the possibility of putting their results in direct relation to the flow processes in a particular part of the sub-catchment, namely the transfer zone or the rock alpine formations, is studied. If this is even partially the case, an important step forward is made in reaching the goal of completing the hydrological model of the catchment. All the analysis is applied to the Upper Danube catchment (gauge Achleiten near Passau) with a focus on the Ammer catchment (gauge Fischen).