Water and Solute Fluxes and their Structural Controls at Margins of Floodplain Aquifers

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In typical midland catchments in moderate climate, groundwater flow in floodplains is mainly down-valley oriented. However, the hydrological functioning of floodplain aquifers also depends on the presence or absence of major hydrogeological features, and the local groundwater systems are strongly influenced by water and solute fluxes across their margins. The goal of this project is to elucidate the hydrogeological drivers that determine these fluxes and assess the relative importance of the margins for the overall water balance and solute turnover in floodplain aquifers. The research will be conducted in the Ammer floodplain close to Tübingen (Southwest Germany), which is a typical representative for a mid-section floodplain in moderate climate and has already been studied by the applicants within CRC1253 CAMPOS. To reliably model and predict the hydrological functioning of a floodplain aquifer including its margins, it is essential to know the spatial position, geometry, and hydrogeological properties of water-transmitting structural features at these margins. We will therefore characterize the structural controls at the floodplain margins determining the flux of water and solutes through the floodplain aquifers. In this regard, we aim at labor- and cost-efficient methods to map the spatial extent and geometry of structural features at floodplain margins (using geophysical surveying) and characterize their hydraulic connectivity to the floodplain aquifers (using hydraulic tests). With special focus on the identified structural controls at the floodplain margins, we investigate the water fluxes and corresponding loads of solutes crossing the floodplain margins to quantify their relative contributions within the floodplain aquifer. We will especially investigate the temporal dynamics of the hydrological boundary conditions to identify under which conditions significant water exchange occurs. The experimental findings will inform a consistent numerical model of the floodplain aquifer for predicting signals of hydrogeological measurements and interpreting the results of the estimated dynamic exchange fluxes. Finally, we will compile the geological information gathered in the different investigation steps and in our previous work to perform a comprehensive geological interpretation to identify the guiding geological processes that determine the presence and effectiveness of permeable features at floodplain margins controlling exchange fluxes. This step will facilitate generalizing our findings and transferring it to other sites.