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

在气候温和的典型米德兰集水区，洪泛平原的地下水流主要以向下谷地流动为主。然而，泛滥平原含水层的水文功能还取决于主要水文地质特征的存在或不存在，当地地下水系统受到其边缘的水和溶质通量的强烈影响。该项目的目标是阐明决定这些通量的水文地质驱动因素，并评估边界对泛滥平原含水层的总体水平衡和溶质周转的相对重要性。这项研究将在靠近德国西南部Tübingen的Ammer泛滥平原进行，该平原是气候温和的中段泛滥平原的典型代表，已经由CRC1253 Campos的申请者进行了研究。为了可靠地模拟和预测包括其边缘的泛滥平原含水层的水文功能，必须了解这些边缘的导水构造特征的空间位置、几何形状和水文地质特性。因此，我们将确定泛滥平原边缘的结构控制特征，以确定通过泛滥平原含水层的水和溶质的流量。在这方面，我们的目标是采用节省人力和成本的方法来绘制滩地边缘结构特征的空间范围和几何图形(使用地球物理测量)，并确定其与泛滥平原含水层的水力连通性(使用水力测试)。我们特别关注泛滥平原边缘已识别的构造控制，调查了穿过泛滥平原边缘的水通量和相应的溶质负荷，以量化它们在泛滥平原含水层中的相对贡献。我们将特别研究水文边界条件的时间动态，以确定在哪些条件下发生了显著的水交换。实验结果将提供一个一致的滩地含水层数值模型，用于预测水文地质测量信号和解释估计的动态交换通量的结果。最后，我们将汇编在不同调查步骤和以前工作中收集的地质信息，进行全面的地质解释，以确定决定控制交换通量的泛滥平原边缘是否存在渗透特征及其有效性的指导地质过程。这一步将有助于推广我们的发现并将其转移到其他网站。

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.