SEHAG - Sediment connectivity, delivery, and the propagation of changes in high Alpine geosystems

在SEHAG项目的第二阶段，将使用一个景观演变模型（LEM）来研究过去、现在和未来的侵蚀、沉积物从山坡到渠道、在渠道网络内以及向集水出口的迁移和沉积。这些沉积物级联，从而传输的变化（集水区的敏感性的一个元素），受到影响的沉积物的连接，系统的属性，代表的程度，研究领域的子系统耦合到沉积物转移。该模型由降水和/或流量数据驱动，并将根据1953-2020年期间第一阶段生成的众多数字高程模型（DEM）进行校准和评估。虽然差分数字高程模型（DoD）仅记录调查期间的地表变化，但该模型将支持对地表变化和沉积物通量的准连续分析。SP 8有三个主要目标：（1）继续和深化第一阶段开始的调查。这包括继续对河道河段进行年度调查，首先是对系统结构（地貌及其配置、土地覆盖）和功能（河道形态动力学、山坡-河道耦合、沉积物产量）进行多期评价。已经在第一阶段，定向和参考的历史照片（特别是时间片I，1850-1920），用于“追溯”地貌和土地覆盖图。这些地图与数字高程模型一起构成了地形序列和沉积级联的图论分析的基础。(2)解释过去和预测未来河流形态动力学和沉积物转移的变化。为此，我们使用LEM明确模拟侵蚀，运输和沉积的泥沙在空间尺度上的通道到达。通过回声测深更全面地量化水库湖泊的总泥沙填充量将有助于模型校准流域出口的产沙量。最后，我们使用LEM探索的过程响应系统的特征是冲沟和邻近河道的下切山坡。(3)对地貌耦合和沉积物连通性采取动态、基于模型的方法。首先，从连续DEM输出的LEM不同的空间单元的泥沙产量总侵蚀的比率进行计算;它代表了功能连接的度量，并将进行分析（一）在响应强迫的大小和（二）在比较（静态）连接指数。形态沉积物预算的逆方法被用来计算来自DoD的地貌或较大空间单元之间的沉积物通量。结果导致建立和分析的区域范围内的网络（=加权图）的基础上的地貌图。LEM，仔细校准观察到的山坡和通道形态动力学，最终将被用来解释过去（时间片I-III，1850-2022年），并预测未来（2023-2050年）的形态动力学和产沙量。

In the second phase of the SEHAG project, a landscape evolution model (LEM) will be used to study past, present and future erosion, transport and deposition of sediments from hillslopes to channels, within the channel network, and towards the catchment outlet. These sediment cascades, and thus the transmission of changes (an element of catchment sensitivity), are influenced by sediment connectivity, a system property that represents the degree to which subsystems of the study areas are coupled with respect to sediment transfer. The model is driven by precipitation and/or discharge data and will be calibrated and evaluated against numerous digital elevation models (DEMs) generated in phase one for the period 1953-2020. While DEMs of difference (DoD) document surface changes only for inter-survey periods, the model will support a quasi-continuous analysis of surface changes and sediment fluxes.SP8 has three main objectives: (1) To continue and deepen the investigations started in phase one. This includes the continuation of annual surveys of channel reaches, and above all the multitemporal evaluation of system structure (landforms and their configuration, landcover) and functioning (channel morphodynamics, hillslope-channel coupling, sediment yield). Already in phase one, oriented and referenced historical photos (esp. time slice I, 1850-1920), are used for “back-dating" geomorphological and landcover maps. Together with DEMs, these maps form the basis for a graph-theoretic analysis of toposequences and sediment cascades. (2) To explain past and to project future changes in fluvial morphodynamics and sediment transfer. To this end, we use the LEM to explicitly model erosion, transport and deposition of sediment at the spatial scale of channel reaches. A more comprehensive quantification of total sediment infill of reservoir lakes by echosounding will aid model calibration on sediment yield at the catchment outlet. Finally, we use the LEM to explore the process-response system of hillslopes characterized by gullying and undercutting by adjacent river channels. (3) To take a dynamic, model-based approach on geomorphic coupling and sediment connectivity. First, the ratio of sediment yield to gross erosion is calculated for different spatial units from sequential DEMs output by the LEM; it represents a metric of functional connectivity and will be analysed (i) in response to forcing magnitude and (ii) in comparison to (static) connectivity indices. The inverse approach to morphological sediment budgeting is used to compute sediment fluxes between landforms or larger spatial units from DoD. The results lead to the set-up and analysis of area-wide networks (=weighted graphs) based on the geomorphological maps. The LEM, carefully calibrated on observed hillslope and channel morphodynamics, will finally be employed to explain past (time slices I-III, 1850-2022) and to project future (2023-2050) morphodynamics and sediment yield.