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

在SEHAG项目的第二阶段，将使用景观演变模型(LEM)来研究过去、现在和未来泥沙从山坡到渠道、在渠道网络内以及向集水口的侵蚀、输送和沉积。沉积物连通性是一种系统特性，代表了研究区各子系统与泥沙转移的耦合程度。该模型由降水和/或流量数据驱动，并将根据第一阶段生成的1953-2020年期间的许多数字高程模型(DEM)进行校准和评估。虽然DEM of Difference(DEM of Difference，DOD)文件表面只在调查期间发生变化，但该模型将支持对表面变化和泥沙通量的准连续分析。SP8有三个主要目标：(1)继续和深化在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，最重要的是对系统结构(地貌及其形态、土地覆盖)和功能(河道地貌动力学、山坡-河道耦合、产沙量)进行多阶段评估。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“回溯”地貌和地貌地图。与数字高程模型一起，这些地图构成了对地形序列和沉积物瀑布进行图论分析的基础。(2)解释过去和预测未来河流地貌动力学和泥沙迁移的变化。为此，我们使用LEM来显式地模拟河道河段空间尺度上的泥沙侵蚀、输移和沉积。利用超声测深对水库湖泊泥沙总量进行更全面的定量化，将有助于流域出水口产沙量的模型标定。最后，我们利用LEM方法探索了以冲沟和相邻河道下切为特征的坡面过程响应系统。(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LEM输出的连续数字高程模型计算不同空间单元的产沙量与总侵蚀量的比率；它代表功能连通性的度量，并将分析(I)对强迫强度的响应和(Ii)与(静态)连通性指数的比较。形态泥沙平衡的逆方法被用来从国防部计算地貌或更大空间单元之间的泥沙通量。这些结果导致了基于地貌图的区域网络(=加权图)的建立和分析。LEM根据观测到的坡度和河道地貌动力学进行了仔细的校准，最终将被用于解释过去(时间片I-III，1850-2022)和预测未来(2023-2050)的地貌动力学和产沙量。

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.