Protecting the Alpine Rhine Valley from flooding

Author: Renata Barradas Gutiérrez

The Rhine, one of the main rivers in Europe, sources from the Swiss Alps in the canton of Grisons. The Alpine Rhine Valley extends over 90 km along the Rhine from its source in Switzerland via Liechtenstein to Austria. The Valley has a history of devastating flood events that date back to the 11th century. Today, around 300,000 people live in the lower Rhine Valley and numerous companies, including Leica Geosystems, flourish in this area. Due to the intense population and major economic activities in the Rhine Valley, damage potential from major flood events is estimated at EUR 10 billion.

To protect people, settlements, and as economic activities in the Valley, more room for flood runoff and water retention needs to be given to the Alpine Rhine. Therefore, the flood protection project “Rhein – Erholung und Sicherheit” (“Rhine - Recreation and Safety”) – or short若美- 试图将高山莱茵河的流量从3,100立方米/s增加到至少4,300立方米/s，在国际延伸之间，在65公里的65公里处，在支流河Ill和km 91的交界处，阿尔卑斯rhine rhine rhine rhine rhine rhine将其排放到康斯坦斯湖中。该项目成本由奥地利和瑞士同样资助，目前估计为10亿欧元。

“To achieve the requested level of flood protection, the channel geometry of the Alpine Rhine needs to be altered to enhance flood protection along the project perimeter. In the Rhesi project, a very modern approach has been chosen: instead of raising the river’s levees to take account of the elevated discharge of 4,300 m³/s，所需的流程部分将通过将河流宽度从目前的60至70 m增加到将来增加数百米来创建。由于过去150年中各种河流恢复措施，目前的河道河道目前具有非常技术性的形状，它将通过这种情况，以模仿人类干预前模仿河流状态的近天然状态，”瑞士联邦技术研究院（ETH）的液压，水文学和冰川学实验室（VAW）的环境工程师Florian Hinkelammert-Zens解释说。

To evaluate the effects of the projected measures and to check the hydraulic calculations and assumptions of the Rhesi project, VAW of ETH Zurich has been commissioned with hybrid model experiments on behalf of the International Rhine Regulation (IRR) body. These investigations consist of two main parts: 1) experiments in a physical hydraulic model and 2) accompanying numerical simulations.

“在广泛的液压模型中，两个关键项目部分以1:50的比例连续复制。对于每个部分，复制大约5 km的流长（模型尺度约为110 m），水道宽度范围为250 m至350 m（型号尺度约为8 m），”says Hinkelammert-Zens。“At the same time, numerical computer models of the project were created to provide and evaluate the boundary conditions of the hydraulic models, to validate the results and to carry out sensitivity analyses.”

As a result, these two hydraulics models are among the biggest models of alpine rivers ever built, with average dimensions of 110 x 9 m. Both are located in an old factory building in Dornbirn, Austria, where ETH Zurich designed a water circuit with a discharge of 400 l/s. The system consists of a high-level tank, inlet and outlet basins, a water return line in the basement and a deep tank, from which the water is pumped back into the high-level tank (max. 400 l/s).

3D terrain modelling for flood modelling

“在洪水事件中，由于水排放和流速较高，河床会发生重大变化。因此，沉积物可以沉积在多个位置，导致水位上升，也可以侵蚀，例如在桥墩或河岸周围。两种情况都可能是危险的，对防洪产生负面影响。为了复制这些形态学变化，液压模型配备了可移动的河床。”Hinkelammert-Zens说。

为了观察不同的沉积物负荷和各种情况的影响，进行了大量具有不同参数（例如水排出和沉积物负荷）的科学实验。通过激光扫描仪，在每个实验之前和之后都测量模型地形。然后，获得的数据用于创建地形模型，以确定河床中沉积和侵蚀的区域的基础。

从数据捕获到可操作的数据

右：Alpine Rhine的一部分的3D地形模型（在流动方向上查看） /左：实验结束后液压模型中的可移动河床

To capture the topographical data before and after each experiment, the research team of ETH Zurich relies on aLeica ScanStation P20, Leica Geosystems targets and a Leica TS02total station为了地理参考，激光扫描15个参考点。扫描仪P20安装在移动三脚架上，并部署在四个扫描位置上以捕获整个型号。扫描高度约为2.7 m-如果观看角度太陡并避免死角，则最大程度地减少阴影效果 - 在与设备的径向距离为10 m的径向距离下，分辨率为3 x 3 mm，可以获得具有非常低噪声的高质量数据。

每个实验后，数据将导入到Leica Cyclone3D point cloud processing software to register the data and merge the point clouds. At this point, an area of 4000 m²is represented with approximately 250 million points. The point cloud is then ‘trimmed’ using polygons to cut-off the data points outside of the model boundaries. The remaining data points are then transformed into grid cells with a cell size representing 50 cm x 50 cm in real life. Finally, the topographical data is converted into the Swiss National Coordinate System.

Right: visualisation of the observed changes in the riverbed in the hydraulic model after evaluating the laser scan (red: erosion on the outside of the curve, blue: sedimentation on the inside of the curve, viewed in flow direction)/ Left: laser scan in the experiment hall (viewed in flow direction)

“ 3D点云用于创建大约1500万个网格单元的网格数据集，分辨率为0.5 x 0.5 m，每个分辨率为0.5 x 0.5 m，在实验过程中代表一个不同的时间点。然后，在地理信息系统中进一步处理该数据，以创建表面视图以及移动河床的纵向和横向轮廓。这使我们能够在实验的时间内比较不同的点，”explains Hinkelammert-Zens。

The referenced grid dataset can be used in GIS applications for various evaluations, including:

• 表面视图：在实验开始时进行的扫描的网格值是从实验结束时扣除的。这样，ETH teamcreates a view where the relative differences in the height of the model riverbed are visible.

• 横向剖面：团队在某些位置创建交叉配置文件，从而提取网格值以创建侧向剖面。使用测试前后的扫描，专家可以可视化观察到的更改并将其与项目目标进行比较。

• Longitudinal profiles: The extracted cross profiles are averaged for the longitudinal profile. By comparing the averaged riverbed elevations before and after the experiments and by observing the changes in nature, the team of experts can validate the hydraulic model.

Intermediate results and future steps

苏黎世Eth的VAW的调查已经为进一步发展的Rhesi项目提供了重要的投入。首先，通过复制过去的洪水事件对模型进行了校准。在此过程中，将液压模型中获得的水位和河床地形与全面的事件中捕获的数据进行了比较。成功完成此步骤后，液压模型适应了Rhesi预测的河流的未来形状。从那时起，已经模拟了各种长期情景和高洪水事件，以研究Rhesi项目对河流形态和水位的影响。

随着调查仍在进行中，只能引用中间结果。到今天为止，结果表明，瑞典项目的假设和预测是正确的，并且是详细详细阐述未来项目阶段的扎实基础。混合模型实验将持续到2022年夏季，探讨以下技术问题的答案：

• 砾石银行将在哪里定位？
• 哪里萧条职责。搜索发生什么will be their maximum depth?
• How deep must the river banks be protected against erosion and scouring?
• How can bridge piers be secured against erosion and scouring?
• What is the amount of driftwood clocked at bridges during flood events? What will be the effect on the water levels?

The findings of these scientific experiments, supported by reality capture technology from Leica Geosystems, are the basis to ensure sustainable river planning and assure that the Rhesi flood protection project is technically and economically viable. This integrated flood risk management approach will significantly reduce flood risks and improve the ecological and recreational value of the Alpine Rhine in the international stretch.