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.

为了保护人们，定居点和作为山谷中的经济活动，需要给高山莱茵河的洪水径流和保留水。因此，洪水保护项目“莱茵 - erholung und sicherheit”（“莱茵河 - 娱乐与安全”）或简短若美- 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。

“实现洪水protectio的要求水平n, 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, the required flow section will be created by increasing the river width from currently 60 – 70 m up to several hundred meters in the future. The river channel, which has at present a very technical shape due to diverse river restoration measures during the last 150 years, will by this means retrieve a near-natural state with conditions that mimic the state of the river system before human intervention,”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.

“Two key project sections are replicated consecutively at a scale of 1:50 in extensive hydraulic models. For each section, a flow length of approximately 5 km is replicated (around 110 m in model scale) with watercourse widths ranging from 250 m to 350 m (around 8 m in model scale),”says Hinkelammert-Zens。“同时，创建了项目的数值计算机模型，以提供和评估液压模型的边界条件，以验证结果并进行灵敏度分析。”

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。

From data capture to actionable data

Right: 3D terrain model of a section of the Alpine Rhine (viewed in flow direction) /Left: Movable riverbed in the hydraulic model after the conclusion of an experiment

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 stationto geo-reference the laser scans with 15 reference points. The ScanStation P20 is mounted on a mobile tripod and deployed on four scanning positions to capture the whole model. With a scanning height of approx. 2.7 m - to minimise shadowing effects if viewing angles are too steep and to avoid dead angles – and a resolution of 3 x 3 mm at a radial distance of 10 m to the device, high-quality data with very low noise can be obtained.

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:

• Surface views: The grid values of the scan made at the beginning of the experiment are deducted from those made at the end of the experiment. In this way, theETH teamcreates a view where the relative differences in the height of the model riverbed are visible.

• 横向概要:团队创建交叉的资料es at certain positions, extracting grid values to create lateral profiles. Using the scans before and after the tests, the experts can visualise the observed changes and compare them to the project goals.

• 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：

• Where will gravel banks be positioned?
• 抑郁症将在哪里分解。发生冲突，它们的最大深度将是多少？
• 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.