Protecting the Alpine Rhine Valley from flooding

作者：Renata BarradasGutiérrez

莱茵河是欧洲的主要河流之一，来自格里斯森广州瑞士阿尔卑斯山的来源。高山莱茵河谷（Alpine Rhine Valley）沿着莱茵河（Rhine）从瑞士的来源延伸到90公里，并通过列支敦士登（Liechtenstein）到奥地利。山谷有毁灭性洪水事件的历史，可以追溯到11世纪。如今，大约30万人居住在莱茵河下部和许多公司，包括Leica Geosystems，在该地区蓬勃发展。由于莱茵河谷的强烈人口和重大经济活动，重大洪水事件的破坏潜力估计为100亿欧元。

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Rhesi- seeks to increase the flow capacity of the Alpine Rhine from 3,100 m³/s to at least 4,300 m³/s on the international stretch between kilometre 65 at the junction of the tributary river Ill and km 91, where the Alpine Rhine discharges into Lake Constance. The project costs, funded equally by Austria and Switzerland, are currently estimated at EUR 1 billion.

“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, 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,”explains Florian Hinkelammert-Zens, environmental engineer at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) at the Swiss Federal Institute of Technology Zurich (ETH).

为了评估预计措施的效果，并检查了恒河部项目的液压计算和假设，苏黎世Eth的VAW已代表国际莱茵河调节（IRR）机构进行了混合模型实验。这些研究由两个主要部分组成：1）在物理液压模型中进行实验和2）伴随的数值模拟。

“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),”Hinkelammert-Zens说。“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。”

结果，这两种液压模型是有史以来最大的高山河流模型之一，平均尺寸为110 x 9 m。两者都位于奥地利Dornbirn的一栋古老的工厂建筑中，苏黎世Eth设计了一个排放400 l/s的水路。该系统由一个高级水箱，入口和出口盆地，地下室中的水流线和一个深水箱组成，从中，水从中泵回高级水箱（最多400 L/s）。

3D terrain modelling for flood modelling

“During a flood event, a riverbed is subject to significant changes due to high water discharges and flow velocities. Hence, sediment can be deposited at several locations, leading to rising water levels, or can be eroded, e.g. around bridge piers or along the river banks. Both scenarios can be dangerous and have a negative effect on flood protection. To replicate these morphological changes, the hydraulic models are equipped with movable riverbeds.” says Hinkelammert-Zens.

To observe the impact of different sediment loads and various scenarios, a large number of scientific experiments with varying parameters (e.g. water discharge and sediment load) are conducted. By means of a laser scanner, the model topography is measured before and after every single experiment. The acquired data is then used to create terrain models which serve as a basis for the determination of areas where sedimentation and erosion occur in the riverbed.

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 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。

After each experiment, the data is imported into狮子旋风3D 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.

右：评估激光扫描后，液压模型中观察到的变化的可视化（红色：曲线外部侵蚀，蓝色：曲线内部的沉积物，在流动方向上观察）/左：激光扫描在实验大厅（以流向查看）

“The 3D point clouds are used to create grid datasets with approximately 15 million grid cells with a resolution of 0.5 x 0.5 m, each of them representing one distinct point of time during the experiments. This data is then further processed in geo-information systems in order to create surface views as well as longitudinal and lateral profiles of the mobile riverbed. This enables us to compare different points in time of the experiment with each other,”explains Hinkelammert-Zens。

引用的网格数据集可以在GIS应用程序中用于各种评估，包括：

• 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.

• Transverse profiles: The team creates cross profiles 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.

中级结果和未来步骤

The investigations by VAW of ETH Zurich already led to significant inputs for the further development of the Rhesi project. At first, the model was calibrated via the replication of past flood events. During this process, the water levels and riverbed topography obtained in the hydraulic model were compared to data captured during those events in full-scale. After successful completion of this step, the hydraulic model was adapted to the future shape of the river, as projected in Rhesi. Since then, various long-term scenarios and high flood events have been simulated to investigate the effects of the Rhesi project on the river morphology and water levels.

As the investigations are still ongoing, only intermediate results can be cited. Up to today, the results show that the assumptions and projections of the Rhesi project were correct and are a solid basis for the elaboration of future project stages with greater detail. The hybrid model experiments will continue until summer 2022, exploring answers to the following technical questions:

• 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？
• 米多深ust the river banks be protected against erosion and scouring?
• 如何保护桥梁免受侵蚀和冲洗的侵害？
• 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.