30th meeting European Working group for Internal Erosion

The 30th meeting of the European Working Group for Internal Erosion (EWG-IE) and the 5th meeting of the European Working group for Overtopping and Erosion (EWG-OOE) were hosted by the University of Bologna in the beginning of September. Below a brief report on the EWG-IE meeting. During this 3-day meeting, the EWG-IE meeting allows for interaction and an international knowledge exchange between experts and practitioners in the field of internal erosion for dams and levees.

Most of the contributions focused on experimental and numerical research related to the internal erosion processes of backward erosion piping and suffusion. The topics ranged from better understanding local mechanisms through local measurements and particle scale models to the application of existing models in practice along some of the main rivers in Europe. Additionally, new research proposals on backward erosion piping and suffusion were presented. Field-scale applications of fibre optics for head measurements and geophysical methods provided inspiration for more advanced data collection. Several participants presented their databases on case histories of breached dams and levees.

Three Dutch contributions were presented on the decision support framework for piping, developed in collaboration with USACE (Vera van Beek and Bryant Robbins), on the KIA ‘piping op veldschaal’  and preliminary experiments (contribution by Joost Pol et al., presented by Vera van Beek), and on research for the application of a SoSEAL barrier as a piping measure (Silvia Bersan).

During the last day of the workshop, we visited the laboratory of the geotechnical department of UvB, where they conduct small- and medium-scale piping experiments to investigate vertical geotextiles as alternatives to more traditional measures. The relevance of internal and external erosion became very clear during the field visit in the afternoon: we visited one of the many sites where a breach occurred during the major floods in the Po area in May 2023. The unprecedented scale of the flooding brings new urgency to the topics of overtopping and erosion. The levees at this site, located in the Emilia region, are currently being reinforced by outward placement and diaphragm walls.

Thanks to Laura Tonni and Michaela Marchi for the organization and warm welcome in Bologna. For more information, please visit https://events.unibo.it/ewg-ie-ooe-meetings-bologna2024.

The next combined meetings will be scheduled on 23-28th of June 2025 in Brno Czech Republic.

Promotion of Mr. Hans van Duivendijk

We congratulate our member of honors Mr. Hans van Duivendijk with his academic promotion.

On 17 June Hans van Duivendijk promoted as oldest promotee ever at Delft Technical University with his work on “Fighting Against the Current”. The dissertation focussed on the kind of easy closure methods used, in the past and at present, to repair breached dikes and to tidal channels by simple means. Hans van Duivendijks promoter was Prof. Bas Jonkman. The study is an unique historical research in the hydraulic engineering field.

Hans van Duivendijk worked whole his career in the field of hydraulic engineering, starting within the company Van Hasselt en de Koning and later Royal Haskoning (nowadays Royal HaskoningDHV). He worked all over the world and focussed on closures of dikes and construction of dams. The photo on the right is from the old box of Hans van Duivendijk where he in 1966 worked at the construction of the Kainji Dam in the Nord of Nigeria.

Beside the civil engineering work and committee work internationally, he worked for 20 years as Associate professor at the TU Delft in the field of hydropower.

Meet Siemen Algra – Master student TU Delft

Hello, my name is Siemen Algra, and I am in the final year of the Master’s program Hydraulic and Offshore Structures at the TU Delft. I’m fascinated by hydropower and large dams, which is why I have chosen this area for my master’s thesis research.

In the Netherlands, not much research is conducted in this area due to a practical reason—the lack of altitude differences in our flat country. This, combined with my love for travel, made me look for opportunities abroad, which is how I ended up in the hydraulic engineering laboratory at the University of Liege. The lab conducts extensive academic research on hydraulic structures, such as dams and hydropower plants, and offers physical modeling services to a wide range of clients, ranging from public administration to private companies in the hydraulics sector.

My research focuses on flow solicitation in plunge pools downstream of free-fall spillways. Spillways are used to evacuate excess inflow discharges from the reservoir to the downstream river. This prevents overtopping at the dam’s crest, which is typically prohibited. Additionally, during extreme events, hydropower plants are often closed, making the spillway the sole route for water evacuation.

Different types of spillways exist; as mentioned earlier my research focuses on the free fall spillway combined with a plunge pool, a configuration used in practice. The free fall is initiated close to the crest of the dam and can take the form of a jet, as seen at the Kariba Dam, or of a nappe—a rectangular, very wide jet—the latter is the primary focus of the research. The nappe, originating from a short free overflow weir, freely falls through the air, potentially dropping up to 100 meters. During this descent, the nappe’s high potential energy transforms into kinetic energy. Due to the interaction between the nappe and the surrounding air, turbulence occurs at the outer edges, causing air to be entrained—making the flow multiphase—and some energy to be dissipated. Then, the high-energy nappe impinges in the plunge pool, where turbulence is again generated due to the velocity gradient between the nappe and the water in the pool. When the plunge ends, the (leftover) nappe impacts on the plunge pool bottom, exerting pressures, which can potentially cause damage.

Being able to predict these pressure characteristics is crucial for designing structures that can withstand them. In practice, this can be done with the use of models. In this research, we use physical scale models. Measurements are taken on these models, and the results are extrapolated to prototype scale. This can be done by using appropriate scale factors or by making the measured parameters dimensionless; i.e. parameters independent of the model’s dimensions, making them directly applicable to prototype scale. However, achieving full similitude between the prototype and scale model is not possible due to the intrinsic nature of gravity driven flows and difficulties with, for example, the scaling of fluid properties and gravity. This introduces so-called scale effects. These scale effects are the results of the inability to achieve full similitude and thus the cause of differences between the conditions on the scale model and the prototype. An example of these scale effects is the huge air-entrainment in prototype flows, resulting in the white-foamy appearance of flow on the prototype, which is more limited on the scale model, as can be seen in the picture below.

Differences shown between a prototype with a fall height of a 100 meters and a scale model of it with a fall height of 1.70-3.00 meters. (Luis G. Castillo, José M. Carrillo & Antonio Blázquez, 2015)

Since, to the best of my knowledge, no prototype data exists to directly assess the influences of scale effects on plunge pool pressures, I will conduct measurements on a model of the same prototype at two different scales to investigate whether and how scale effects influence dimensionless pressure parameters. This study aims to pave the way for developing a scaling relationship. Such a relationship, derived from measurements performed on a variety of scales, would enable predictions on one scale based on measurements done on another. My research would contribute to improve the ability to extrapolate model data and thus to enable better design for better hydraulic structures.

Dam breaches and floods this summer

This summer so far has had several floods and dam breaches, see for example the web links below:

https://www.geoengineer.org/news/days-of-heavy-rain-cause-partial-collapse-of-norwegian-dam

https://www.reuters.com/article/europe-weather-norway-dam/water-breaks-through-flood-gates-at-norway-hydropower-dam-vg-tv-idINL8N39Q5Z2

https://www.thenationalnews.com/world/europe/2023/08/09/norway-could-blow-up-dam-to-stop-it-bursting-after-floods/

https://gazettengr.com/flooding-dam-burst-leads-to-emergency-evacuations-in-eastern-russia/

Fruitful Technical meetings Göthenburg

Last weekend we had fruitful Technical Committee meetings of ICOLD. Members of NethCOLD were joining the Technical Committees of sediment management, embankment dams, dam safety and levees.

Within the levee committee the discussed topics were about safety regulations and its challenges, the use of flood resilience landscapes and the importance of its narratives, partnership between US Army Corps and Rijkwaterstaat, experiences and consequences of major flood event in New Zealand and the completion of the bulletin from the committee with a big effort from Rijkswaterstaat.

In the sediment management the bulletin sediment bypassing is wrapped-up for which the Netherlands gave valued input and support.

Within the embankment dams Committee, for the Netherlands the most remarkable debate was about the use of geotextiles. Despite a vast number of good experiences, several countries reported unexpected issues with clogging or tearing despite good design and workmanship. Cases need to be evaluated to determine what consequence it can have for the common use in the Netherlands.

In the EurCOLD board meeting there was a lot of attention of the role and need of hydropower in the energy transition in Europe, the need of good EU policies and public awareness to strive the goals of this energy transition.