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1. Topics of interest were defined following a risk based approach. 2. Study priorities were set based on knowledge gaps in current practices, but they were conditioned by pragmatic limitations. 3. Focus topics : failure modes, detection and monitoring and repairs. 4. Serious failures can occur in sections with large burrows (e.g. fox and beaver holes), but also in sections with mole burrows. Research in progress. 5. Detection and monitoring techniques were developed and tested in the living lab, but results are site specific. Further testing is needed for benchmarking. 6. A low cost repair technique was developed and evaluated.
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Infosheet. Within the context of animal burrows surveys that took place in the test season 2021-2022 in the living lab Hedwige-Prosperpolder, an experimental setup with smoke bombs was developed to verify whether detected burrows by small rodents are interconnected in the subsurface. By injecting colored smoke in one of the detected burrows the team could observe if the smoke would exit the ground from other burrows in the proximity gaining insight into the extent of subsurface connections of burrows. The detection of several exit points is a sign that there is a system of tunnels in the levee that leads to a den. This is most likely a weak spot on the levee that requires attention by the levee managers. The test was repeated 5 times using different variants in its assembly and also testing burrows by larger animals. This helped to gradually improve the setup and make it more practical for use by levee inspectors.
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Infosheet. When high water is expected, levee managers need to make sure that there are no weak spots on the levee that can compromise its structural integrity. Animal burrows on a section can constitute weak spots that have to be urgently repaired in anticipation of high water. Within the context of overflow experiments, a temporary protection with road plates was installed on a section where mole burrows had been previously detected, and where the presence of an extensive subsurface system of mole tunnels had been verified. The set-up was subsequently tested against overflow.
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Animal burrows create discontinuities on the body of earthen levees that under certain circumstances can threaten their structural integrity through hydraulic alteration and surface erosion. Although it is a virtually established fact that discontinuities can undermine the structural integrity of levees, there are limited studies that clarify when animal activity can be considered dangerous and which are the most effective approaches for dealing with it. Interaction with levee management agencies in the network of Polder2C’s has shown that there is much tacit knowledge on the topic among levee guards in the Netherlands, Belgium, France and the UK, which has only been marginally reported so far. It is also of interest that the Dutch Government approved the inclusion of measures against harmful animal activity in flood defences more than a decade ago (Tweede Kamer 2010), but to this end, an integrated national management framework is still pending. This highlights the fact that formal knowledge on the topic is limited and fragmented. In order to enable the development of a rational framework for dealing with animal activity on levees, a coordinated effort is required for the review and reporting of existing knowledge, identification of knowledge gaps and development of approaches to determine the level of risk incurred by various types of animal activities on levees and the effectiveness of reduction actions. This report presents activities that took place within Polder2C’s and could support the development of such a rational framework. After the first winter of experimentation in the Living Lab Hedwige-Prosperpolder, evidence was produced about possible adverse impact of animal- and vegetation-induced discontinuities on levees (Holscher & Zomer, 2021; Koelewijn et al. 2021). Overflow experiments at locations of anomalies caused by grazing sheep, trees and fox holes led to severe erosion of the structure within a considerably short time (see also Figure 1.2a). In June 2021 a mole burrow system was detected in a levee section that had been damaged during overflow experiments and where an emergency repair application with rock bags had been subsequently applied. In order to explore the geometry and extent of the system, the mole tunnels were grouted with fast drying concrete. Upon excavation of the concrete an extensive burrow system was revealed with exit points close to the toe and close to the crest of the section (see also b). In preparation of the second winter of experimentation, a cross-work package team was created to identify knowledge gaps in the management of animal burrows on levees and suggest research activities that could potentially fill in identified gaps. This led to a longlist of possible activities, a number of which were eventually executed in the period September 2021 till February 2022. The final selection of activities was limited by the contractor’s work and other large-scale experiments and exercises. Priority was given to activities that had no conflicts with the abovementioned operations and for which there was available equipment and manpower within the involved organizations. This report presents the work that was performed within Polder2C’s on the management of harmful animal activity on levees in a chronological order. It starts with a description of observations in the first year of the project, and a subsequent study that led to the development of a knowledge agenda in the period February till June 2021. It continues with a description of activities that took place in a more coordinated manner in the second year of the project and it ends with a summary of key findings.
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Engineers design levees without taking into account animal activity. But in reality: *Levees attract burrowing animals *Many of them are protected (e.g. beavers) *It is not always easy to detect burrows and remove them Topics of interest are: 1. Eco engineering approaches for deterrence of animals How can we make animals go elsewhere? 2. Detection and measurement techniques How can we find burrows on a levee and measure their geometry? 3. Failure paths How do levees fail when they have burrows? 4. Effectiveness of countermeasures How can we repair levee damages made by burrowing animal?s
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Poster. During Polder 2 C’s a winter school and a late summer school were organized to accelerate dissemination of knowledge used and developed within the project to the next generation of flood protection professionals.
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Kring of Coastal Engineers workshop, Rotterdam 25 September 2022
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Implementation of reliable methodologies allowing Reduction, Refinement, and Replacement (3Rs) of animal testing is a process that takes several decades and is still not complete. Reliable methods are essential for regulatory hazard assessment of chemicals where differences in test protocol can influence the test outcomes and thus affect the confidence in the predictive value of the organisms used as an alternative for mammals. Although test guidelines are common for mammalian studies, they are scarce for non-vertebrate organisms that would allow for the 3Rs of animal testing. Here, we present a set of 30 reporting criteria as the basis for such a guideline for Developmental and Reproductive Toxicology (DART) testing in the nematode Caenorhabditis elegans. Small organisms like C. elegans are upcoming in new approach methodologies for hazard assessment; thus, reliable and robust test protocols are urgently needed. A literature assessment of the fulfilment of the reporting criteria demonstrates that although studies describe methodological details, essential information such as compound purity and lot/batch number or type of container is often not reported. The formulated set of reporting criteria for C. elegans testing can be used by (i) researchers to describe essential experimental details (ii) data scientists that aggregate information to assess data quality and include data in aggregated databases (iii) regulators to assess study data for inclusion in regulatory hazard assessment of chemicals.
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Report on testing of water overflow on Dutch levees. On the Dutch part of the levee in Hedwige-Prosperpolder, 11 overflow tests have been conducted. Overflow tests on levees are designed to test the strength of levees and levee covers under the load of a continuously overflowing discharge of water. For this purpose, Flanders Hydraulics Research have designed and built an Overflow Generator (Vercruysse et al., 2022) within the framework of the Polder2C’s project. This device allows to generate a controlled and homogenous discharge of water over the levee crest. Within the Polder2C’s project, 27 overflow tests on 11 Belgian and 11 Dutch levee stretches have been executed in 3 episodes from 30/10/20 to 28/11/20, 17/02/21 to 31/03/21 and 16/11/21 to 20/12/21. Different test goals have been addressed, to understand the normal performance of a levee cover, and the influence of different anomalies and/or deviations from the ‘standard’ levee.
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This report provides an overview of the initiatives that were taken to disseminate information, lessons and knowledge acquired during Polder2C’s via formal educational programmes and an evaluation of the extent that project findings have been embedded in educational curricula of relevant partner organisations.
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