Coastal flood managers seek to anticipate future flood risk and as a result consider the adaptation of flood defences. Instead of crest heightening, dikes can be adapted to include hydrodynamic reducing vegetated foreshores to form a nature-based hybrid flood defence, for instance; at managed realignments. In this study we investigated the potential of vegetated revetments as a natural continuous connection between the realigned dike and restored foreshore. We applied the historic grass sod transplantation technique with the aim to improve our understanding of the strength of a transplanted sod revetment. In Living Lab Hedwige-Prosperpolder, dikes were available for in-situ experiments during managed realignment preparations. We transplanted grass sods and studied erosion resistance after one growth season. Our results show transplanted sod vegetation continued to grow and started to attach to the clay layer. While erosion occurred under extreme wave impact and overflow, the sod pulling method revealed individual sod strength. In conclusion, sod transplantation is a good technique to source local material for green realigned dike revetments. A vegetated dike revetment can hereby create a natural continuous connection between the realigned dike and foreshore, which benefits flood protection as well as flora and fauna. ... Read more

Design criteria for the stability of rock filters on river beds (i.e. rock bed protection) are extensively researched and successfully applied in practice. The most common stability criteria are the Izbash and Shields criteria. These methods define a critical flow (Izbash) or parameter (Shields). Rijkswaterstaat (RWS) wants to explore a more sustainable bed protection by using logs. A pilot project is started where logs will be used as bed protection. It is yet unclear if the design and construction approaches for rock bed protections can be used for log bed protections. The most dominant aspect is that logs are cylindrical objects, while rocks are spherical. This means that the design criteria for rock filters might not be directly applicable to log filters. This research aims to verify if the Izbash and Shields criteria for rock can be used for logs to create functional and safe designs. To achieve this, two experiments are performed at the TU Delft faculty of Civil Engineering & Geosciences. The first experiment, done in a water filled tank, explores the settling behaviour of logs for multiple drop methods. Insight is gained in the settling velocities, horizontal spread and magnus effect (force exerted on a rotating object, e.g. the curve of a football spinning through the air) of logs settling in a water column. Results from these experiments are used in the second experiment. This experiment is done in a 14.3m long flow flume where a log filter is constructed. The log filter is constructed using the drop method that was preferred from the first experiment. The roughness, stability and porous flow of a log filter are investigated. The results are compared with what is known for rock filters. Tree branches were used as model logs. This was done to be able to correctly scale the results to prototype scale. Primary reason for this was the effect of bark on the roughness of a cylinder. This is difficult to replicate on model scale. Using branches of trees that will be used Saturating the model logs however was more time consuming than initially expected. Attempts were made to accelerate the process but they were futile. One method, using a diaphragm vacuum pump, could not be applied due to lack of resources. For any future research on the topic of tree branches as model logs it is highly recommended to use a vacuum pump to ensure that the maximum density is reached. From the first experiment it was concluded that large quantities of logs can still be used to create functional log filters. This is a positive result as this will reduce construction time on prototype scale. The method used was a funnel. This method was applied in the flume to create the log filters. By measuring the velocity profile for multiple discharges the roughness of a log filter was measured. This also resulted in an equation of the shear velocity as a function of the discharge. By increasing the discharge step by step, several mobility stages of a log filter were found. This resulted in a dataset that could be directly compared with the Izbash and Shields equations for rock. Higher critical Shields parameters were observed than for rock of the same diameter. The behaviour of a log filter differed from a rock filter in the transition from one stage to another (stable to mobile to transport to failure) did not occur slowly, but almost instantaneous. This behaviour is unwanted because it is difficult to monitor in what stage a log filter is if no changes can be observed between stages. Thus, although applying the equations for rock filters to log filters are conservative, the behaviour of log filters are more sudden and prone to escalation close to their critical thresholds. Final conclusion is that more research is required to better understand the significance of variables for the settling behaviour and stability. These are water depth, log diameter independent of density and vice versa, log orientation and log length to diameter ratio. This can be done by doing more experiments in a similar fashion where only one variable is changed at a time. For the application of the design criteria for rock to a log filter with regards to the pilot project, it is recommended to be conservative. Based on these experiments it is safe to assume that when the most unfavourable scenario is used (e.g. low log density, small log diameter, high flow velocities near the bed) a sufficient design is made, especially if the top layer(s) of the filter are placed parallel to the flow direction. Backfilling of the log filter did not increase the stability significantly in this research and is only be beneficial for scour protection. ... Read more

All around the world floods are a growing problem. Dealing with high water levels in residential areas is of great importance. The delta area of Macabebe, in the Manila Bay, has to cope with daily flooding, caused by the river and the sea. Groundwater is pumped and used for local industry, causing land subsidence and worsening the problems. Where once rice fields were the main source of income, these fields are now fishponds where fish escape during a large flood. Additionally, typhoons strike the region regularly. Due to climate change and the ongoing ground subsidence the problems won’t lessen, so a solution needs to be found. In the Netherlands, multiple organizations are working daily on finding solutions. One of these is Finch Floating Homes, who designed a typhoon resilient, floating home for in the Philippines. This design had to be elaborated on before construction of a pilot project. This report contains the needed changes and advice for the design of the floating home. Through research, local interviews and analysis, the design of the house has been improved on the roof, sanitary system and mooring system and a construction plan has been created for the pilot project.

Based on a revision of the roof shape, the hip roof turned out to be the best shape in a typhoon prone area. During the design, the geometry of the housing unit was slightly changed into a double symmetrical geometry, increasing constructability and simplicity of the house. The design of the roof structure and its connections, consisting of four identical prefabricated frames, is presented. After prefabrication, the frames will be connected on-site, after which the newly designed foldable balconies will be placed in the frames. The material used in the design is corrugated steel roof sheeting.
The final roof shape is used to calculate the rainwater collection. The floating house requires a self-sustaining system that fulfils the needs of drinking water and wastewater treatment. This
system consists of three separate systems: (1) rainwater harvesting, consisting of a drainage system, first flush barrel system and sand filter. (2) Storage of water, capable of storing sufficient water for one-third of the total usage over 80% of the year. (3) Wastewater, based on natural treatment before discharge into the surface water, containing a septic tank and wetland filter.
The water management system within the foundation, the wind load on the house, waves and currents influence the motions of the floating structure and the forces on the mooring system. An analysis of the options for mooring systems leads to the decision of using mooring piles. The total stiffness of the piles influences the horizontal motion and rotation of the platform. The vertical motion is a free behaviour; it is not influenced by the mooring piles. It is needed to choose a specific combination of pile length and bending stiffness, after which the strength of the pile is checked.
The design is used for the project construction plan, focussing on the time, risk and change management of the pilot project. The resources and construction activities and their duration were identified to develop a schedule for controlling the construction phase. Preparations and construction of the pilot will take 13 weeks, but includes several risks. Response strategies for these risks are proposed, to use for a risk mitigation plan. Finally, advice is given on how to manage possible design changes regarding new research, development of design and up-scaling changes after a successful pilot project.

With the use of this report and more detailed research and design, the pilot project will be an optimal test of the floating house in the Philippines.
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Wood can be used to rehabilitate degraded water bodies (lakes and rivers). However wood has historically been removed from river systems to improve flood protection, inland navigation and drink water quality. These actions reduced and degraded the aquatic habitat of the effected river systems. Rijkswaterstaat is interested in reintroducing wood to rehabilitate the aquatic (and terrestrial) habitat of river systems.

In order to successfully reintroduce wood in river systems it is necessary to identify where the wood comes from? How is it transported? How does it accumulate? And what are the effects on stream ecology and geomorphology? This knowledge can be used to determine if already naturally occurring wood in river systems can be managed to achieve the goal of river rehabilitation. If no or too little wood is present in the river system, an engineered solution can be used. This engineered solution is known as Engineered Log Jam (ELJ). These structures use wood as construction material to rehabilitate rivers. The stability, design and implementation of ELJs in rivers is a complex process.

This report provides an overview on the identification, classification, importance and management of wood in river systems. Secondly the gives an overview of studies done on the stability of wood in rivers, the design (process) of ELJs and the geomorphological impact of ELJs on river systems.

From the studies reviewed in this report it is clear that wood plays an important role in river systems. Wood directly effect river ecology and geomorphology by forming log jams. Proper management of wood is therefore required if one wishes to retain a healthy river system. Where one wishes to (re)introduce wood in a river system using ELJ structures the design process is vital. The first step is to identify the characteristics and properties of the river section. The second step is designing the correct ELJs for the desired goals. The last step is constructing and monitoring the ELJs. Evaluation is important to obtain points of improvement. ... Read more