Clear line + Division
The Houtribdijk is situated between Lelystad and Enkhuizen and marks the border between the Markermeer and IJsselmeer. The dike will be reinforced along a 25km stretch. H+N+S Landscape Architects developed a spatial vision to guarantee the spatial quality.
It is necessary to identify and establish the existing qualities of the Houtribdijk in order to maintain these. In this way, clear designing principles can be developed to integrate improvement measures. This integrative vision puts this into practice.
The clear line and the division
The history and future of the dike are clearly linked to the subsurface; the sandy reinforcement reacts to the Enkhuizer sand. This relation is made visible and offers opportunities for nature development. The Houtribdijk is experienced as one iconic hydrological engineering structure. This unequivocalness will be challenged when the dike is reinforced. Therefore, the dike will have one continuous base profile. In this way the dike will remain intact as a clear and empty line in the middle of the largest fresh water reservoir in the Netherlands.
We started describing the characteristics of the dike on two scale levels: the dike and its surroundings and the dike trajectory itself, including the cross section. Subsequently, the safety task was summarized and compared to the conclusions from the analysis. The spatial tasks for the integrative design are formulated from this. The final step in the process is the development of an integrative vision in which the spatial quality ambitions for the project are outlined on the basis of design principles. Subsequently, the integrative vision was translated into an Aesthetic Programme of Requirements.
The analysis showed that the Houtribdijk is carefully designed as one iconic hydrological engineering structure with a richness of materials on various slopes. Furthermore, the dike has been built as a scenic route. The qualities from the original design will remain the starting point for the new dike design.
The dike reinforcement results in a dichotomy of the dike: the sandy solution and the quarry solution. In order to maintain the dike’s coherence as one continuous line, a clear narrow road profile with contiguous verges along the entire dike trajectory needs to be constructed. As a result, the road has the same profile along its entire length. The location of the N302 remains unaffected.
The Houtribdijk cuts across a large part of the Dutch landscape and is hardly visible from the surrounding area. Therefore, the main starting point is to focus on the current use (flood defence, road and bicycle path) and not to add a spatial impact programme that will impair the uniform image of the flood defence. An exception is made for the Trintel and the landing ends of the dike, which will manifest themselves much more as islands to this empty line.
The history and future of the dike are closely connected with the subsurface. The sandy solution for the dike reinforcement, for instance, reacts to the Enkhuizer sand. This relationship with the subsurface is made visible in the dike design, creating an important opportunity to reinforce natural values. The subsurface offers conditions for nature development.
The sandy solution is applied to the north west of Trintel. The landing ends of the (current) dike are situated as a continuous prominently designed profile on top of the sandy and more natural bank area.
The quarry solution is applied to the deeper part to the east of Trintel. The layers (zoned structure made of different materials in relation to the slope’s position) are to be maintained or restored in the new dike profile as much as possible. The cross sections of the dike need to be designed uniformly to create coherence and continuity in the linear profile. Sharp and distinctive transitions are applied between the materials of the dike.
Trintel sand is mainly realized 2,5 meters above sea level outside of the current foreshore dams. A larger surface is created with shallow environments with water plants, suitable as spawning ground for fish and feeding area for fish eating species, dabbling ducks and waders. Reed beds will also be developed as a suitable niche for reed warblers/marsh birds. There is also a focus on developing sand banks, shallow bay areas and wetlands.
In addition to developing the integrative vision, H+N+S was involved in formulating assessment criteria for the contract and will act as supervisor in the implementation phase.
