Ex1: Adaptive Afsluitdijk

Adaptive Afsluitdijk

General Info:

Project by: Monique Sperling, Netherlands
Location: Northern Netherlands, NL
Client: Wageningen University MSc thesis
Completed: 2009
Link: Thesis report PDF

Description:

Landscape as infrastructure for coastal safety

‘The Future of an Adaptive Afsluitdijk’ presents a 21st century design for a safe and ecologically improved barrier dam that expresses the unique qualities of the site. The design focuses on a dam originally built in 1932 to close off the Souther Sea, that allowed for better flood protection of the Dutch hinterland, cheaper maintenance, improved transportation routes, and created the possibilities for several large-scale land reclamations. Its construction changed the sea south of the dam into a huge fresh water storage basin, the IJsselmeer [IJssel lake], as it is constantly being filled with by water from the IJssel river. Fresh water is regularly discharged (spouted) at low tides by use of gravity from the lake into the Wadden Sea in order to maintain safe water levels within the basin.

At present, the dam—an icon of Dutch technical water engineering excellence—is outdated; it does not meet the demanded safety regulations and needs to be redesigned in order to provide for the high safety standards set for the coming decades. But just as important, Dutch society has changed since 1932 and the dam is now seen as lacking perceptional experience and being mono-functional and ecologically ignorant; it causes a huge barrier in the natural river estuary system, separating saline from fresh water ecosystems, blocking migrating fish from moving up the rivers, and obstructing species exchange. The occasional spouting of large amounts of fresh water from the IJsselmeer into the brackish Wadden Sea causes abrupt environmental shock and results in illness and mortality of sea life.

The Future of an Adaptive Afsluitdijk presents a landscape (space) solution for a defence (line) problem. By use of natural dynamics and artificial construction, a defence landscape will evolve that can incorporate ecological, experiential and renewable energy aspects next to the technical safety standards, while adding to the uniqueness of this iconic site. During the design process three models were developed: A) raising the dam; B) a natural barrier along the existing dam; and C) a second dam along the existing dam. After signification of the guidelines and assessment of the spatial models, model B turned out to be the best model from a landscape point of view.

How it works

The design concept is based on the history and characteristics of the site. In order to increase the safety standard of the dam, both artificial and natural-system methods are used. The design starts by reconfiguring the profile of the dam. By moving the bicycle path to the other side (IJsselmeerside)of the dam, space is provide to raise the dam with 2,35 meters while maintaining the highway and simultaneously improving the views from the bike route. Between the bicycle path and the highway, a slope is constructed to separate fast and slow vehicles and counter noise pollution. This slope is optimized for placement of solar panels along the full length of the dam, providing up to 320 MW of harvestable renewable energy (Energielijn 2008 cited in Sperling, 2009: 80), clearly in sight of bicyclists. The vast openness of the dam is further emphasized by increasing the contrast with the headlands. This is done by enlarging the forests at the Noord-Holland abutment and adding a ´forest´ of wind turbines at the Friesland abutment.

On the northern side of the dam, light measures are taken to start and accelerate the accretion of silt and succession of salt marshes. Salt marshes have a huge natural potential of functioning as a natural barrier able to dim large waves and can grow along with the expected sea level rise (Dijkema et al. 2007 cited in Sperling, 2009: 100 ), hereby being intrinsically adaptive. In order to augment the processes of salt marsh genesis, wicker dams are placed in strategic locations and boulder clay is added as a basis. Water flows, depths, ecology and sandbanks are taken into account. In a later stage, and depending on natural development, marsh growth can be further accelerated by seeding or planting saline grasses and plants and optional silt nourishments. The change over time will add to the beauty of the site and will appeal to visitors and tourists. Due to the vast scale and importance of the implementations, monitoring growth and erosion of the salt marsh barrier is essential.

Due to the location of the ‘Doove Balg’ trench—touching the dam along the eastern side—and the fact that this is the deepest part, it is financially and technically infeasible to protect the entire northern side of the dam with salt marshes, since they will be washed away by strong water currents. This area will be protected by building artificial reefs out of basalt blocks. The height of these reefs is adjusted to the tidal levels of the sea; at low tide the reefs are visible, while during high tide they are invisible. By doing this, the tidal dynamics of the site can be well experienced and visitors are more aware of the natural forces present.

The salt marshes, being system-native and rare, have a high ecological value and contribute also to the cleaning of the water. They filter the silt out of the water so that this water can be used in a newly proposed osmosis plant at ‘Breezanddijk’. This osmosis plant—open to the public for educational uses—makes use of the fresh IJsselmeer water and saline Wadden Sea water to produce sustainable energy and can produce about 500MW. The brackish ‘waste’ water of the osmosis plant is used in combination with the optimal positioning of the reefs to make a lengthy fresh-saline water gradient that is mixed by natural current and turbulence. By smart discharging the osmosis residue water and leading it to the spouting sluices, the spouted fresh water will first get mixed with brackish water before mixing with the saline Wadden Sea water. Migrating fish will find this brackish water flow and swim in the direction of Breezanddijk, because of the gradient in salinity (van Duin 2008 cited in Sperling, 2009: 112). Near the osmosis plant at Breezanddijk, the same brackish residue water is now used for creating a fresh-saline fish ladder, allowing diadromous fish species to pass the dam and migrate up the rivers. A strolling path passing the marshes connects the village of Den Oever to the Vlieter monument and osmosis plant

As a whole, the design presents an integral landscape solution for a safe Afsluitdijk that is beautiful, contextual and adaptive to unpredictable climate change. The design can produce renewable solar, osmosis, tidal and wind energy for up to 538.000 households. The spatial quality of the open horizon and the long, straight line are strengthened, while better fitting the natural conditions and local context. The design now shows a multifunctional Afsluitdijk in which the production of renewable energy, and the increase of ecological values and visitor experience, are integrated with the main functions of providing safety, spouting water, and being a passenger connection.

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