Reinforcement of the Houtribdijk

The project to reinforce the Houtribdijk is a world first! The reinforcement of the Houtribdijk is a unique dyke reinforcement project, combining water safety with opportunities for nature and recreation.

Former minister Cora van Nieuwenhuizen (Infrastructure and Water Management) announced the completion of the Houtribdijk reinforcement project on 22 June 2020. The dyke between Lelystad and Enkhuizen can now, thanks to a new layer of quarry stone and enormous loads of ballast, deal with the sort of storms that occur once in every 10 thousand years.

This means that local residents in the IJsselmeer area are protected against the effects of high water levels for the next few decades. The reinforcement of the Houtribdijk forms part of the Flood Protection Programme (HWBP), the largest dyke-reinforcement operation since the Delta Works.

Houtribdijk reinforcement: Building with Nature (March 2019)

The Houtribdijk was built in the 1960’s and 1970’s. Originally, it’s purpose was to create new land in the Markermeer. Now it links the province of North Holland to Flevoland. We are reinforcing the Houtribdijk with large loads of sand. This natural building material comes from nearby the levee. Hydraulic filling deposits 10 million cubic metres of sand. This sand is shaped into wide, sloping banks. These slopes will absorb the force of the waves. The transition between water and sand will also benefit natural diversity. This type of reinforcement in a freshwater environment is a world first. Scientists are monitoring how sand and waves affect each other. This increases our knowledge of innovative, nature-based reinforcement. Ensuring smart protection of the Netherlands, by building with respect for nature.

As Minister Cora van Nieuwenhuizen says: ‘After this refurbishment, the Houtribdijk is now fit to face the coming decades. It not only offers protection against the sort of extreme weather conditions we now face. This project has also created a natural area the size of 900 football pitches and there is more space for recreation, such as a new watersports beach at Lelystad.’

The Houtribdijk

The Houtribdijk was built between 1963 and 1976 with the aim of reclaiming land in what is now the Markermeer. When the reclamation plans changed, the roadway on the dyke remained an important connection between the provinces of Noord-Holland and Flevoland.

The Houtribdijk is also important as a flood barrier: during storms it absorbs the force exerted on it by the Markermeer and IJsselmeer, and it protects the surrounding provinces against storm surges. Thanks to the reinforcement, work on which commenced in 2017 and is now complete, the Houtribdijk is well equipped to meet this challenge in the future.

World first with sand

At the Enkhuizen end, the dyke has been reinforced with 10 million m3 of sand; an amount equal to the volume of sand that is deposited along the entire Dutch coastline in 1 year under normal conditions. This natural construction material was dredged from the adjacent Markermeer and deposited by rainbowing. Then the individual loads of sand were placed against the dyke.

This form of 'Building with Nature’ is more environmentally friendly and cost effective than traditional solutions, helps improve water quality and increases the diversity of nature in the area. Nowhere else in the world have broad sand embankments ever been used in a freshwater area not subject to tidal activity.

Over the next few years Rijkswaterstaat, in collaboration with the TU Delft, will be investigating how the embankments change, so that the knowledge acquired can be applied in a wider context, both in the Netherlands and abroad.

Recycling of stone

At the Lelystad end, the Houtribdijk was reinforced with 1.2 million tonnes of rubble and 100,000 tonnes of mastic asphalt. The project was implemented sustainably, on the basis of circularity, by carefully assessing the old stone and re-using it where possible.

The dyke is now so strong here that waves can wash over the dyke in the event of a major storm without creating any problems. And at Lelystad, a new watersports beach has been created for the province of Flevoland: the Bataviastrand.

More than 50 hectares of new, 'wet nature'.

A new nature-conservancy area, Trintelzand, with an area of more than 500 hectares, emerged alongside the dyke. This natural area was created using excess sludge from the process of dredging for the embankments. The creation of the nature-conservancy area is more costeffective than otherwise disposing of the sludge.

Trintelzand forms part of the 'New Land’ National Park and is made up of long, curved dams with sand bars, shallows and marshy areas in between.

Below the water level, a whole new living area and spawning ground for fish and other aquatic life is being created. Above the water, Trintelzand is a new foraging place full of nutrients for birds in the IJsselmeer area: flamingos have even been sighted at the snack bar near the Marker Wadden.

Largest dyke reinforcement operation since the Delta Works

Rijkswaterstaat's reinforcement of the Houtribdijk formed part of the national HWBP. The reinforcement of the Houtribdijk was carried out by a partnership of contractors, Boskalis and Van Oord, working under the name of 'de Combinatie Houtribdijk'. The water boards and Rijkswaterstaat are working together under the HWBP on the largest dyke reinforcement operation since the Delta Works.

Over the next 30 years, at least 1100 km of dykes and 500 locks and pumping stations are scheduled for reinforcement. Together we are working to make the country a safe place for living, working and recreation.