Reinforcing the Houtribdijk: a world first in water safety and nature conservation

The Houtribdijk reinforcement project was a world first in combining water safety with opportunities for nature and recreation. The project has created a dyke that is able to withstand storms that occur once every 10,000 years, while also providing a new home for wildlife and a space for people to enjoy the outdoors.

As a result, residents in the IJsselmeer area will be protected from the effects of high water levels for decades to come. The reinforcement of the Houtribdijk is part of the Flood Protection Programme (HWBP), the largest dyke reinforcement project 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.

The Houtribdijk: origins

The Houtribdijk is 32 km long and connects the provinces of Noord-Holland and Flevoland in the Netherlands. It was built between 1963 and 1976 to reclaim land in what is now the Markermeer. However, when the reclamation plans changed, the road on the dyke remained an important link between the 2 provinces.

The Houtribdijk is also important as a flood barrier. During storms, it absorbs the force of the Markermeer and IJsselmeer, and it protects the surrounding provinces against storm surges. Thanks to the reinforcement, which began in 2017 and ended on 22 June 2020, 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 carried out in a sustainable manner, based on the principle of recycling, by carefully assessing the old stone and reusing it wherever possible.

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

More than 50 ha of new, 'wet nature'

One of the largest ‘additional’ interventions is the creation of Trintelzand, a 532 ha nature reserve with sand dunes, mudflats and reed beds. This nature reserve was created using surplus sludge from the dredging of the dykes. Creating the nature reserve is more cost-effective than disposing of the sludge.

The reserve is suitable for mussels, snails and aquatic insects and acts as a nursery for fish. The aquatic life will provide food for bird species such as the tufted duck, common tern and great crested grebe.

Largest dyke reinforcement project since the Delta Works

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

Over the next 30 years, at least 1,100 km of dykes and 500 locks and pumping stations will be reinforced. Together we are working to make the country a safe place for living, working and recreation.