International Dredging Review

International Dredging Review

Map of the northern part of the Netherlands showing the Afsluitdijk and the Houtribdijk as well as other existing dikes that are crucial to the Netherlands Flood Protection Program.

In December 2016 the Netherlands Directorate General for Public Works and Water Management known in Dutch as Rijkswaterstaat announced its intention to grant permits for the reinforcement of the Houtribdijk to two Dutch dredging companies Royal BoskalisWestminster N.V. Boskalis) and Van Oord. As of late January that project is set to proceed with a contract that carries a value of 90 million euros (about 96 million dollars) to be divided evenly between the two companies. The project is part of the Netherlands’ national Flood Protection Program (Hoogwaterbeschermingsprogramma)

To understand the significance of the Houtribdijk (dike) work one has to go back to the 1920s when the “Afsluitdijk” was constructed. The Afsluitdijk was a ‘closure dike’ built from 1927 and 1932. It dammed off the Zuiderzee (South Sea) a large shallow saltwater inlet of the North Sea and created a freshwater lake known as the IJsselmeer (meer = lake). This was a basic section of the larger Zuiderzee Works which was the one of the largest hydraulic engineering projects in the Netherlands during the twentieth century. These dams dikes and land reclamation created polders for agriculture and at the same time provided improved flood protection.  

It also created a connection across the northernmost part of the Netherlands to two regions of the country that could only reach each other by boat or by a very long drive around the coast of the Zuiderzee. The dike became a major causeway that goes from Den Oever in the Province of North Holland to the town of Zurich in the Province of Friesland. Its length is some 32 kilometers (20 miles) and it is 90 meters (300 feet) wide and more than 7 meters (about 23 feet) above sea level. The construction of this dike resulted in major economic and social development for the northern provinces. 


Old Infrastructure Not Meeting Safety Standards

The Houtribdijk was built some 35 years after the Afsluitdijk and also crosses the IJsselmeer connecting two distant cities with each other plus providing crucial protection against flooding. Construction of Houtribdijk started in 1963 and finished in 1975 separating the original IJsselmeer into the Markermeer on the southwest side and the IJsselmeer on the northeast. The Houtribdijk connects the city of Lelystad built on the new polder of Flevoland with Enkhuizen a town in the Province of North Holland. This dike also protects large parts of the Netherlands from flooding by preventing water from the IJsselmeer from overflowing into the Markermeer.  

After several recent studies the Netherlands government concluded that the dike now more than 40 years old does not meet its safety standards. According to the Rijkswaterstaat “The Houtribdijk between Enkhuizen and Lelystad protects a large area of the Netherlands from rising waters. When measuring the norms for water safety according to national standards it became apparent that improvements are necessary to ensure that the hinterlands of the Netherlands will be safe in the long term.”

Rijkswaterstaat consequently decided that the strengthening of the Houtribdijk over a distance of about 25 kilometers (15.5 miles) was necessary. After much thought planning and input from stakeholders the plans were ready and from November 3 to December 16 these plans were presented to the public and the regional Water Boards for final discussion. Since no objections were made in this six-week period the operations are now set to go forward and the contracts for dredging were awarded to Boskalis and Van Oord. 

The project entails the reinforcement of the Houtribdijk on both sides with sand and rock over a distance of 25 kilometers (15.5 miles). The work is planned to start this year and should be completed in 2020. At that time the dike should once again meet the legally stipulated safety norms of the country. The dike reinforcement project is part the Dutch Flood Protection Program an alliance of Rijkswaterstaat and all district Water Boards aimed at reinforcing primary dikes in an innovative and robust manner.

After the completion of the reinforcement of the Houtribdijk the chance of a collapse of the dike will be reduced to once in 10000 years. In addition the restored and enhanced dike will offer more opportunities for nature and recreation. 


Other Reinforcement Work

Also as part of the Dutch Flood Protection Program Boskalis is currently working on the reinforcement of the Wadden Sea dike on the island of Texel the reinforcement of the Wadden Sea dike between the towns of Eemshaven and Delfzijl as well as making sure that dike is earthquake-proof and the reinforcement of the Markermeer dikes between the towns of Hoorn and Durgerdam. Van Oord is also executing various dike reinforcement projects that are part of this program to protect the country from flooding including the recently awarded project Den Oever and the reinforcement projects of dikes on Dordrecht Island and the dike between Hagestein and Opheusden which are on the major rivers in the southern part of the country.

All these projects are a cooperative effort between Rijkswaterstaat and the Dutch Water Boards and form part of the Dutch Delta program. According to Rijkswaterstaat “The policy of the Dutch government is to prevent a disaster before it happens by ensuring that very strict safety standards are in place. The result of this approach is the Dutch Flood Protection Program which is presently beginning the largest dike improvement operation ever before implemented.” 

More than 1100 kilometers (688 miles) of dikes and 256 sluices and pumping stations will be worked on from now through 2028. More than 300 projects are spread all over the Netherlands along the coast on the banks of the major rivers and in lakes. In total 7.4 billion euros (about 8 billion dollars) have been reserved by the Flood Protection Program for these dike improvement works