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Afsluitdijk upgrade in the Netherlands.

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Afsluitdijk upgrade in the Netherlands.

Rechten: https://hbokennisbank.nl/pages/open-access

Samenvatting

Numerous flood disasters occur every year worldwide, mostly resulting from failure of dikes, some with catastrophic outcomes. Examples are the dike failures along the Yangtze River in China 1931 due to heavy rainstorms; in the Netherlands in 1953 due to a storm surge at the North Sea and in 2005 in the United States, New Orleans due to Hurricane Katrina. These floods induced many deaths and economic losses. The consequences of a flood by a dike burst can vary strongly and depend mainly on the speed and rate of inundation of the bordering land.

As long as mankind remembers the Netherlands has been a sinking country bordering the rising sea. Approximately 25% of its surface is below mean sea level. The lowest point north east of Rotterdam is 6,7m below mean sea level. In the absence of dunes and dikes more than 65% of the country would be flooded at high sea and high river levels. This situation makes the Netherlands very vulnerable to storm surges and river floods.

A line of defense has been constructed in the North West of Holland to counter rising water levels namely the Afsluitdijk, which dates back to 1932. The design life of the structure has almost been outlived, but future conditions threaten the existence of this structure, ultimately human lives are at stake. For the current situation the dike is 7.8m + NAP with an outside slope of 1:4 covered with basalton as a revetment with a permeable clay layer on top of the crest covered with grass with a inside slope of 1:3,5 . 6 and with a width of 80 . 100m, refer to a detailed drawing in Appendix B, (dwg. no. RWS. CURRENT PROFILE). If the current structure faces these severe storm conditions it would mean that a wave overflow of approximately 366 /s/m will occur, rising Lake Ijssel.s water level by 0.5m over storm duration of 12 hours.

The upgrade can be done in several ways, each possible solution has its advantages and disadvantages. This report focuses on these differences and expresses findings in a manner that will help the Ministerie van Verkeer en Waterstaat to make an informed decision on the best upgrade. Calculations were made on fourteen different alternatives. The results were then compared with each other, where only four were considered, with cost, safety, practicality and the time factor for how long the construction would take, to be the main factors on selecting the most suitable solutions.

All calculations in this report are based on a 1 in 10 000 year storm.This means a wave height of 3.5m, a sea water level of 5.8m above NAP (Amsterdam Ordnance Datum) and wave period of 8.5 seconds reference (.Rijkwaterstaat, Water en Bouwdienst division . Wim Kortlever.).

The upgrade solutions resulted from conclusions are: •;Forming a dune parallel to the Afsluitdijk with a breakwater: A dune with a height of 13.5m + NAP, with a breakwater height of 4.5m + NAP which would be acting as a tombolo structure to ensure that erosion of the dune is minimized and help with nourishing of the beach, with a slope of 1:50 - :100, against a erosion of 2.2 m3/m during the 1 in 10 000 year storm. •;Reinforce the Afsluitdijk with a berm and stronger slope protection: Keeping the existing structure and slope by introducing a berm with a width of 10m at the height of the storm surge level of 5.8m + NAP where most of the wave energy would be dissipated, also by placing heavy revetments with a low roughness factor on the outside to help reduce wave height and overtopping, the inside slope replaced with a hard cover to ensure the structure integrity stays the same.

Although the overtopping would be 14 /s/m it will not have a big influence in the Lake Ijssel, because at a storm intensity of 12 hours the water level will only rise by 0.02m which the Polders and dikes along the Lake Ijssel could easily handle. •;Enlarging the Afsluitdijk with higher crest height and new slope: Lifting the crest height to 9,8m + NAP and changing the slope to 1:6, will result in minimum overtopping and over flow. Maximum overtopping of 4 /s/m will occur for overflow.

;Enlarging the Afsluitdijk with higher crest height; berm and current slope: The crest height is raised to a new level of 9.8m + NAP and the existing slope of 1:4 is kept, but a berm of with a width of 10 m is introduced at the design storm surge level of 5,8m + NAP. A safe overtopping value of 6 /s/m and a maximum rise of 0.01m in the water level of the Lake Ijssel are calculated. Practically the slope and berm help with the reduction in wave run.up and overtopping. International Bachelor Degree in Civil Engineering 8 Upgrading of Afsluitdijk Holland From the solutions above, certain advantages and disadvantages are revealed: •;Forming a dune would have very high aesthetical value and also a natural barrier against the high sea, but it is costly due to large volumes of material needed and would need the regular volume to nourish the dunes and beach. The breakwaters which would act as tombolo.s are only practical in shallow water with reducing wave height sufficiently and also cheaper to construct in lower water level. •;Reinforcing the dike could be the most practical solution because it changes the cross section of the Afsluitdijk the least, but placing the heavy revetments is costly. The hardcover on the inside slope would not be of a high aesthetical value.

The remaining alternatives were not considered from the certain criteria aspects laid out in Chapter 4. For the purpose of this thesis no extra designing went into the sluice gates and bridges, further investigation and designs would be needed to be undertaken to ensure that these structures get upgraded with the rest of the Afsluitdijk.

Toon meer
OrganisatieHogeschool Utrecht
OpleidingCiviele Techniek
AfdelingGebouwde Omgeving
PartnersMinisterie van Verkeer en Waterstaat
Jaar2007
TypeBachelor
TaalEngels

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