Oostershelde Handout

Oostershelde Handout - CEG 4011 Soil Mechanics Summer 2006...

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Unformatted text preview: CEG 4011 Soil Mechanics Summer 2006 Presentation “Netherlands: Delta Works Project” Group Members: Jorrel Vaccaro Nick Henriquez David Thomas Jordan Schrader Allison Gilbert Date Submitted: August 7, 2006 Table of Contents: The North Sea Flood of 1953 and the Resolution………………………..………………2 The Oosterschelde Estuary…………………………………………………………….3 - 6 The Maeslant Storm Surge Barrier….…………………………………………………6 - 7 References….…………………………………………………………………………...…8 2 The North Sea Flood of 1953 and the Delta Works Solution • A sudden storm on the evening of January 31, 1953 blew hurricane force winds across the North Sea, causing tidal surges directly towards the Netherlands. • The waves destroyed dikes and dams, and flooded the already below sea level areas of the Netherlands. • 1,835 people and 200,000 heads of livestock died. • 200,000 hectares of land were flooded. • 72,000 people had to be relocated. • To prevent a disaster of this magnitude ever happening again, the Delta Commission was formed, focusing on public safety, maintaining seaways, and regain economic strength. Thirteen barriers have been built to date • Figure1; Flooded Regions . 3 Oostershelde Storm Surge Barrier Figure 1.1 The Oosterschelde Estuary The Oosterschelde Estuary: The Oostershelde estuary is located in the southwestern Netherlands. This delta feeds many estuaries within the Netherlands and experiences harsh waves and tidal surges during the severe winter months. With the progress of the Delta Works almost completed, the Oosterschelde delta was the last delta to be protected. In 1974, the water control and public works agency began designing plans to protect this resource. The following proposals were set forth: • • • Construct an impermeable dam across the 5.4 mile wide mouth of the estuary. Keep the Oosterschelde open and systematically raise the 150 km of dikes around the Oosterschelde. Construct a storm surge barrier composed of multiple gates that would remain open unless severe storm were to occur. If harsh conditions transpired, the gates would be closed either partially or fully. The first proposal was under construction when it was met with heavy confrontation. One major dilemma with building an impermeable dam would be removing an estuary from the ocean. Do you know what would come of this? Creating a dam across the 4 Oosterschelde would eliminate tidal flows which help maintain the ecology of the delta. Salt marshes, oyster beds, mussels and wildlife thrive from the tidal movements of the estuary. Many people make their livelihood from this delta. In 1975, the cabinet proposed the resolution to build the storm surge barrier, although, the barrier would cost more than the dam. The operating costs rose from 5.86 million/year USD for the closed case to 14.65 million/year USD for the storm surge barrier. The advantages were greater than the cost. Construction of the Oosterschelde storm surge barrier: The total span of the storm surge barrier covers 5.4 miles separated by three shorter spans connected by two working islands. The span lengths for the Hammen Gap, Schaar van Roggenplast Gap and the Roompot Gap were 1.179, .717 and .759 miles, respectively. The separation into three channels separated by working islands helps with maintenance as well as anchor points to reduce length of span and excessive forces. The total span connects Schouwen and Noord Beveland. The storm surge barrier consists of 66 prefabricated concrete pillars with 63 flood gates between them. The pillars rise to 15 meters above sea level. The gates are 40 meters wide with heights ranging from 5.5 to 11.5 meters depending on the depth of the channel. The gates can be raised and lowered on demand by hydraulic lifts. The pillar support is supported by a 50 by 25 meter base of concrete. Consolidation of delta bottom: Concerns arose about the immense stress the bottom of the Oosterschelde would be incurring. Thus, an investigation occurred indicating the inadequacy of the bottom floor. Thus, consolidation of the delta bottom was needed. The silt was dredged and replaced by sand. However, the bottom of the Oosterschelde was still too weak to carry the load. Ships such as the Mytilus placed vibrating pipes into the ocean floor. Figure 1.2 on the following page shows the vibrating needle of the Mytilus which was used to compact the sand. The Sand was compacted down to 15 meters of depth. However the compacted sand was still at risk of erosion from the strong North Sea currents. As a result, special mats were fabricated and placed under the pillar foundation. The supporting mats were in the form of a mattress; however, instead of having springs, the mats contained sand and gravel. These mats were constructed of one foot thick plastic webbing, and filled with gravel. The mats were 100 feet wide. Once in place the mats were covered with concrete blocks. The pillars were then strategically placed over the mats. 5 Figure 1.2 Piers and Slides Piers The piers were the most important and complex design of the storm surge barrier. They provided the base and support of the entire dam as well as the pillars, roads and gates. Each pier consisted of 7,000 cubic meters of concrete and construction for each pier took one and half years. The piers ranged from 30.25 to 38.75 meters and weighed 18,000 tons. Two ships were used in the placement of the piers; one to float them to the ship and place them and the other to mark the placement. Precision was needed and the placement took place at the lowest current, during the turn of the tide. The piers were filled with sand for stability and once placed were wrapped in poured concrete. Stones (five million in total) were placed around the piers making the structure immovable. This was important in order for the gates to close. If one gate couldn’t close, the current in the gap would become drastic. High density stones were needed in order to stay put from the rolling tide and current. Slides After placement of the piers, a boat named Bolt could place the slides within the gaps. The slides are driven either up or down by a hydraulic lift. The heights of the slides were determined by the gap needed to be closed. The largest slide was 12 meters high and weighed 480 tons. The dam is operated by humans, but if the human controls fail an electronic security system is a backup. The water level must be three feet above sea level for the gates to close. It takes approximately one hour for one gate to close. The gates have been closed 23 times since 1986 due to predicted or extreme weather conditions. 6 A road was placed atop the storm surge barrier allowing maintenance as well as civilians to save time and distance while crossing from Schouwen to Noord Beveland. Figure 1.3a, details the final look of the storm surge barrier. Figure 1.3b shows the flood warning levels that are used to signal lowering of the gates. Figure 1.4 shows a cutaway of the design of the storm surge barrier. The nature, ecology and beauty of Oosterschelde has been restored with the help of the barrier and as a result in January 2002, the Oosterschelde was officially declared a National Park. The immense design protects Holland from a storm and flood that only occurs every 4000 years. For this reason and the expansive design of the storm surge barrier, the Oosterschelde barrier is considered the eighth wonder of the world. The dam was designed to last for 200 years. The total cost of the project was 3.2 billion dollars. On October 4, 1986 Queen Beatrix officially opened the dam for use. Maeslant Storm Surge Barrier Sill Block Placement and the Filter Bed of the Maeslant Barrier The trench in which the filter bed and sill blocks would be placed was created using dredges. A tow-hopper was used for removal of large amounts of silt in order to dredge the trench. A backhoe was used to form the slopes. The second dredge used was a dustpan suction dredge. This dredge smoothed the trench, and also installed the two bottom filter layers. The bottom protection, which was placed underneath the filter bed, was placed using an inclined stone-tipper. This device was also used for the top two filter layers. In order to create a good seal between the top of the filter bed and the bottom of the sill, the top layer of the filter- bed was smoothed. A dustpan suction dredge was used to do this, also. A steel rake was mounted on the end of the pan in order to form the smoothed filter bed. This method was borrowed from previous construction done in Neeltje Jans and in the Petroleum Harbor. Placing the filter materials in the trench at the bottom of the waterway incorporated several risks. In dumping the material through so much water, there was a concern that the material would separate, and the large particles would sink faster than the smaller ones, causing the filter material to arrive at the bottom poorly-graded. The other risk was of contamination of the filter material with sand and sludge deposited from the tidal currents in the waterway. After researching these issues, it was concluded that dumping the filter materials was feasible. Dredges were also used to place the filter bed material. A modified dredge was used to remove sand and to place coarse sand and gravel. Another dredge deterred the settling of silt and sand due to tidal currents. This dredge directed air and water toward the layers of filter material. 7 Another machine used for this purpose was the Jetsed. The Jetsed removes any sediment deposits in the trench between the filter layers. The Jetsed also utilizes air and water to remove sediment. The machine lifts the bed of disturbed sediment, and the sediment is carried away by the tidal current.The amounts of filter material used were measured very carefully. Accuracy of within approximately 4 inches of the correct thickness of each layer could be obtained. Placing the sill stone was done very accurately as well. The sill blocks were carried over the waterway by pontoon and placed using a floating derrick. The derrick was able to place the blocks with an accuracy of about 1 cm. The position of the blocks was determined by a measurement device attached to each block. After the block was sunk, the device would just barely protrude from the surface of the waterway. 8 1References - DeltaWerken Online. DeltaWerken Online Foundation. 7/15/2006. <http://www.deltawerken.com/English/10.html?setlanguage=en> - Delta Works. Wikipedia. 7/15/06. <http://en.wikipedia.org/wiki/Delta_Works> - SEMP Biot #318: How the Netherlands Defends the Largest Port in Europe Against Flooding. Suburban Emergency Management Project. 7/18/06. <http://www.semp.us/biots/biot_318.html> - New Waterway Storm Surge Barrier. Keringhuis. 7/17/06. <http://keringhuis.nl/engels/ home_noflash.html> - Memory of The Netherland. Koninklijke Bibliotheek. <www.geheugenvannederland.nl> - “How To Maintain Sustainable Development In The Netherlands”. Sustainable Development of Deltas SDD ’98. Oudshoorn, Henk, Bart Schultz, Anne van Urk, and Paul Zijderveld. Netherlands: Delft University Press, 1999. pgs. 279-297. - Catlett, Louis, Sorrel Wildhorn, Richard Stanton, Ary Roos, and Jan al. Controlling the Oosterschelde Storm-Surge Barrier-A Policy Analysis of Alternative strategies. Santa Monica, CA: Rand Corporation, 1980. 9 ...
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