Basic documentation Maeslant Barrier

Base Module 1

Principles of Operation - Introduction 1

This module covers the choice for and the operating principles of the Maeslant Barrier, also known as the Storm Surge Barrier in the New Waterway. The module will give you insight into the history of the design and discuss the boundary conditions. In addition, the relationship with the storm surge barrier in the Hartel Canal (SSBHC) will be explained.

The workings of the Maeslant Barrier are discussed next, and the process of a complete closure is covered by means of theoretical storm scenarios.

Objective of this module is to make the reader familiar with the background and general operating principles of the Maeslant Barrier relatively quickly.

This base module is part of a larger collection of documents. The documentation comprises two base modules and five handbooks. The five handbooks are the following:

Handbook 1: Dock and dock door Handbook 2: Barrier and lattice arms

Handbook 3: Drive mechanism (locomobile) Handbook 4: Ball joint

Handbook 5: Civil/Grounds/River

Contents of this module 1 History

2 Commission Storm Surge Barrier New Waterway

3 Purpose of the Barrier

4 The six designs

5 Performance

6 Location and Europort Barrier

7 Operating principles of the Maeslant Barrier

 Directorate-General for Public Works and Water Management, Central Division of Public Works and Water Management, P.O. Box 20906, 2500 EX The Hague, The Netherlands. All rights reserved. No part of this publication may be reproduced, stored in an automated data file, or made public in any form or in any manner, electronically, mechanically, by photocopying, recordings, or any other means without prior written permission from the publisher. This also applies to entire or part renditions of this publication.

1

History

Whenever there is a high tide level of 3.00 meters above Amsterdam Ordnance Datum (NAP), half of the Netherlands would be inundated if the sea had free reign. Fortunately, there are dunes (natural protection) and dikes (artificial protection) that safeguard us against high storm surges. In addition to these forms

storm surge barriers of protection, there are storm surge barriers. The phrase “storm surge barrier” is

used to indicate a construction with movable parts, which is closed when the water level is dangerously high. Such a construction usually has sliding panels, flaps or doors.

Delta Plan These storm surge barriers can also be recognized in the Delta Plan, such as the

Haringvliet sluices and the storm surge barrier in the Eastern Scheldt; see Figure 1.

Figure 1. The Delta Plan

a. Brouwers Dam 1972 b. Haringvliet Sluices 1971 c. Volkerak Dam 1969

d. Storm Surge Barrier Hollandsche IJssel 1958 e. Zandkreek Dam 1960

f. Veerse Dam 1961 g. Grevelingen Dam 1965

h. Storm Surge Barrier Eastern Scheldt 1986 i. Philips Dam 1987

j. Oyster Dam 1986

The Delta Plan dates back to 1954 and its objective is increased protection against flooding. Its inventors and builders faced a major challenge. The Western Scheldt and the New Waterway had to remain open for economic reasons.

main barriers It was decided to strengthen the existing main barriers along the Western Scheldt

and around Rotterdam and Dordrecht. The phrase “main barrier” is used to indicate a dike or storm surge barrier of such a size that it offers sufficient safety for the area behind it.

2

Commission Storm Surge Barrier New Waterway

dike strengthening Dike strengthening in the Province of Zuid-Holland stagnated in the 1980s.

Notably in urban areas, dike strengthening has major consequences for the landscape. In the 1980s, it was the difficult urban areas’ turn. Particularly in Rotterdam and Dordrecht and its surroundings, dike strengthening would have very dramatic consequences. See Figure 2.

In addition, new calculations and modified assumptions of expected water levels revealed that the dikes that had already been strengthened would have to be raised even more.

In April 1987, the Minister of Transport, Public Works and Water Management ordered an investigation to determine whether a storm surge barrier in

combination with only limited raising of dikes would be an attractive alternative for continued strengthening of dikes. This investigation was carried out by the Commission Storm Surge Barrier New Waterway (CSSBNW), which brought together the expertise of the Directorate-General for Public Works and Water Management and of the industry. This commission set to work energetically. A contest was held and led to the selection of five contractor combinations that were invited to submit designs and budgets. Three months later, on 1 October in the same year, six designs had been received. When it became evident that the construction of a storm surge barrier in the New Waterway was technically feasible, the Council for Transport, Public Works and Water Management started studying the matter. The year 1988 was used to draw up the environmental impact assessment (EIA) and to develop some of the designs in more detail. In the summer of 1988, the selection was limited to two designs. In the end, the design with the “floating sector door barrier” became the favorite. On 27 October 1989, the agreement was signed for the design, the construction and five years of maintenance. See Figure 3.

Figure 2

Main barrier (dikes)

Figure 3

Floating sector door barrier in closed situation

Source: Directorate-General for Public Works and Water Management

Main barrier, part of Delta Plan being implemented Main barrier, part of Delta Plan to be improved

Main barrier, improved part of Delta Plan

3

Purpose of the Barrier

Main purpose of the Barrier is to lower the water level in the areas behind it.

reducing effect This effect diminishes inland with increasing distance to the barrier. Generally,

the water level of the sea has the greatest impact in the area from the coast up to the town of Dordrecht, the estuarine region. Timely closure of the Maeslant Barrier produces a reduction at Rotterdam of at least 1.25 meter relative to the reference datum. The reference datum (also called Hydraulic Boundary

Conditions or HBC) is a statistic parameter. It is the water level that is exceeded once every 10,000 years, on average. Components of primary barriers, such as dikes and civil engineering works, are designed for this reference datum. This particular frequency, of once every 10,000 years, applies to Rotterdam and surroundings. For Dordrecht, it is once every 2,000 years. Even in Dordrecht, the decrease of the level will still be approximately 0.35 meter. Close to the town of Gorinchem, the effect will barely be noticeable; river flow is the main factor there.

sea level rise A potential sea level rise was also taken into account during the construction of

the Barrier. At the time of the design, that was approximately 25 cm every 50 years. The barrier has led to a drastic reduction of the efforts to strengthen the dikes in the entire region. See Figure 4.

Figure 4

4

The six designs

The five contractor consortiums created six designs. The Commission examined the submitted designs.

In two of the designs, the water-halting elements were located on the riverbed. The water-halting elements were flaps that were pushed upward hydraulically or pneumatically (see Figures 5a and 5b). The third design, the sliding-door barrier, consisted of two giant rolling doors (see Figure 5c). The other solution was a so-called boat door (see Figure 5d).

sector door barrier The two other contractor combinations suggested a “segment door barrier” and a

“sector door barrier”. In these cases, the barrier consisted of two sectors, carried out as water-halting doors (see Figure 5e). The first one moves into the river on rails, hence only moves horizontally. The other one floats into the river, and is then sunken onto a concrete sill.

The design with the floating sector doors became the favorite. This moving sector door barrier by Bouwcombinatie MaeslantKering (BMK) consists of two hollow tubes or casings (the retaining walls), which form part of a circle (50/360 of a circle). These retaining walls are connected to a hinging point (the joint) on each of the banks by means of steel arms (the lattice arms). The combination of retaining wall, lattice arms and joint is also called “door” or “sector door”.

sediments A major advantage over the other designs is that there is no deposition of silt and

sand (sediments). During sinking, a large flow velocity develops under the doors. As a result, silt deposits on the sill will be washed away. If necessary, the doors can land on any remaining sediment. This layer may even be between 1 and 2 meters thick.

Principe drawing (side-view) a.

Principe drawing (side-view) b.

Principe drawing (top-view) c.

Principe drawing (top-view) d.

Principe drawing (top-view) e.

Figure 5

a. Pneumatic barrier b. Hydraulic barrier c. Sliding-door barrier d. Boat door barrier

e. Segment door barrier/sector door barrier

docks The doors are parked in docks. Moreover, it is possible to carry out maintenance

to the doors after pumping out these parking docks. The dock does not need to be very deep, as sinking takes place in the river itself.

5

Performance

5.1 Design and construction

The Directorate-General for Public Works and Water Management drew up the following boundary conditions in the late 1980s, with as main objective to lower the normative high-tide levels (test levels):

 probability of failure less than once every 1,000,000 years;

 probability of failure to close or halt water less than once per every 1,000 requests to close;

 probability of failure to open after a closure: 1 in 10,000 times of opening requests;

 passage width must be minimally 360 meters;

 the unobstructed draught must be 17 meters below Amsterdam Ordnance Datum; passage for shipping traffic on the river must be unimpeded during construction of the barrier;

 maximum time to close two-and-a-half hours;

 maximum time to open two-and-a-half hours;

 life of non-replaceable parts at least 100 years;

 the Barrier has to be able to drain (discharge water from the river). Note: The requirements regarding probability of failure were adjusted later. The passage width measures 360 meters between the land abutments.

passage width This is the nautical passage width of the New Waterway. Slightly beyond the

Barrier, that nautical passage width is also 360 meters, as measured between the groins. See Figure 6.

Figure 6

The Maeslant Barrier in opened position

Source: Directorate-General for Public Works and Water Management

draught The unobstructed draught at the site of the barrier is approximately 17 meters

below Amsterdam Ordnance Datum, over a passage width of approximately 318 meters. The surface at 17 meters below Amsterdam Ordnance Datum consists of concrete sill blocks. These are the supports in the river, for the barrier.

With a view to a possible future deepening of the waterway, the sill lies lower than the present draught on either side of the barrier, which is 15 meters under Amsterdam Ordnance Datum.

10 meter 21 meter rubble 17 meter 10 meter 21 meter rubble Combiwall Combiwall

This is a cross-section. The 17-meter section consists of sill blocks. The sloping part is made up of rubble with a top layer of boulders weighing between 10 and 15 tons each.

No suspension of shipping occurred during the construction of the barrier. During the construction of the sill, the navigation channel was divided into corridors; these were temporary constrictions of the passage width.

When closing the Maeslant Barrier coincides with excessive river discharge, it has to be possible to drain this river water.

drainage This, of course, is only possible when the water level in the river between two

high-tides is higher than the water level of the sea. In this period, water can be drained by letting the barrier float.

5.2 Period 1997 - 2004

Bouwcombinatie (BMK) In May 1997, the builder – BMK – delivered the Maeslant Barrier to its client,

the Directorate-General for Public Works and Water Management, after which the Zuid-Holland division took over the Barrier’s management.

In May 1997, the official Royal closure and delivery took place. As of 1998, an annual so-called performance closure has been carried out. The first closures revealed that the barrier still had teething troubles of such a nature that the barrier would never be able to function as envisioned in the design, without drastic measures. In addition, after the performance closure of the year 2000, the ball joint on the South side turned out to be damaged.

design philosophy One assumption in the design philosophy was that the Barrier’s closure and

opening has to be fully automated. In principle, human action is undesirable so as to avoid human error. Manning the Barrier during a storm surge closure,

therefore, is not required. The objective of having staff present on the site in spite of that is to create a backup for the contingency that the Barrier fails. The term “fail” is used here to indicate the event that the barrier does not close fully automatically when it should.

performance closures A new analysis based on conducted performance closures, among other things,

revealed that the probability of failure was greater than assumed in the design (namely, a probability of 10-3/request to close and a probability of

360 meter

10-4/request to open again). As a response to these findings, a large number of actions were undertaken that resulted in a reduction of the Barrier’s failure probability to an acceptable level. On the basis of further analysis, the

requirement with respect to the probability of failure to close could be reduced to 10-2/request (“1 per 100”). The requirement with regard to failure to open is less important for high-tide flooding protection.

The causes of the problems predominantly stemmed from the following five issues:

 not enough equipment to control the barrier with the focus on the probability of failure;

 quality and size of the organization charged with management;

 knowledge of the system and preserving it within the organization;

 adjustments in the area of among other things, fire, lightning strikes and related failure;

 insufficient reliability of the software, notably of the control system BES (BEsturingsSysteem) and, to a lesser degree, of the decision and support system BOS (Beslis- en Ondersteunend Systeem). The BES carries out the commands given by the BOS (see Section 7.1).

These five problem areas have been resolved.

5.3 Period 2005 – 2009

The period 2005 to 2009 was characterized by the introduction of Probabilistic

ProBO Management and Maintenance (ProBO).

Water Act Within the framework of the Water Act, previously called Flood Defenses Act,

derived requirements with regard to probability of failure were set for the flood defenses. Requirement for the Maeslant Barrier is a failure probability of 1 in 100. That means that the barrier is only allowed to fail once per every 100 times it is supposed to halt water. The probability of failure performance is 1 in 109 (as determined in October 2011) and is therefore in compliance with the Water Act. Essence of the ProBO is a demonstrable coupling between the probability-of-failure requirements and the way in which management and maintenance are carried out. The necessary management and maintenance are derived from the probability-of-failure requirements. Experiences gained during management and maintenance are used to check whether the probability-of-failure requirements are still met. If necessary, management and maintenance are then adjusted on the basis of the experiences. Management and maintenance, and the probability-of-failure requirements are therefore constantly coupled

Plan-Do-Check-Act via a ProBO cycle, which can be seen as a Plan-Do-Check-Act cycle.

1. drawing up maintenance plan 2. carrying out maintenance plan 3. monitoring performance 4. management of failure probability

failure probability Calculation of failure probability (risk analysis)

Coupling between the failure probability requirements at the highest level (probability of not closing or not opening per request to close) and requirements of management and maintenance is achieved by means of an extensive risk analysis. This risk analysis is documented in a so-called fault tree. In the fault tree, all components and systems (including the human element) of the flood barrier are modeled with their associated failure behavior and assumptions regarding technical quality, as well as management and maintenance. An important component of ProBO is continuous updating of this fault tree.

In 2003, the calculated failure probability was approximately 1 in 10. Since then, an upward trend was started, so that as of 2009, the failure probability

requirements are amply met. The basis for this upward trend is a series of improvements to technology, organization and staffing.

5.4 Verification closure (November 2007)

storm conditions The Maeslant Barrier was first closed in (near-) storm conditions on 8 and 9

November 2007. In 2006, the Horvat & Partners consultancy recommended testing the Maeslant Barrier not only in good-weather conditions but also in heavier weather. Only then could the barrier’s robustness truly be demonstrated. The Barrier normally closes at a predicted water level at Rotterdam of 3.00 m + Amsterdam Ordnance Datum. The probability of closure is not very large (on average, once every 7 to 10 years). That is why in 2007, the decision was made in to lower the closure level to 2.60 m +Amsterdam Ordnance Datum

temporarily. That level was already reached less than six weeks into the storm season. The barrier came in action on the basis of a predicted level at Rotterdam of 2.84 m +Amsterdam Ordnance Datum. This closure at a lower closure level is called verification closure (the design is actually verified in practice).

A special measurements program was carried out during this closure to collect as many data as possible.

Fail ure pro pbab il it y per re ques t [1 t o …]

An important conclusion was that the barrier was subjected to a differential head (drop) of a similar size as occurs during a real storm closure and that the barrier closed successfully in those circumstances. It was established that all components of the barrier met all of the still valid assumptions of the design with regard to loads and displacements.

The figure below shows the water levels during the verification closure of 2007.

riverside seaside

fatigue damage The measurements also confirmed that conducting performance closures only

causes a small amount of fatigue damage to the Barrier’s components. A performance closure gives, albeit at a somewhat lower differential head, just as much insight into the behavior of components of the barrier as a verification closure. Major difference is that the dynamics resulting from wind and waves are almost absent during a performance closure.

The verification closure provided valuable results. Many questions were answered; other questions will still remain a topic of investigation for a little while. The installed measurement systems play a very important role in this investigation.

6

Location and Europort Barrier

The Maeslant Barrier was projected near the mouth of the New Waterway, between kilometer marks 1,026 and 1,027. The Maeslant Barrier is the most important component of the entire line of defense that runs through the Europort.

line of defense The industrial areas Europort and Maasvlakte were created at a level of

approximately 5 meters above Amsterdam Ordnance Datum. During an

extremely high storm surge, any surplus of water can still flow toward the lower areas further inland.

Europort Barrier That is why the Europort Barrier is needed. See Figure 7.

Figure 7 Europort barrier

The Europort barrier starts on the Rozenburg spit, adjoining the South side

Hartel Canal of the Maeslant Barrier. On the map, this water barrier runs toward the Hartel

Barrier in the Hartel Canal, which was constructed to the west of the town of Spijkenisse. This second storm surge barrier is needed because the Beer Dam – on the left in Figure 7 – south of the Maasvlakte, was breached in 1997. That created the possibility of a shipping channel for inland shipping.

Beer Dam The water-halting function of the Beer Dam was therefore abolished and the

described Europort Barrier, of which the Hartel Barrier is an element, took over de Beer Dam’s role.

6.1 Hartel Barrier

The Hartel Barrier (SSBHC) is of the “lifting-sliding type”: Two gates are suspended between four towers. Halting of water takes place by lowering these panels onto a concrete sill in the canal. At extremely high water levels, about 3 meters above NAP, this barrier will allow water to overflow. This will, however, never be that much that it will hamper the performance of the closed Maeslant Barrier. The inland effect (approximately 200 km2 water storage) of the

overflowing water is limited, as it would take too long for any rise to take place. See Figure 8: Details of operating principles of the Hartel Barrier are described in document HA-21-15, “Operation of Hartel Barrier”.

Figure 8 Hartel Barrier

7

The halting process of the Maeslant Barrier

7.1 The principle of the Barrier

The brain behind the Maeslant Barrier is a high-quality computer called the Decision and Support System or BOS.

This system decides whether to close or not to close, and is fully automated, which diminishes the probability of human failure.

BOS The actual and expected water levels, wind data and river discharges serve as

basis for the BOS. This computer does not only make the decisions for the Maeslant Barrier, but also for the Hartel Barrier. In the event of a closure, the BOS sends commands to the Control System Maeslant Barrier (BesW) and the Control System Hartel Barrier (BesH).

BesW The BOS decides whether to close or not to close on the basis of measurements

and predictions and subsequently controls the resulting main processes. The BesW and BesH then carry out the commands of the BOS.

closure level The Maeslant Barrier is closed at an expected water level of 3.00 m +Ordnance

level at Rotterdam or 2.90 m + Ordnance level at Dordrecht. If one of these levels is exceeded, the BOS system is activated pursuant to the procedure (see 7.3).

Before the Barrier can close, the water level in the docks must already have been made equal to the water level in the river; this is done by using the dock gates. It causes the sector doors to float. At a water level of approximately 1.30 meter below Ordnance level, the sector doors lift off from their supports. The gates to the parking docks, the dock doors, are opened when the water levels of dock and river are equal. The moment that the doors start to depart from the docks depends on the type of closure.

horizontal movement The horizontal movement (travel) of the floating sector doors starts. The drive

mechanisms (the “locomobiles”) on both sides push the sector doors to the middle of the river in thirty minutes’ time. Once arrived there, sinking can start.

vertical movement Valves are opened in the submerged part of the Retaining Wall. The vertical

movement (the sinking) takes a little over an hour. Opening the barrier again takes place as follows. Lifting the sector doors, by pumping the water out, takes approximately ninety minutes. Next, the locomobiles pull the sector doors – now floating again – back into the docks. Subsequently, the dock gates are closed. See Figure 9.

1. abutment 2. parking dock 3. ball joint & joint foundation 4. threshold 5. lattice arms 6. barrier 7. motion machinery 8. operations building 9. dock door Figure 9

7.2 Development of the water levels

Figure 10 displays two possible development scenarios for a storm. The time in hours is shown on the horizontal axis. The vertical axis represents the water level in meters relative to NAP (Ordnance Datum).

Figure 10b shows that the normal tidal cycle runs from 0.6 meters below NAP to approximately 1.10 meter above NAP and back. Such a cycle takes 12.5 hours, as can be seen on the horizontal time line.

Time T (hours)

1. Prepare closure 2. Closure 3. Open & rounding

Inner water level Return

Barrier in wait position Floating

Barrier sunk

Departure Shipping suspended

Call-up staff

Equalizing docks/ shipping suspension request

Initial warning W a te r le v e l (m + N A P )

Expected moment of closing (T=0)

Note: times are in black depending on water movement

Figure 10a Storm graph

A storm surge changes the situation completely. The increasing water level in the North Sea causes a great deal of water to flow into the New Waterway. Figure 10a shows that the “supply” from the sea is 2.5 meters more than during a normal high tide.

setup This increased rise of the level is called “wind setup”. In the storm graph of

Figure 10a, this is visible in the increasing water levels. In this situation, the Barrier closes at a water level of 2 meters above NAP, also called a 2+ closure. Closing relatively late limits the differential head across the barrier. The lower line indicates the evolution of the water level on the inland side of the barrier.

discharge The discharge (the flow) of the river – in this case 2,200 m3/s –continues. As a

result, the water level on the inside rises gradually. The average discharge of the Rhine River is 2,200 m3/s, as measured at Lobith. The Meuse River also supplies water, but at a much lower average of approximately 250 m3/s.

The inland water level – in other words, the level behind the closed barrier – shows some variation, after which it increases again, as represented by the solid rising line.

translation wave This variation is the result of the occurrence of a water fluctuation called

translational wave. A translational wave develops when the moving water is stopped by what is essentially a closed valve (the barrier) and is partly reflected, as a result of which the level rises at the front. At the back, a decrease develops. Over time, the water returns by reflection via the port basins.

After all, the water will continue to build up behind the barrier for a while until it flows back and fills up the newly formed depression. The decrease is the effect of

the flowing water’s inertia, and of the prevailing wind, which is very strong, and blowing from the northwest. It whips up the river water level behind the closed barrier in the direction of Rotterdam.

storm peak In Figure 10a, the storm setup lasts approximately 32 hours, from hour -10 to

hour +22. During that time, the inland water level is lower than the seaside water level. As the average river discharge in such a storm situation is 2,200 m3/s, the water level in the closed off river area remains within bounds.

After the storm, the seaside water level subsides to the normal level within hours (reached at hour 7), and the barrier can be opened.

The storm graph in Figure 10b shows a different storm. In this case, the setup above average high tide is also 2.5 meter. The discharge of the river as measured at Lobith is substantial, namely 6,000 m3/s. The two-peak storm lasts about 40 hours. Between the two high tides, a considerable decrease in the water level occurs on the sea side.

At the mentioned large discharge of the river (6,000 m3/s), a detrimental situation will develop for the Maeslant Barrier. In this example, the river water level is temporarily (between the two storm peaks) higher than the level on the seaward side. This means that the forces acting on the barrier come from the opposite direction and from that direction, the barrier can only absorb a limited stress (maximum water level difference of 1.50 meter).

In this situation, the barrier will have to be opened temporarily, for two reasons: 1. River water is halted, which means that there is a negative differential

head across the barrier (river water level higher than level on sea side). 2. Notably at Dordrecht, the water level can become too high. In this

situation, river water has to be drained between the two storm peaks. This is done by letting the barrier float temporarily.

Figure 10b Storm graph W a te r le v e l in m e te r re la ti v e t o N A P Setup = 2.5 meter Discharge = 1000 m3/sec time in hours

sunk draining sunk

low and high tide

6000

AO

Even more extreme scenarios are possible. If the river discharge is more than 6,000 m3/s, the Maeslant Barrier will close earlier, namely when the low tide changes into high tide. This is called a turn closure, referring to the turning of the tides. The advantage of a turn closure is that as much water from the sea as possible is held back.

The storage capacity of the estuary is then fully available for the river’s large discharge. In other words, the incoming storm surge is largely kept outside. The retaining walls need to have enough freeboard in order to be able to depart from the docks so as to avoid collisions with parts of the docks. The command to depart will only be given when a sufficiently large gap size is reached.

These are only two examples of storm situations, but many combinations of setup and discharge are possible. Such combinations are caused by the tides, the wind effect and the river’s discharge.

seiche Seiches are a phenomenon that was initially underestimated. The Dutch Van Dale

dictionary defines a seiche as follows:

 Seiches (pl.) [Fr.], (geol.) periodic level changes in lakes or almost landlocked ports (as a result of changes in air pressure).

For a long time, the generating mechanism behind water fluctuations at sea (also called long sea waves) was not understood. Martijn de Jong put an end to that in 2004 (reference: 2004, PhD thesis Martijn de Jong; Origin and Prediction of Seiches in Rotterdam Harbour Basins). He discovered that seiches are

predominantly caused by convection cells in the atmosphere. These cells develop almost exclusively in strong northeasterly winds. The work of Martijn de Jong has made it possible to predict the occurrence of seiches. These predictions have now become a component of the weather forecasts. Predicting the size of a seiche is still difficult, however.

The North Sea has water fluctuations with periods ranging between five and ninety minutes. In the port basin, these fluctuations swing up higher. A port basin can be seen as an organ pipe. If the pipe is hit at the right frequency, the

fluctuations can increase greatly. In the Netherlands, this phenomenon leads to significant values. IJmuiden and Rozenburg have peak-to-valley values of more than a meter in a short time.

That the effects of a seiche on a negative differential head were much greater than initially assumed only became clear in a relatively late stage of the design. For when the barrier lifts, a design value of approximately two meters

(amplitude) had to be taken into account. It was impossible for the joint to absorb the resulting negative differential head loading. An extensive investigation followed (A-14-0021; Umbrella Document Seiches). The solution was so-called dynamic pre-stress management. By measuring the differential head continuously and adjusting the ballast accordingly, it is possible to lift almost immediately when the water levels have become equal. Any developing differential head can then rapidly flow away.

The size of a seiche at the Maeslant Barrier is a function of the layout of the harbor basin. A change in the geometry can impact this. This is why the geometry of Maasvlakte 2 was tested extensively. Fortunately, it revealed that

Barrier. In the future, changes to the geometry and adjustments of constructions (for example the degree of perforation of the Noorder Dam) in the port area must be tested the same way.

7.3 The halting procedure

See also the captions on the time line in Figure 10.

The moment indicated as 0 hours in Figure 10a is the time of actual closure (start of travel of retaining wall into the river).

call-up operational team The operational phases for a storm closure are briefly described below. A

performance closure is carried out in almost the same manner. The only difference is that the performance closure can be abandoned.

The main operational phase is divided into four phases:

Phase 1: mobilization, the Operational Team has been called up. Phase 2: alert, the Port Control Center (HCC) is aware of the expected

suspension of traffic and the closure.

Phase 3: readiness, the HCC has stopped all shipping.

The shipping signaling has been activated. The barrier is ready for closure; the distinction is made between a level (2+) closure and a turn closure.

Phase 4: maneuvering occurs in the following sub-phases;

 horizontal closure;

 sinking;

 sediment stop (if required);

 halting;

 floating;

 draining;

 waiting for a sufficiently large gap;

 horizontal opening.

normal closure procedure In a normal closure procedure, this entire procedure schematically takes place as

follows:

– 20 hours : an alert goes out to call up the Operational Team to the control center if the forecasts are for more than 2.60 meter +Ordnance Datum at Rotterdam and/or 2.30 +Ordnance Datum at

Dordrecht;

– 8 hours : the announcement is made that shipping will be suspended. – 4 hours : the water level in the docks is equalized (making water level in

parking docks equal to the water level of the river; this is done by opening the gates in the dock doors), the dock doors are opened, and river traffic is suspended immediately thereafter. – 2 hours : shipping is suspended in the New Waterway and the Hartel

Canal;

– 0 hours : the sector doors start to depart from the docks.

± 0.5 hours: the travel of the sector doors is completed, and sinking starts. ± 1.5 hours: the sinking of the sector doors is completed, and the Maeslant

Barrier is closed; the amount of ballast in the compartments depends on the size of the differential head.

After the storm peak, at equal water levels in front of and behind the barrier, the

Opening procedure opening procedure is started; opening is beginning at 0 hours (7 hours in Figure

10a).

+ 0 hours: ballast is removed from the retaining walls.

+ 1.5 hours: the sector doors are floating, and the decision is made to drain or return to the docks. This is also when the phase starts of waiting for a large enough gap. It means that horizontal opening of the barrier does not take place until there is a large enough gap to be able to return the doors;

draining usually takes place when a second peak in the water level is expected. The retaining walls start to return to the docks. + 2 hours: the return to the docks is completed, and the dock doors and

dock gates start to close. Shipping can be resumed. The water level in the parking dock is lowered to the resting level (control water level). The barrier transitions from the “operational” stage to the “rest” (or “wait”) stage.

In a normal situation, the entire closure is controlled by the decision and support system (BOS). This system is located in control center North.

See Figure 11.

Figure 11

Control center North Maeslant Barrier

Summary

The Maeslant Barrier is an alternative for further raising of dikes, which would have major consequences, notably in urban areas. The storm surge barriers in the New Waterway and the Hartel Canal link up with the Europort Barrier and are part of the Delta Plan. The Maeslant Barrier has a reducing effect on the water level in the estuary. The Maeslant Barrier is of the type “floating sector door barrier” and was selected by the Commission Storm Surge Barrier New Waterway from six designs. The Maeslant Barrier had to meet various requirements, of which one of the most important ones is the requirement regarding the probability of failure. The design and construction are fully in accordance.

Barrier operation takes place in a series of steps, of which the horizontal and vertical movements (sinking and lifting) are the main stages.

Two storm graphs were used to help explain how the halting process works out for certain seawater levels and river discharges. Attention was also paid to the seiche phenomenon.

Whenever the water level exceeds the closure level, a predetermined schedule of procedures is carried out.