IABR2012 Where beavers and seals meet

Haringvliet-Hollandsch Diep

4 Where beavers and seals meet Bosch Slabbers Landscape Architects

The Haringvliet-Hollandsch Diep-Biesbosch area encompasses the complete estuary from Voordelta to Biesbosch. This is an area where the influence of the sea and the rivers combines, where fresh water and salt water meet. It is an area of contrasts: idyllic villages and towns next to vast rural polders, the Moerdijk high tech petrochemical industry next to mud flats and salt marshes, peace next to vitality and dynamism.

Bureau Bosch Slabbers explored the flood risk management issues for this area and has developed a number of future scenarios.

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Delta Programme

Construction of the Haringvliet dam has dispelled all threat from the sea. The dikes along the Haringvliet and Hollandsch Diep need now only keep the river water at bay. At times when high river levels occur simultaneously with a heavy storm at sea (and the Haringvlietsluizen sluices, Maeslantkering dam and the Hartelkering flood gates are closed), the river water is temporarily stored in Haringvliet and Hollandsch Diep. This means that water levels there can rise considerably.

As the base sea level is rising, the dams will need to be closed more frequently and for longer periods of time causing the normative high river levels to rise.

As a result more water will need to be stored in the future.

No serious issues are expected in the short term (until 2030). Most of the dikes along the Hollandsch Diep-Haringvliet are strong enough, and where that is not the case they can relatively easily be reinforced. From a technical point of view the tried and tested strategy of ‘reinforcing the dike’ will be sufficient for a long time yet. The flood risk management for the short term is therefore relatively simple and can be cheaply solved using standard engineering techniques. This may make the area safer, but it will not necessarily make it any more interesting.

The real task is to devise solutions that will not only make the area safer, but will make it a more interesting place in which to live, work and stay and will improve the ecological quality. In other words solutions that not only work but also have added value.

Increasing the storage capacity In the long term (from 2030) however the storage capacity must be increased. There are three options.

Option one: raising the water table by raising the

dikes along the Hollandsch Diep and the Haringvliet. Option two: draining water into the Volkerak-Zoommeer lake and the Grevelingen, thereby reducing the normative high-water levels of the Haringvliet by 40cm. This option would postpone (by about 30 years) the need to reinforce the dikes along Hollandsch Diep and Haringvliet and would mean that the eventual reinforcement would be less major. Option three: increase the surface of the storage plains by relocating the dike.

To achieve this, the current primary dam would be lowered for much of its trajectory and a new dam would be constructed land inwards.

Option1: making the storage basin deeper

Option2: adding an extra storage basin

Option 3: making the storage basin wider

This study explores the first and the third options: see the information box ‘Super dike versus dike relocation’.

Eliminate weaknesses Ideally the measures used for the flood risk management and to preserve the fresh water supply should go hand in hand with eliminating the negative aspects of this beautiful area. Aspects that need improving include: • The contact zone between the land and the water has been reduced to a rigid coastline. There are

Rhine-Meuse Delta, opportunities for the current flood risk management strategy in 2100

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few inter-tidal areas and those that are there are threatened by the rising water levels. These mud flats, salt marshes and shallows are however essential to linking the Voordelta with the Biesbosch. They encompass the gradual transition from land to water with a continuous process of silting up and erosion. The lack of an intertidal area distorts the relationship between the Voordelta and the Biesbosch.

• Where traditionally life was focussed on and around the water, the focus now is away from the water. In addition to its function as dam, dikes were also used for ribbon development; a raised route along the water and a collective catwalk along the transition between land and water.

However, after reinforcement, the dike has reverted to being a barrier between the water and the life behind the dike rather than a link connecting the two. The dike is increasingly becoming a ‘fence’ behind which the landscape, the villages and the cities shelter.

• The relationship with the South Wing is limited, both in functional and economic terms. The Haringvliet-Hollandsch Diep-Biesbosch area is thought of as the ‘far side of the Randstad’ rather than being the ‘gateway to the delta’. Rotterdam is more often thought of as a city on the river than a city on the delta. Over recent years the city’s relationship with the river Maas have been strengthened, but no attention has been paid to its relationship with the delta.

Desirable situation in 2100

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Delta Programme

• Private investment in nature and recreation in the area has been limited and is considerably less than the private investment in Zeeuws Vlaanderen or along the Grevelingen. The closer to the South Wing, the less private interest.

Wishes for 2100 In 2100 the dikes will be expected to play a key role.

Everything converges on the dike. The dike keeps the water at bay, guarantees safety and security and links the land to the water. Areas of natural interest develop along the dike, people live and spend leisure time on the dike and invest in it. The dike is no longer mono-functional but is part of a multi-functional dike landscape.

In 2100 the Hollandsch Diep-Haringvliet has developed into a lively, green gateway to Rotterdam, into a diverse landscape. Easy access from the city centre enables the gateway to the city to flourish: attractive and pleasantly laid out interwoven routes (by foot, bicycle, horse, car, public-transport or boat) link the Coolsingel with the Rotterdam Coffee House on Tiengemeten Island. Along the water, the ‘Grote Deltazoom’, with its new forms of housing and recreation, has arisen. Private parties invest in the landscape. The delta can be experienced everywhere; land and water are interwoven.

Consider the area from the Voordelta to Biesbosch: in 2100 this has become a continuous nature reserve known as ‘the Blauwe Loper’ (the Blue Runner). The structure of the estuary is clearly visible with the

water purification in the dunes beach and surf

Dune Dike

seals

living in the dunes

dynamic broad barrier with woods and sand dunes

Super dike versus dike relocation In the long-term it is essential that the storage capacity of the Haringvliet and the Hollandsch Diep is increased. What will the area look like if the dikes are raised?

Option: super dike The dikes on the north bank of the Haringvliet and the Hollandsch Diep will be raised and widened to form a plateau. Together with the bordering foreshores and surrounding countryside this will create a dike landscape with a wealth of opportunities. Three types of dikes can be distinguished: 1. Dune Dike. The dike to the west of Hellevoetsluis will be reinforced using extra sand. This will create a wide, dynamic dike with woodland and sand dunes and space for a range of programmes.

2. Marsh dike. The dike around the mouth of the river Spui will be reinforced using clay and sand, obtained by scraping and lowering the foreshores. Lowering the foreshores will return the area to the tide’s influence and the marshes and mud flats will once again be regularly submerged at high tide. The marshes and mud flats help protect the dam: they dampen the wave action and increase the stability of the dam.

3. Biesbosch dike. In the eastern part of the area, the dike will be reinforced using dredging obtained from the shipping channel. Tidal forests will develop on and in front of the dike, linking in with the Biesbosch system. In additional to ecological value, these tidal forests also help protect the dam; they too dampen the effects of the waves.

And what will it look like if the dikes are relocated inland?

Option: dike relocation Along the north banks of the Haringvliet and the Hollandsch Diep a new dike, 25km in length, will be constructed land inwards. The existing dike will be lowered to a level that will regularly flood. This will increase the outer-dike waterstorage area by 30 km2.

Relocating the dike will mean that some towns and villages are once again situated at the waters edge. New, stately water facades will be developed, rising out of the dike like bastions. The area between the dikes will gradually be transformed into a wet and rugged delta wilderness. Within this zone there will be room for the development of new (part-time) housing and more innovative forms of tourism and residential recreation.

In the eastern part, tidal forests will grow in the new outer-dike areas. The new lower lying outer-dike polders around the mouth of the river Spui will be transformed into marshes and mud flats. A dune valley will arise in the new outer-dike area to the West of Hellevoetsluis, forming part of the silted coast.

delta estates

dike becomes part of the supplemented sand dunes

sand extraction in the delta coast (possibly coupled with extraction of masonry sand)

Marsh Dike

summer cities salt marshes and mud flats

marinas self-sufficient living

dike becomes wider and it’s profile more differentiated

scraping away the higher fore-lands returns the land to the tide and also provides soil

Biesbosch Dike Living in the woods tidal flood forests beavers and otters living in the marshes

canoes and silent boats

making use of dredging slush to create a wide dike, purification by the Biesbosch flora (reeds, willows etc)

fresh water tidal nature

maintain depth of downriver navigation channel

sequence from fresh water through brackish to salt water. The nature reserve ‘The Hoge Veluwe of the Delta’ is unique in Europe, the place where seals and beavers meet.

The development of salt marshes and mud flats increases the inter-tidal environment. More of the Biesbosch becomes tidal whereby the total fresh water tidal-area also increases and new tidal forests are created.

Improved relationship between land and water In 2100 the towns and villages have strengthened their relationship with the water by restoring old harbour canals and developing new waterfronts. At Voorne and in the Hoeksche Waard the inner-dike system of creeks and streams has been extended.

This has improved the water balance in the area (local fresh water buffer and agriculture, local water storage) and forms an unbroken network of navigation channels. The dike has once more become the lifeline of the area, the element linking land and water.

In 2100 the people of Rotterdam have discovered that the delta has much more to offer than just being a boring Green Hart. From the increasingly warm city, the urban dwellers look to the delta for cooling, both on and around the delta waters.

Rhine-Meuse Delta, opportunities for the current flood risk management strategy in 2100

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Super dike

archipelago

dune dike Delta Metro mixing bowl fresh and salt water

green routes to the city

delta estates A4-A29

rejuvenate streams and canals

Happy Coast; spending leisure time on the dike

lowered salt marshes

historical harbour centres water taxi

the Tiengemeten delta experience

new waterfronts Rotterdam’s Coffee House

living in the dunes

for gentle recreational use

Super dike DUNE DIKE 58

Delta Programme

super dune as wide flood barrier

dune bastion Hellevoetsluis

Hellevoetsluis beach

recreation on the Haringvliet water

Haringvliet and self-sufficient outer-dike mud flats homes on stilts

Super dike SALT MARSH DIKE

Marinas emerge and expand, as do new forms of country living and holiday resorts. Summer towns and country houses arise along the banks of the Haringvliet-Hollandsch Diep.

Dordt’s Coffee House

Rott erdam Port Barons

water taxi Dordrecht on the Biesbosch

In 2100 private parties have discovered the multitude of opportunities in this area within an hours drive of Rotterdam. The area has been re-created by the new generation of ‘Port Barons’; they invested in the quality of the living environment by setting up a number of delta estates, summer towns and marina cities. Not only for their own enjoyment or to make money, but also because an attractive living environment is essential if high-quality personnel and other businesses are to be attracted to the area.

The previous comparison with the Hoge Veluwe is more just than a coincidence. The Hoge Veluwe National Park was built using capital provided by port barons. The Kröller-Müller family established their hunting territory there and built the hunting lodge and museum. Furthermore it was the port barons of Rotterdam who constructed a tramline which transformed the agricultural village of Wassenaar into a residential suburb. In 2100 something similar is happening with investments in Delta estates on the banks of Hollandsch Diep and Haringvliet.

living in the woods

living in the Biesbosch

Uncertainties for 2100 So much is uncertain, who knows whether these wishes for the future will ever be feasible? How will the demography and the economy develop? How long will the current recession continue and will this be followed by period of boom? It appears that the Randstad will be able to avoid economic recession until at least 2030. After that predictions are uncertain. The future views that have been

tidal forests

outer-dike Biesbosch summer city on the water

super dike with residential landscape on the higher land

Hoeksche Waard floodplains

canoes, beaver lodges and silent boats

houses on stilts dredging sludge depot converted into Biesbosch residential area

observation centre

Biesbosch backpack track

Super dike BIESBOSCH DIKE Rhine-Meuse Delta, opportunities for the current flood risk management strategy in 2100

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Dike Relocation

water taxi slow routes to the city new streams and canals

archipelago

Delta Metro

dune villages

slow routes to the city

new waterfronts mixing bowl for fresh and salt water

dune valley A4-A29

living on the mud flats

Marina City

expansion of the salt marshes Hellevoetsluis waterfront

historical harbour centres relocated new dike Groot Tiengemeten Island Delta Experience

historical harbour centres

Rotterdam’s Coffee House water taxi

gentle recreational use living on the relocated dunes

Dike relocated SILTED COAST 60

Delta Programme

new urban fringe bastion Haringvliet along the dune valley Nieuw-Hellevoetsluis dune valley lightly-tidal sea historical inlet environment Hellevoetsluis

former dike as development axis

marina HaringvlietHollandsch Diep

living on an island

Dike relocated SALT MARSH AND MUD FLAT ENVIRONMENT

Dordt’s Coffee House watertaxi Dordrecht on the Biesbosch

living in the woods

tidal forests

expansion of the Biesbosch system

Hollandsch Diep advanced bastion for a range of functions summer city linked to the former dike flexible polders

current village

sketched in this article are based on a period of boom: in 2100 the Netherlands and the South Wing are booming. Voorne-Putten and the Hoekse Waard are of considerable economic value, continuation of the current levels of flood protection is essential.

In 2100 all the dikes meet safety standards. In and around the Port of Rotterdam plenty of money is being earned. This is being invested in the gateway to Rotterdam.

However, what happens if instead there is a period of recession and the population of the Randstad shrinks significantly? How do we tackle flood risk management and invest in the quality of the living environment? In the case of recession, the flood risk management can be approached in two different ways.

One: if the economic value of the land behind the dike becomes less, then lower standards will apply (from 1:4000 to 1:2000). Large-scale interventions to raise and reinforce the dike will no longer be necessary leading to savings in expenditure. Two: Along the Haringvliet and Hollandsch Diep there is sufficient room for the dike to be raised and reinforced relatively simply and inexpensively.

Maintaining the standards for safety and security are rapidly cost effective and affordable even during a recession.

During a recession the Port of Rotterdam will no longer bring in vast sums of money; the time of large-scale private and public investment in the living environment is gone. However, the slump does mean that the value of land will plummet making the purchase of one hectare of land well within the means of a large group of people.

Depending on the role that the government chooses to take, the gateway to Rotterdam may revert to a ‘free state’ with developments taking place on an individual basis.

flexible polders living on an island

houses on stilts

canoes, beaver lodges and silent boats

relocated dike

Rotterdam

Dike relocated TIDAL FOREST ENVIRONMENT Rhine-Meuse Delta, opportunities for the current flood risk management strategy in 2100

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