From Dikes to Mangroves, or Both?

Nature-Based Solutions

Deltares

Traditional interventions are expected to become difficult to sustain under high-end climate scenarios. Natural (BwN) solutions are better able to cope with varying wave conditions and rising sea-levels due to lower energy needs and costs associated to their implementation.

This reality has given rise to efforts to make greater use of ecosystem-based approaches to reduce risks from coastal storms. These approaches draw from the capacity of wetlands, beaches and dunes, biogenic reefs, and other natural features to reduce the impacts of storm surge and waves. In addition to providing engineering functions related to reducing risks from coastal storms, Natural and Nature-Based Features (NNBF) can provide a range of additional ecosystem services, including those supporting coastal ecosystems and communities.

A true systems approach to coastal risk reduction and resilience requires consideration of the full range of functions, services, and benefits produced by coastal projects and NNBF.

Wetland outside a city

[Gentle music] [Gentle music] [Sound of waves] We have to protect ourselves from the water For centuries we have built high dikes But unfortunately this is often at the expense of nature. Recently things have been changing. Our understanding of the water system has improved and we can deal with flood risk in other ways. Hence, we have developed knowledge of building with nature We studied the use of vegetated foreshores for flood risk reduction and the certainties that are needed to implement this system. Such as more knowledge on the precise functioning of the forshores and new forms of governance involving nature conservation agencies and water managers. "So what if we broaden our scope iof we not only consider the water as our enemy but embrace the power of tides and waves in our favor.

Text- flood risk reduction using vegetated foreshores" How could that benefit us. [Music] "Text- Situation without vegetated foreshore In a situation without foreshores there is a high wave load on the dike during storm surges. " "Text- Situation with vegetated foreshore What happens in a situation with foreshores. The systems with mud flats and salt marshes attenuates the waves. Each natural foreshore is characterized by the same gradients. We study the wave damping effect of sediments and vegetation. The wave loads on the dike are lower. The dike can be less high and strong and original nature flourishes." For centuries the sea and rivers have transported small sand and clay particles. These particles are the building blocks of the delta. This natural process is still functioning. However, we fully don't understand how this works exactly. How does the coastal area develop. What causes sedimentation of the particles and under what conditions can new foreshores develop. If we understand the Delta, we can make better use of its natural processes. The vegetation traps sediment during each tide. With the rising sea level new sediment can settle on the foreshore and the foreshore height increases. There is no need for a repeated increase in dike height. In this way, nature can keep developing [Music] We allow centuries-old processes to do the work for us. We build a safe Delta with room for the value of nature which we can keep enjoying. [Music] Text: ecology bio-morphology hydraulics nature preservation governance [Music] Text: flood risk reduction using vegetated offshores [Music] Text- citg.tudelft.nl/be-safe [Music] [Music]

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Muddy Systems

Deltares

Muddy coasts are common around the world. Most are partly vegetated, as these coasts are often sheltered from extreme conditions. Historically, solutions for stabilizing or extending temperate muddy salt marsh coasts have used brushwood groyne systems along tens of kilometres of coastline. Examples are found in the Netherlands along the muddy shores of the Wadden Sea.

Within tropical regions, mangrove belts are very effective stabilizers of muddy coasts. Both systems reduce erosion, can adapt to sea level rise and enable inclusive economic growth, so that coastal communities are safe and can prosper.

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Foreshore Assessment Using Space Technology

Building with Nature for Stable Coastlines in Java

Deltares

There seemed to be no means of stopping the erosion and the floods. Major investments were made in seawalls and wave barriers, but all these efforts failed. Mangrove replanting was not successful as the conditions were not right, such as the input of sufficient sediment. The floods kept creeping further into the village and taking the land by 100 meters every year. People became desperate and made plans to move away, having witnessed neighbouring villages already being swallowed by the sea.

But then a new solution was introduced in the village, called “Building with Nature”. This solution entails the placement of permeable dams (see picture) and was made possible by Wetlands International, Deltares and the Indonesian Ministry of Marine Affairs and Fisheries (MMAF). The permeable dams break the waves and trap sediment, thus reclaiming land. Once the land is back, mangroves can recolonize the area and help protect the coastline against erosion.

Villagers had been waiting impatiently to see evidence of success of this new ‘permeable structure’ approach. This day had come. The waves are much lower inside the grid of permeable dams than outside. In some cases, pioneering mangrove trees are already testing the ground.

A major breakthrough came when the village signed a decree, demarcating 100 hectares of the lost land as protected area. This means that once the mangrove belt is restored, it will not suffer the same fate. The potential and hope is created for a new landscape in which mangroves and aquaculture can be combined sustainably.

Nature based solutions

Nature-based solutions using local resources

Aerial view of wetlands

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Created in partnership with: EcoShape

Sand Engine

Researcher in Deltares

The "sand engine" is a new coastal maintenance strategy designed to use the power of winds, waves and currents to protect part of the Dutch coast while encouraging the development of new dunes and the valuable flora and fauna associated with them.

In this approach, a mega nourishment of 21.5 million m3 of sand was introduced, rising up to 5 meters above mean sea level. The sand is gradually redistributed along the shoreface, beach and dunes by wind, waves and currents. By using natural processes to redistribute the sand, this innovative approach aims to limit the disturbance of local ecosystems, while also providing new areas for nature and more types of recreation.

The Sand Engine is a coastal mega-nourishment pilot project which was constructed in 2011, with the means to improve the efficiency and effectivity of the Dutch coastal nourishment strategy.

Sand Engine located in the Netherlands

Impressions of the Sand Engine

Observed bathymetry August 2012 vs computed bathymetry August 2020

"In 2011, one of the largest sientific experiments in coastal protection took shape in the Netherlands; the sandmotor. [Music] {The Sand Motor- Five years of building with nature} An aritifical peninsula designed to nourish the Delft land coast for the coming 20 years." The sand motor slowly spreads towards the beaches and dunes under the influence of waves, tides and wind. Here nature does its job. Different plants, birds and other animals emerge while nature lovers explore the fascinating and unique coastal landscape of the sandmotor. To plan the realization of the sand motor, financial resources, knowledge, skills and cooperation of all parties involved was essential. For such a large project, it was quite a challenge to get everyone on the same page. Three goals were defined. Contributing to coastal safety, adding an attractive area for leisure activities and nature development and stimulate knowledge development about coastal management. "At the start of this ambitious project, there were only calculated assumptions about what was going to happen in the next couple of years. There were lots of challenges and numerous questions. [Music]" "[Music] {How fast will the sand spread?} {Will it attract more fish and birds?} {Will the changed currents affect swimmer safety?}" "{How will the visitors use the new landscape?} Right after its completion the sand motor was still a largely empty penninsula of sand. Ready for nature to spread its sand to the beaches" To carefully monitor this process a large team of scientists from knowledge institutes, universities, the government and engineering firms joined forces. They monitored the development of the beach and the seabed, the currents, the dunes, groundwater levels, flora and fauna. As well as swimmers safety, the administrative implications and the value for leisure activities. [Music] Five years after construction, the time has come for first conclusions. There are some exciting results that contribute to the knowledge about coastal management. So far, the sandmotor has done its job when it comes to spreading sand along the coast. Calculations show that the sandmotor could work much longer than the 20 years that were originally expected. The wind and currents spread the sand mainly in a northeasterly direction onto the beach and into the dunes. A lagoon formed along the beach and sometimes cliffs appeared at the north side. Overtime, the lagoon became longer and shallower. In 2016, a new channel was formed as a result of a passing storm. "[Music] {Dune development} Data show that the dune growth in the first five years went slower than expected. This is mainly because the sand has to travel a long way to the dunes." On its path the sand first comesacross the lagoon and the dune lake. Once these are fille dup more, sand will be liekly to find its way to the dunes faster. Fortunately, dunes developed well on the previously built coastal reinforcements "Characteristic types of beach grass have settled on the sandmotoer. Also, sea holly found its home, a protected plant species. [Music]" "At this time its not yet possible to give an answer to whether the sandmotor is better for sea bed life than traditional coastal nourishments. Therefore, a longer period of research is needed. [Music]" "So far the researchers encountered small animals such as the Baltic clam and the sand to worm in the lagoon. These species are not often found in the Norther and South Holland coast. [Music]" The new coastline creates new kinds of currents, therefore swimmer safety is carefully monitored. Rescue services are very satisfied with a newly developed app which could also be tailored for other beaches in the world. Leisure activities on and along the beaches near the sandmotor have increased. Research shows that visitors appreciate this new landscape because of its space and quietness. Five years, in this time we have learned a lot about building with nature. But we still have many years to go. Years in which we expect to gain more knowledge about this ambitious project. Knowledge that contributes to the imporvement of the future coastal management plans and alternative beach nourishment. [Music] Research shows that the sandmotor concept is applicable in several places along the Dutch coast as well as in the rest of the world. One of the first concrete follow-ups are the plans for a sandmotor in Norfold, northeast of London. All the efforts in creating and researching the sandmotor have proven very rewarding so far. {With special thanks to Shore Monitoring 2016 A production of Van Viler Media}

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Dynamic Adaptive Policies

Researcher in Deltares

The speed and the magnitude of sea level rise and socio-economic developments are uncertain. Most adaptation measures require large investments, which are not always feasible. This calls for an approach to support decision-making under uncertainty that produces a dynamic, flexible plan that can be adapted as conditions change and funds become available. This approach is called Dynamic Adaptive Policy Pathways.

Dynamic Policy Pathways

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Coastal Archetypes and Adaptation Pathways

Researcher in Deltares

Generic adaptation pathways for the 6 coastal archetypes; These generic maps will serve as inspiration to develop tailor-made adaptation pathways for any specific coastal area pertaining to the archetype(s); Linked to local policy objectives, adaptation measures and their tipping points. Pathway Generator: to explore policy pathways in an interactive way.

Adaptation is possible, effective and economically robust. In many cases, hard protection may not be practical or desirable (e.g. disruption of sediment supply, viability, access) and innovative adaptation options need to be implemented. Costs (for EU28) can reach up to or even exceed 1.5% of the annual GDP for some nations, but are considerably more affordable for others.

Avoided damage: By 2050, for RCP4.5 and RCP8.5 less than 0.1% of GDP; for the high-end 0.5% of GDP by 2050 and up to 14% by 2100. No severe financial or technological limits to reduce flood risk in the 21st century. Coastal flood risk can be maintained at or below today's levels, provided that large upfront investments can be mobilised where needed. On the financial side, adaptation often requires large upfront investments which are difficult to mobilize, even if the investment is cost efficient on the long run. From an institutional point of view, there is lack of appropriate mechanisms to deal with different stakes at hand.

Adaptation Pathway Generator

Costs and benefits of pathways

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Pathways Generator