Putting sustainability at the heart of land reclamation

While land reclamation projects can be carefully engineered to minimise impacts on marine ecosystems, there are ways to build with nature to create a positive impact on, for example, aquatic life. 

When reclamation projects are planned in areas of already deteriorating biodiversity, the introduction of reclamations can be used as a catalyst for developments to protect the remaining habitats or relocate parts of them offsite. This way, the reclamation efforts can have a positive impact on the system. 

Examples of low-biodiversity habitats where land reclamations are being developed include Jakarta Bay and Manila Bay. The following two examples illustrate how adapting shoreface structures aid in accommodating marine life.

In our recent work for reclamation projects in Cordova (Philippines), Haskoning conducted extensive assessments of how proposed solutions would impact local waters and marine life. The marine ecosystem is very important to the local population, because their livelihoods depend on the fish the ecosystem produces. 

To promote greater biodiversity, we incorporated extended berms and tidal pools into the reclamation edges. This creates rock pool habitats when the tide recedes, which encourage a wide variety of species. 

We collaborated with master planners to adjust the footprint and shape of the reclamations to maintain green/blue corridors for marine life. And we developed edge designs with long, shallow slopes, suitable for planting of mangroves or coastal forests. This way, the communities surrounding the area can benefit from ecosystem improvements.

In the Netherlands, Haskoning worked on the development of IJburg, an urban development district in the eastern part of Amsterdam, bordering the Vecht river. For further expansion, reclaiming islands was found the most suitable solution, after careful environmental considerations. 

The new islands would cover local mussel beds, affecting local waterfowl that feed on them. To offset this, new improved mussel beds were created as part of the project. Monitoring has shown that concentration of mussels on the new beds exceeds the original beds. 

In addition, the creation of shorelines and sheltered areas will create more feeding grounds for waterfowl and improve the water quality, as it allows sludge to settle.

Like any coastline, reclaimed land is susceptible to erosion and flooding – and the risk of this is growing as climate change accelerates. However, consultants have a toolkit ranging from grey to green solutions to mitigate coastal flood risks and floods from rainwater on reclaimed land.

For example, grey solutions such as seawalls and dikes, made from concrete and rock, will protect areas against coastal flooding. They can be very safe and sound, but lack adaptive capacity to future changes. On already eroding coastlines, they may generate more erosion or cause knock on impacts for areas elsewhere. 

Green-grey solutions, where natural elements are combined with grey structures, or full NbS such as mangrove forests could be a better alternative. They can dampen waves, catch sediment, and allow an area to grow and adapt to sea-level rise. However, creating those environments in deep water may be tricky and require careful planning and preparation. 

Reuse of dredged materials may play a role in this, as they can reduce offshore disposal. Reused material can also aid in increasing foreshores which can subsequently be colonised by species such as mangroves. 

And what about flooding from rivers and rainwater? Land reclamation locations are often carefully selected to avoid obstructing river flow, omitting the risk of fluvial flooding altogether. Other measures to reduce fluvial flooding are discussed in this blog. 

Rainwater (or pluvial flooding) is a serious threat, but there are opportunities to designate catchment areas on reclaimed land like natural rain gardens where permeable surfaces promote higher levels of infiltration. This reduces flood risks while filtering pollutants from rainwater. And collected water can also be reused for other purposes, such as flushing toilets or as cooling water.

A common concern around reclaimed land is that it will impact local water quality. Every land reclamation project we undertake includes water quality studies to avoid these risks. Final designs consider water quality modelling to confirm adequate water circulation, and flushing measures are introduced where required. During construction, state of the art placement techniques are employed to reduce disturbance of sea beds and spread of fill material to reduce plumes; in extreme cases silt or turbidity curtains may be used to confine the spread of fine sediment during sand filling or dredging activities. This ensures sediment plumes are reduced, protecting aquatic habitats and complying with environmental regulations. 

Looking at more permanent solutions, there are other ways NbS can be incorporated into land reclamation to maintain – or even improve – water quality. For example, rehabilitating mangroves will improve water quality as mangrove roots hold onto sediment, reducing erosion with their root systems and capturing sediment from turbid water. Mangroves also absorb nutrients and filter pollutants from runoff that can otherwise lead to water impurities. Implementation of mangroves along the coastline has been part of our work in the north of Manila Bay. 

In general, there are two ways NbS can help maintaining or improving water quality. The first involves the ecosystems themselves, such as shellfish or mangroves that are capable of filtering water. For example, 300 mussels can filter about one cubic metre of water per day, removing harmful algae, bacteria, and even metals. These natural water filters remove pollutants like nitrogen, resulting in clearer and cleaner water. 

The second method involves creating areas sheltered from waves and current, where turbid water can calm down. This allows for fine particles to settle and be removed from the water column, increasing water quality. These kinds of measures go a long way to restoring and maintaining the biodiversity of the original coastline.