Water-Gate is a flexible emergency flood dam that harnesses the power of floodwater to automatically fill, unfold and stabilise itself.
Water-Gate is also the latest generation of cofferdam; it simplifies river works, quickly and effectively combats pollution, and makes better use of natural water points for firefighting.
Water-Gate can be installed on any kind of terrain. It is inexpensive and protects the environment.
Storm surge gates and flood barriers are fixed installations that allow water to pass in normal conditions and have gates or bulkheads that can be closed against storm surges or high tide to prevent flooding. They can close the sea mouth of a river, the sea mouth of a waterway or a tidal inlet. These barriers are major infrastructure systems. Their implementation can be complemented with other grey and green storm surge and flood protection measures, such as dikes, seawalls and beach nourishment.
The implementation of an advanced flood forecast system and of an early warning system is required to ensure the prompt activation of storm surge gates and flood barriers before the storm surge or the flooding event actually occur. In normal conditions, storm surge gates and flood barriers allow the free passage of water, enabling regular navigation and natural water exchange in tidal inlets.
Storm surge gates and flood barriers are built to protect highly vulnerable urban areas and infrastructure where storm surges and sea flooding could have major impacts. Due to their poor flexibility and the high direct and indirect associated costs, storm surge gates and flood barriers must be accurately designed. This design should take into account projected changes in sea level and in storminess due to climate change, since the beginning of the planning stage. A long-term adaptive management plan of the structure and of other complementary strategies against flooding in the face of climate change can favour the success of the measure, avoid possible failures, and minimise environmental impacts. Due to their high costs and potential impacts, storm surge gates and flood barriers are relatively rare. They are used to protect particularly vulnerable and precious areas. Most known examples in Europe include:
The
Thames Barrier
(operative since 1983), London, can close off the Thames River just east of the City of London, at a point where the river is about 520 metres wide.
The
six storm surge barriers operated in the Netherlands
by the Ministry of Infrastructures and Public Works (Rijkswaterstaat) to protect the most vulnerable parts of the country from flooding. The largest barriers (the Eastern Scheldt Barrier and the Maeslant Barrier are part of the Delta Works and are located at the southern North Sea coast. If the water level rises to a dangerous level, the barriers close. The water is then prevented from flowing inland via rivers or estuaries.
The Venice barriers (also called the
‘Mose’ system
) are built across the three outlets of the Lagoon of Venice to the Adriatic Sea. The system is composed of four barriers with 78 flap-gates covering a total length of 1.6 km. It became operational, though in a test phase, since autumn 2020.
The
St. Petersburg barrier
(completed in 2011, Neva Bay - eastern part of the Gulf of Finland) is part of a large flood prevention facility complex to protect the city from flooding, with an overall length of 24.5 km.
IPCC categories
Structural and physical: Engineering and built environment options
Stakeholder participation
Due to the complexity of the engineering solutions, the significant costs of construction and maintenance, and the possible expected environmental impacts, proposals for storm surge barriers require wide and prolonged stakeholder and public participation. Moreover, these structures generally require an Environmental Impact Assessment procedure that, according to the EU EIA Directive, must ensure the right to access information and to participate in the environmental decision making. Similarly, the EU Floods Directive, and the EU Water Framework Directive establish public participation processes that may refer to these projects as well.
The construction phase requires considerable consultancy with engineers, local communities, NGOs, local authorities and representatives of policy sectors that can be affected by the measure (e.g. fisheries, maritime transport, tourism, etc.). A strong political support and wide public consensus, together with a long-term vision, is needed to ensure success in the implementation of such complex measures.
Success and Limiting Factors
Storm surge gates and flood barriers provide a high degree of protection of low lying coastal areas by providing a physical barrier against flooding. In particular, they are used to protect highly vulnerable and precious coastal urban and infrastructure areas. Existing gates and barriers (Netherlands, UK, Venice, St. Petersburg) have provided effectiveness against storm surges. The use of mobile barriers, instead of fixed structures, allows waterways to remain open during normal conditions. They allow to limit the (environmental, social, economic) impacts related to a permanent closure. Success examples of mobile barriers in the world are shared through I-Storms, the international network for storm surge barriers. It aims at facilitating knowledge exchange and collaboration of experiences of barrier planners and operators facing similar challenges.
One key limiting factor of the storm surge gates is the high capital and maintenance costs since significant investment is required to build these structures and to continually maintain them. The environmental impact of such measures is another key issue to be considered. The construction of mobile barriers can cause large modifications of natural environments and related environmental impacts must be properly assessed and minimised in the design phase. If too frequently operated, mobile gates and flood barriers can limit water exchange in estuarine and lagoon habitats.
Another important issue is the extent to which these barriers will remain viable in the face of future climate change and sea-level rise. In the case of London, the Thames Barrier is expected to continue to protect the city to its current standard up until 2070. The Thames Estuary 2100 Plan was designed to be adaptable to different rates of sea level rise and changes affecting the estuary. The plan identifies different options for improving or replacing the Thames Barrier. Full review and update of the Plan is scheduled every 10 years.
Other limiting factors are related to the capacity of the forecasting systems to early predict in a reliable way the flooding event, thus allowing to activate the procedures of gates closing on time. The time needed to close the barriers can vary according to both specific technical aspects and to complex management issues of the whole area. It can imply the interruption of navigation, port services and other activities. Continuous investment in research and technological innovation is essential to improve the reliability and precision of forecasting systems and their use under operational conditions.
Finally, the technical failure of the system (e.g. a barrier not closing properly) can be perceived as a large risk by the public. Acceptance of the work by the public and stakeholders can be fostered by an overall transparency in the decision-making process. , Proper stakeholder engagement, public consultation and informative workshops are proven means for transparent process settings.
Costs and Benefits
Storm surge gates and flood barriers provide a high degree of protection for urban settlements and infrastructure against seaward storm surges and related flooding. Compared to fixed gates, this type of infrastructure provides a more flexible solution. It allows waterways to be open in normal conditions for the natural water exchange and the movement of aquatic species as well as for human activities such as shipping and fisheries.
Large capital and maintenance costs are required to design, build, and maintain storm surge gates and flood barriers. Investment in monitoring hydrological parameters, flood forecasting and warning systems must also be ensured, to improve robustness and precision of information needed for the activation of the system in a prompt manner.
The construction of the Thames Barrier cost GBP 535 million in 1982 (about GBP 1.7 billion or EUR 2.5 billion in 2007), according to the UK Environment Agency. Operational costs are about GBP 8 million a year (about EUR 9.5 million in 2013 prices). Building the Mose system (including four mobile barriers at the Venice lagoon inlets) cost EUR 5.49 billion, according to official estimates. The estimate also includes two additional activities, i.e; the requalification of the facilities of the Venice Arsenal for the maintenance and operation of the MOSE system, and the requalification works needed to improve the integration of the mobile barriers within the lagoon environment.
Legal Aspects
The EU Floods Directive provides a legal framework for flood actions and defence. As major infrastructure systems, storm surge gates and flood barriers are likely to be part of the flood protection plan required by the Directive, which undergoes a strategic environmental assessment (SEA Directive). As coastal works, storm surge gates and flood barriers fall into Annex II of the Environmental Impact Assessment: Member States decide whether projects in Annex II should undergo an EIA procedure, either on a case-by-case basis or in terms of thresholds and criteria.
Implementation Time
The construction of these complex and often largescale engineering solutions is a long process which must be preceded by a detailed modelling, assessment, and design phases. Normally it takes more than 15 years.
Life Time
Storm surge gates and flood barriers have a long life expectancy (more than 50 years). Continuous maintenance is needed to ensure their full life-time and proper functioning without risks. Monitoring of potential effects on the environment is also essential.
UNEP-DHI (2016). Managing climate change hazards in coastal areas. The coastal hazard wheel decision-support system: Catalogue of hazard management options. United Nations Environment Programme & Lars Rosendahl Appelquist ISBN: 978-92-807-3593-2
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