Coastal floods or storm surges

Groynes are cross-shore structures designed to reduce longshore transport on open beaches or to deflect nearshore currents within an estuary. On an open beach they are normally built as a series to influence a long section of shoreline that has been nourished or is managed by recycling. In an estuary they may be single structures.

A breakwater is a coastal structure (usually a rock and rubble mound structure) projecting into the sea that shelters vessels from waves and currents, prevents siltation of a navigation channel, protects a shore area or prevents thermal mixing (e.g. cooling water intakes). A breakwater typically comprises various stone layers and is typically armoured with large armour stone or concrete armour units (an exception are e.g. vertical (caisson) breakwaters). A breakwater can be built at the shoreline or offshore (detached or reef breakwater). This measure is not directly addressed to protect the coast in flood events, but can indirectly stabilize the coast by preventing erosion.

The main objective of land claim is neither erosion nor storm reduction.  The aim of land claim is to create new land from areas that were previously below high tide.  These measures can be taken to reduce the exposure of these areas to coastal flooding.  For example, in Singapore and Hong Kong, there are enforced minimum reclamation levels to account for future sea level rise

Venice, Italy, is a city famous around the world for not only its stunning canals and historic buildings, but also for its high vulnerability to flooding. The MOSE system of mobile flood barriers is a bold initiative intended reduce risk, preserve the cherished cityscape, and protect the entire Venice Lagoon from flooding.

The county of Sogn og Fjordane frequently experiences avalanches and landslides, storm surges and flooding. A demonstration project explored the potential for an effective, reliable and cost-efficient early warning system that has a multi-hazard approach and makes use of location and population-based communication technologies, such as mobile phones, as well as social media such as Facebook and Twitter. The system was tested with a sample warning followed by a survey and data analysis to judge its efficacy.

In 2015, the Marin County Community Development Agency (CDA) published a Vulnerability Assessment based on information from technical advisors, utility managers, and West Marin residents. The Assessment summarizes the expected timing and extent of impacts, laying a foundation of knowledge to guide adaptation planning.

Skara Brae is one of Scotland’s most significant and famous UNESCO World Heritage Sites and it has been under constant threat of damage due to coastal erosion for decades. Fortunately, a seawall protects the base of this archaeological site from the erosive power of waves and storm events.

In 2014, the London Resilience Partnership developed the second Mass Evacuation Framework for the city of London. The purpose of this Framework is to offer guidance to responders managing a mass evacuation of displaced persons and, where appropriate, other living creatures.

The Framework has been developed by the Multi-Agency London Resilience Partnership Mass Evacuation Group. This group consists for example of the City of London Police, London Fire Brigade Emergency Planning, Environment Agency, Ministry of Defence (London), or Network Rail.

Cascais is a Portuguese city on the Atlantic coast and 30 km west of Lisbon. Within the project BASE, researcher supported the participatory ICZM approach to develop a Climate Adaptation Action Plan.

On the island of Kauai, Hawaii in the USA, the local governing county has implemented flexible and protective coastal setbacks that protect communities from coastal erosion and avoid shoreline armouring in the long term.

Criel sur Mer is a small town in Normandy in the region of Northern France, known for its stunning coastline of steep chalk cliffs. Erosion of the cliffs in Criel sur Mer is occurring rapidly as a result of climate change but also due to man-made construction works further up the coast. In Criel sur Mer a short piece of land on the coast that is eroding rapidly and several homes built near the sea are threatened by the predicted collapse of the cliff. In particular, a street of homes were faced with immediate danger from erosion. Between 1995 and 2003, the local administration organized the abandonment and demolishment of 14 homes due to imminent risk from natural disaster under the Barnier Law. The adoptive policy was to do nothing against cliff erosion and to demolish and relocate those in immediate threat and compensate them fairly for their lost property.

In 1996 the Dutch Department of Transport, Public Works and Water developed a program called ‘Roads to the Future,’ and a component of this project was the testing of a pilot floating road. The testing of the pilot took place in 2003 and aimed to create a 70 meter stretch of road in the town of Hedel, the Netherlands to mitigate against rising ground water levels. The floating road was designed to maintain access and flexibility in traffic and movement and prevent the isolation of a village otherwise cut off by flooding.

Located on England’s North Norfolk coast, the Titchwell Marsh is a key piece of the North Norfolk Coast Special Protection Area (SPA) and Special Area of Conservation (SAC). This coastal wetland ecosystem includes freshwater and brackish habitats and is currently protected from the erosive power of waves by seawalls which are becoming increasingly weakened.

The Titchwell Marsh Coastal Change Project aims to protect vital freshwater habitats from both coastal erosion and sea level rise through managed realignment and seawall reinforcement, and mitigate and compensate for the loss of important brackish habitats.

Not only land or buildings can be elevated. In Marinas also watercrafts can be allowed to adjust to fluctuations of water level. This concept shows a simple idea of how a 'flood proof mooring' system could look in a Marina in the RISC-KIT case study area in Kiel.

A construction of an elevated wooden pathway alongshore and cross-shore of about 1500 m, and the construction of a dune fences were implemented in the coastal town of Praia de Faro (Portugal). The fences helped to trap sand in the dune areas leading to a growth of the dune system. The wooden path played also an important role in the dune recovery.

Amager Beach is a constructed island in the southern part of Copenhagen. It was built between 2004 and 2005. It not only serves recreational purposes for the local population, but is also a coastal defense structure to protect the main coastline. This artificial approach is a very good example of combining ecosystem based approaches with coastal defense aspects.

In 2008 the Marina Gangplank Wharf, located in Washington D.C., USA, published a revised version of a ‘Severe Weather Preparedness Plan’. This plan is designed to provide slipholders and marina employee’s guidance with respect to the actions the marina will take at the approach of severe weather and/or hurricane landfall in the Washington Metropolitan Area.

Emergency plans for Marinas can help to be better prepared for storm floods. In preparing an emergency plan, certain information has to be provided.

Coral and oyster reefs are considered to be types of coastal wetlands. As a natural coastal defense they are a buffer for coastlines against waves. Reefs are threatened by rapid environmental change, making it very important to protect and restore reefs.

Coastal and marine environments are usually characterized by beautiful landscapes and rich ecosystems of great importance, offering elements such as rich biodiversity. They also attract human activities such as tourism and industrial uses. However, the co-existence of human activities and natural resources often creates conflicts of use in the coastal zone.

Management policies are an important means of implementing planning in order to minimise, prevent or resolve use conflicts. The development of a coastal and marine spatial planning system presents an opportunity for the implementation of an overall strategy of conservation, sustainability and management to maximise future economic profit.

This case study is about enhancing the natural dynamics of the dunes and the sand transport on the Wadden Sea island of Terschelling, Netherland 

Flood forecasting is an essential tool for providing people still exposed to risk with advance notice of flooding, in an effort to save life and property.

To minimize the loss of lives and reduce other flood impacts, an area should be evacuated when the depth of standing water due to flooding is already or is expected to become high. Such floods are defined as those which are expected to cause buildings, including residential houses, to be washed away or seriously damaged by the flooding.

The purpose of early warning systems (EWS) is simple. They exist to give advance notice of an impending flood, allowing emergency plans to be put into action. EWS, when used appropriately, can save lives and reduce other adverse impacts.

It is vital to recognize that even after the implementation of non-structural flood mitigation measures residual flood risk will remain. It is of paramount importance to make plans to deal with flood events and their aftermath. This involves multiple activities which can be included as part of a flood emergency plan. In this section there is an overview of the elements central to emergency planning.

An urban flood event requires immediate measures to ensure that citizens have safe drinking water, including appropriate excreta disposal, disease vector control and waste management. However, during and after a flood event is not necessarily the best time to communicate health messages to individuals and organizations, as they may be dispersed and not have access to the necessary resources. Health Awareness Campaigns are vital ‘soft’ interventions alongside hardware provision (waste water treatment, for example); together they can help preserve public health by increasing preparedness. Health awareness and hygiene promotion campaigns must not be carried out independently from water supply and sanitation, and vice versa.

Flood risk awareness is the cornerstone of non-structural flood risk management. All actions to minimize the impact of flooding hinge upon stakeholders becoming aware these are both necessary and desirable. Ignorance of flood risk encourages occupation of the floodplain, in the first instance, and can allow appropriate building design practices to fall into disuse. In the event of a flood, the lack of awareness of risk can result in a failure to heed warnings to evacuate, thereby endangering lives.

Cliff stabilization is a coastal management erosion control technique. Generally speaking, the cliffs are stabilised through anchoring (the use of terracing, planting, wiring or concrete supports to hold cliffs in place), smothing the slope, or dewatering (drainage of excess rainwater to reduce water-logging).

Managed realignment is a measure that usually results in the creation of a salt marsh by removing costal protection an allowing for an area previously protected from flooding to become flooded. Managed realignment is a measure dealing with sea level rise and coastal erosion. It is also often a method that replaces hard coastal defense measures with soft coastal landforms. Rather than relying on hard structures for defense, managed realignment depends on natural defenses to absorb or dissipate the force of waves.

Saltmarsh and mudflats are usually located together with mudflats in front of the saltmarsh. Saltmarsh vegetation and saltmarsh creeks help manage floods by dissipating wave and tidal energy.  They are valuable barriers to the risks of flood, as they dissapte wave and tidal energy. Saltmarshes used in combination with other measures can have beneficial outcomes to managing climate change impacts. Even a small width of fronting saltmarsh can significantly reduce the height of sea walls required to achieve the same level of protection and thus also reduce initial construction costs. Having saltmarsh fronting will also significantly reduce maintenance costs due to the reduced exposure to wave and tidal energy.

Wetland restoration can serve to reduce coastal flooding and erosion. It has also additional benefits like provide new habitats or improve the landscape for recreational purposes. Wetland restoration relates to the rehabilitation of previously existing wetland functions from a more impaired to a less impaired or unimpaired state of overall function.

To reduce cliff erosion and its consequences – landslide, collapse, falling of rocks – cliff strengthening techniques aim at increasing the strength and overall stability of the slope by minimizing landside pressures.

A breakwater is a coastal structure (usually a rock and rubble mound structure) projecting into the sea that shelters vessels from waves and currents, prevents siltation of a navigation channel, protects a shore area or prevents thermal mixing (e.g. cooling water intakes). A breakwater typically comprises various stone layers and is typically armoured with large armour stone or concrete armour units (an exception are e.g. vertical (caisson) breakwaters). A breakwater can be built at the shoreline or offshore (detached or reef breakwater). This measure is not directly addressed to protect the coast in flood events, but can indirectly stabilize the coast by preventing erosion.

Beach drains comprise perforated land drain pipes buried below the upper beach surface, and connected to a pump and discharge. The concept is based on the principle that sand will tend to accrete if the beach surface is permeable due to an artificially lowered water table. The system is largely buried and therefore has no visual impact.

A sea dike is a manmade structure designed to protect low-lying areas from flooding from the sea or ocean. They typically are designed with several components including a sand core, a watertight outer protective layer, toe protection and a drainage channel. Sea dikes are intended to withstand and resist water and wave action. They are widely used in countries with low lying geographies such as Vietnam, Bangladesh, Thailand, the Netherlands and parts of the United States.

Surge barriers and closure dams are protective measures designed to prevent a storm or high tide from flooding an area. A surge barrier is often a movable structure that is signaled to close prior to a storm and reopen to facilitate transport of goods and boats or if protecting an estuary, to allow natural movement of tides. A closure dam on the other hand is a permanent structure. Both are significant physical barriers that require advanced civil engineering and substantial construction. They provide a physical barrier and are used to protect coastal communities, tidal inlets, rivers and estuaries from extreme weather events.

Dikes and dams need regular maintenance and strengthening to keep their protection capacities and meet safety requirements. In addition, climate scenarios for sea level rise and extreme weather conditions can lead to reconsidering safety requirements and building new protections on identified weak points or heightening and strengthening existing ones. The design of existing dikes and dams can be modified to fulfill different purposes.

A temporary flood barrier is one that is only installed when the need arises (that is, when high flood levels are forecast). A demountable flood defence is a particular form of temporary defence that requires built-in parts and therefore can only be deployed in one specific location. The removable stoplog defence is a particular form of demountable defence applicable only for small openings in a permanent defence. The more commonly adopted gate option for closing off a gap in a floodwall is neither temporary nor demountable, as it is part of the permanent defence and is left in place all the time (albeit normally in an open position).

A seawall or a revetment is a structure made of concrete, masonry or sheet piles, built parallel to the shore at the transition between the beach and the mainland or dune, to protect the inland area against wave action and prevent coastal erosion. Seawalls are usually massive structures designed to resist storm surges.

'Elevation of buildings' and ' Land raising' are two separated measures with the aim to elevate exposed elements.

Moving a building out of the existing flood hazard area is the safest solution among several retrofit-ting methods; however it is also usually the most expensive method (FEMA, 2009). When a community acquires a flood-prone home from the owner, relocation is often applied, as well as demolition of the building. The relocation is not only limited to buildings, it can also be applied to other exposed coastal infrastructure.

Dryproofing makes a building watertight and substantially impermeable to floodwaters (FEMA, 1993). Compared to wetproofing, dryproofing requires a more reinforced building structure to withstand floodwater pressures and impact forces caused by debris. Other important factors to be considered in dryproofing are watertight closures for doors and windows, prevention of floodwater seepage through walls, and check valves to prevent reverse flows from sewage.

Coastal setbacks are an demarcated area where all or certain types of development are prohibited. Coastal setbacks can be measured either as a minimum distance from the shoreline for new buildings or infrastructure facilities, or may state a minimum elevation above sea level for development.  Setbacks determined by distance from the shore are used to combat coastal erosion, while setbacks determined by evaluation are used to control flooding.

Wetproofing (or wet floodproofing) is different from dryproofing in that it allows flood water to enter a structure, though both floodproofing methods have the same purpose, that of preventing damage to the structure and its contents and creating no additional threats to public safety (FEMA, 1993).

Sand dunes are wind forms elements on sandy coasts and represent a natural coastal protection measure. Natural processes like erosion and human interference (like coastal protection measures, changing coastal processes, tourism) can have a negative impact on dunes. Rehabilitation with feeding sand or planting vegetation can reinforce the dunes.

Highly dynamic coastal systems (like sandy beaches, dunes or estuaries) might be best managed by not interfering with the natural processes, but instead accepting that change will occur and adapting backshore management accordingly. Key in this approach is a proper monitoring of the processes to analyze and evaluate the changes (for examples at eroding cliffs or dunes). With a proper planning horizon, these changes can be anticipated and with enough room for the environment to involve this can be a very cost-extensive approach.

Artificial reefs are shore parallel rock mound structures set part way down the beach face. They may be long single structures or form a series of reefs extending for some distance alongshore. They are submerged for at least part of the tidal cycle, and are therefore less intrusive on the coastal landscape, have less impact on upper beach longshore processes and add a new intertidal habitat to sandy foreshores.

Groynes are cross-shore structures designed to reduce longshore transport on open beaches or to deflect nearshore currents within an estuary. On an open beach they are normally built as a series to influence a long section of shoreline that has been nourished or is managed by recycling. In an estuary they may be single structures.

The municipality of Timmendorfer Strand developed and implemented a coastal protection strategy using a participatory process. This process was a key element for the successful implementation of the measure. Although this measure was very expensive, a cost-benefit analysis shows that the benefits are higher than costs.