Prevention

Flood hazard mapping is an exercise to define those coastal areas which are at risk of flooding under extreme conditions.  As such, its primary objective is to reduce the impact of coastal flooding.  However, mapping of erosion risk areas may serve to achieve erosion risk reduction.  It acts as an information system to enhance our understanding and awareness of coastal risk.

Attica, Greece is a region with extensive wetlands that include streams, estuaries and coastal marshes. The land area is also heavily in use for agriculture and experiences competition from various anthropocentric uses which have created a largely degraded environment. The wetlands that dot the region, are largely considered by communities as the remaining environmental hotspots and serve not only as ecologically important areas but peoples’ remaining contact with nature. They are for this reason, closely tied to community use and general well being. To protect these wetlands, an Attica Wetland Action Plan was developed.

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.

Near to the RISC-KIT Case Study in Emilia – Romagna, a LIFE+ “LIFE RINASCE” project has been implemented in 2014 to improve some of Emilia - Romagna drainage channels in the Po floodplain. Project leader is the Emilia Centrale Land Reclamation Consortium, in collaboration with the Emilia -Romagna Region. The project was started in 2014 and will run the end of 2018 with a total budget of almost 2.1 million €.

By 2002, historic Clavell Tower was deemed to be at serious risk of collapsing under the crumbling Dorset coastline at its base. The most technically, socially, and financially feasible solution was to simply dismantle the empty tower and reconstruct it further away from the cliff’s edge on more stable footing. This resulted in a reinvigorated heritage site saved from the dangers of coastal erosion.

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.

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.

The Clacton to Holland-on-Sea (UK) stretch of coastline has suffered from significant sediment loss, which negatively impacts the local community and economy. Collectively, five kilometres of beach are at risk of washing away including nearby tourism promenades and over 3000 homes and businesses. In response, a major sea defence project is underway to fortify the coast through construction of new rock groynes and beach nourishment activities. It is expected that this project will reduce coastal erosion for the next 100 years.

The Ventura County Chapter of the Surfrider Foundation in California, USA decided against traditional coastal defence measures to reduce beach erosion at a popular beach spot called Surfer’s Point. Along with other stakeholders, the County instead designed a two-phase plan to strategically relocate a parking lot, pedestrian path, and bike path away from erosion zones.

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.

In the face of increasing beach and dune erosion, the community of Quend-Plage, located on the Picardy coast of northern France, installed a beach drainage system in 2008. As a result of this, the macrotidal beach of Quend-Plage has been stabilized, preserving both natural habitats and recreational spaces.

The beach of Pevensey Bay (UK) is a shingle barrier beach under threat from flooding and coastal erosion. Today, the beach is managed in an adaptive manner developed by Pevensey Coastal Defence, where management activities respond to changes in risk and beach recharge and beach recycling is undertaken.

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 vulnerability assessment can be used as an informal spatial planning instrument to identify, quantify, and prioritize vulnerabilities in a system. In coastal areas effects of climate change can add additional pressure on these systems. A vulnerability assessment addresses these pressures and analyzes the risks and adaptation capacities to cope with these risks. Results are an important tool in regional and local spatial planning.

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.

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.

The case study shows how sand replenishment at the west coast of Denmark has become the main measure to face coastal erosion. Experiences in the last years showed, that replenishments at the foreshore seem to be the most effective and ecosystem friendly version of beach nourishments.

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

When rivers are denied the space to meander due to levees, rock revetments, or other impediments, many beneficial river services are diminished. Setback levees increase channel capacity for carrying floodwaters. Once a levee is setback, the river may begin to meander and this poses a challenge to implementing riparian restoration on the floodplain.

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).

Shingle beaches are mobile structures developed in high-energy environments that are very efficient at absorbing and dissipating wave energy. Restoration of shingle beaches on the foreshore can create a more desirable morphological profile that is better able to dissipate wave energy and attenuate storm surge.

In the RISC-KIT Case Study area of Emilia-Romagna (Italy), a study has been undertaken to gain insights about improvements of the design of beach scraping operations. Here, a numerical modeling approach was used to find more appropriate beach scraping design.

Communication to and participation of the public is an important aspect of many planning processes, this also includes the development of DRR plans and strategic alternatives. This description is based on a project handbook that has been especially designed to support regional and local administrations in the planning and implementation of communication and public participation processes in flood prone areas. The findings of this report can also be applied to coastal areas.

The Multi-Criteria Analysis (MCA) is one of the five tools used to assess the proposed measures in each of the RISC-KIT case studies with respect to criteria that capture the key dimensions of the decision-making process. The purpose of the MCA is to bridge the disciplinary divide between engineering sciences and social sciences, facilitate the communication and dissemination of project results to a broad audience, and to integrate scientific knowledge with local knowledge with the purpose of improving the assessment of coastal risks.

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.

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).

The construction of floodwalls and embankments has been the traditional means of protecting lowlying communities and infrastructure against flooding. Although the primary function of a wall or embankment may be flood defence, such structures also frequently have a secondary function – quite often with the aim of enhancing the environment or improving the amenity or both.

Dredging is the general term used for the excavation of material below water level either as a maintenance activity or as part of channel enlargement works. The main purpose of dredging is either to maintain the navigation depth or the flood capacity, or sometimes both.

Bank protection is needed where there is the risk of erosion of the bank and where this erosion would cause economic or environmental loss. If there is sufficient space available, it may be possible to reduce the need for bank protection by re-profiling the bank to a flatter slope to reduce velocities and encourage good vegetation growth. Even if bank protection is still required, it may be less severe if a flatter slope can be achieved, or may only be required below normal water level.

Traditionally, interventions in river channels have been carried out to reduce flood risk at a particular location. This approach has produced artificial river geometries which have often been found, for a variety of reasons, to be unsustainable. A core principle of modern river engineering is that, in general terms, rivers tend to return to their natural ‘regime’ state, in which the main channel has the capacity for a particular flow and no more.

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.

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.

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.

Cost-Effectiveness Analysis (CEA) is a methodology used to compare different approaches to achieve pre-defined adaptation targets. CEA can be used to analyse both technical or project oriented work and policy or programme approaches, providing comparisons and rankings of options with the same adaptation objective, or identifying the least cost combination of options.

For the rehabilitation of a dune system, an elevated wooden pathway over the shore and the dunes and a dune fence were created. They were created to restore the physical and ecologic characteristics of the dunes at a natural Park at Praia de Faro (Portugal). The cost effectiveness is analyzed in this description and compared to beach nourishment.

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.

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 new form of beach nourishment is the 'Zandmotor' (sand-motor) undertaken in the Netherlands. Instead of having smaller nourishments in a time period of 4 to 5 years, the water authority Rijkswaterstaat formed 21.5 million m3 of sand into a peninsula near Ter Heijde in 2011. In the beginning, the peninsula stretched 1 km into the sea and was about 2km wide. The idea is that waves, current and wind spread the sand along the coast and thus enhance the coastal protection and at the same time create a dynamic natural and recreational area. It was expected to have a repeating interval of only 15-30 years.

Beach nourishment describes a measure where sediment that is lost due to longshore drift or erosion on a beach is replaced from material outside of the eroding beach. This results in a wider beach that can reduce storm damages and coastal erosion. Beach nourishment is typically a repetitive measure, since it does not remove the physical forces causing erosion, but is a measure that mitigates the effects of erosion.

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. 

Beach scraping is recovering material from the berm at the foreshore and placing it on the backshore at the foot of the dunes or the cliff.