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.
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.
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.
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.
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.
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.
Lowland rivers and estuaries are naturally often flanked by vast areas of floodplain that was periodically flooded. The extent of inundation varied between years and formed an integrated system together with the river for moving water from the continental interiors to the ocean. With settlements and farming activities in these floodplain areas, these areas were disconnected to the river system.
With the idea of flood bypasses, these portions of the historic floodplain are reconnected to the river and become inundated during major flood events. They act as relief valves in two ways: conveyance and storage. If this attempt is used in area were these bypasses are not based on historic floodplains, the term relief channels is used.
Culverts typically carry flow in a natural stream or urban drainage channel under a road or railway. In some urban areas, the practice of culverting long lengths of a natural watercourse to gain space for urban development has traditionally been widespread. The practice is now generally recognized as having a negative impact on amenity and biodiversity. By reopening the culverts, these negative impacts can be reduced. In this way, the re-opened culverts can help manage stormwater and slowing down the flow of stormwater.
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.
If fluvial systems don't have sufficient room for natural detention of floodwater in the floodplain, the development and management of flood storage within and adjacent to the natural floodplain is recommended and described in more detail in this measure. It addresses aspects like the process of selecting where to locate the flood storage, deciding how much storage is needed, how to measure the storage capacity, selecting appropriate flow control structures, analysing how the works will perform and making sure that the flood storage scheme is safe in extreme floods.
Urban drainage systems need to be able to deal with both wastewater and stormwater whilst minimizing problems to human life and the environment, including flooding. Urbanization has a significant effect on the impact of drainage flows on the environment: for example, where rain falls on impermeable artificial surfaces and is drained by a system of pipes, it passes much more rapidly to the receiving water body than it would have done when the catchment was in a natural state. This causes a more rapid build-up of flows and higher peaks, increasing the risk of flooding (and pollution) in the receiving water. Many urban drainage systems simply move a local flooding problem to another location and may increase the problem. In many developed counties there is a move away from piped systems, towards more natural systems for draining stormwater.
'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.
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.
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.