Channel, Coastal and Floodplain Works

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.

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 €.

As in many other cities, the former dominating strategy for Oslo’s rivers and streams was to enclose them for practical reasons. This approach has changed and the City is actively reopening waterways to make them accessible for people, facilitate increased habitat for biodiversity and handle storm water more efficiently.

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 aim of the Wallasea Island Wild Coast project is to recreate a natural intertidal coastal marshland to combat the threat of climate-induced coastal flooding. The recreated mudflats, salt and brackish marshes, saline lagoons, and pastures will provide a range of habitats for coastal birds and other wildlife on the Essex coast.

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.

Construction of the first components of the Wroclaw floodway system in Poland, one of the largest flood protection systems in Europe started in 2011. The project includes large scale improvements to the system of river channels and flood defenses which provide protection from the floodwaters of the River Odra that flows through Wroclaw. The goal of the project is to reduce the city’s flood risk to a probability of less than a 1000-year event.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.