Estuarine floods

Based on kindly provided information by the Scottish Natural Heritage

Hold the line

Grey infrastructure

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.

Groynes reduce longshore transport by trapping beach material and causing the beach orientation to change relative to the dominant wave directions. They mainly influence bedload transport and are most effective on shingle or gravel beaches. Sand is carried in temporary suspension during higher energy wave or current conditions and will therefore tend to be carried over or around any cross-shore structures. Groynes can also be used successfully in estuaries to alter nearshore tidal flow patterns.

Technical feasibility

Groynes can be made from different material. Rock is often favoured as the construction material, but timber or gabions can be used for temporary structures of varying life expectancies (timber: 10-25 years, gabions: 1-5 years). Rock groynes have the advantages of simple construction, long-term durability and ability to absorb some wave energy due to their semi-permeable nature. Wooden groynes are less durable and tend to reflect, rather than absorb energy.

Groynes along a duned beach must have at least a short “T” section of revetment at their landward end to prevent outflanking during storm events. The revetment will be less obtrusive if it is normally buried by the foredunes. Beach recycling or nourishment is normally required to maximise the effectiveness of groynes. On their own, they will cause downdrift erosion as beach material is held within the groyne bays.

Groynes can have a significant impact on the shoreline, and schemes should always be undertaken under the supervision of a competent coastal consultant. As with all rock structures on the shoreline the rock size, face slopes, crest elevation and crest width must be designed with care. Rock size is dependent on incident wave height, period and direction, structure slope, acceptance of risk, cross-sectional design, and the availability/cost of armour rock from quarries. In general 1-3 tonne rock will suffice for the landward parts of the groynes, provided that it is placed as at least a double layer, with a 1:1.5 to 1:2.5 face slope, and there is an acceptance of some risk of failure. Larger rock, probably 3-6 tonne, may be needed for the more exposed body and seaward head of each structure.

The groyne berm should be built to the anticipated crest level of the beach. The groyne berm length should equal the intended crest width of the updrift beach. The groyne should extend down the beach at a level of about 1m above the anticipated updrift shingle beach, normally at a slope of about 1:5 to 1:10. The groyne head should extend down into the sand beach, allowing for some future erosion.

As a general rule, groynes should not be built on an open beach unless construction is accompanied by a commitment to regular recycling or nourishment. Without this commitment the groynes are likely to cause downdrift erosion as the upper beach becomes starved of sediment. Where there is a plentiful sediment supply, or where downdrift erosion is not considered to be a significant issue, then recycling may not be required.

Timber groynes must be built from hardwood to endure the harsh shoreline environment. Much hardwood comes from tropical sources, making it both costly and potentially environmentally unacceptable. Timber groynes tend to reflect, rather than absorb, wave energy making them significantly less effective than rock on exposed coasts. They are also more likely to structural failure due to formation of scour channels around their seaward ends.

Political & social feasibility

Rock structures on recreational beaches should be built with a view to minimising the potential for accidents involving beach users slipping between rocks

Cost of implementation & maintenance

The costs of groynes are considered as moderate

Ecological feasibility

Implementing groynes disrupts natural processes. The effects must be properly monitored and if possible compensated.

Key lessons learnt

Provided that groynes are used in appropriate locations, they reduce dependency on regular recycling or nourishment, and therefore reduce future disturbance of the shoreline environment. Localised accumulations of beach material will encourage new dune growth. Recycling, fencing and transplanting will help to keep the revetment sections buried, thereby enhancing habitat regeneration.

Measure category

Mitigation

Breakwaters

nst — Wed, 22 Mar 2017 08:49:13 +0000

Breakwaters nst Wed, 03/22/2017 - 09:49

Combined approach (grey + green)

Hold the line

Grey infrastructure

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.

Based on the information available on the ClimateAdapt Platform

To build breakwaters, rock size, face slopes, crest elevation and crest width and toe protections and aprons should be designed according to the natural characteristics of the sites as these factors have an important impact on the shoreline. Sand may build up behind breakwaters to form salients. Sand can accumulate enough to connect with the breakwater and form a tombolo (a stretch of sand developed by wave refraction, diffraction and longshore drift forming a ‘neck’ connecting the structure to the shore). Considering the significant impact these structures have on the coastal environment, they should only be considered as part of a global adaptive management policy, taking into account the characteristics of the specific site and the potential effects on the whole coast. The construction of breakwaters could also be linked to a beach nourishment programme, and breakwaters can be used in a protected beach nourishment approach.

Stakeholder participation

If an EIA is undertaken, the EU Directive provides for the right to access information and to participate in the environmental decision-making procedures to the public concerned by the project. If a project creates a significant impact on a Natura 2000 site, the ‘appropriate assessment’ of the infrastructure project could include a public participation process, but this is not mandatory. Similarly, the Floods Directive, the Water Framework Directive and the Maritime Spatial Planning Directive establish public participation processes that may include these projects.

A range of stakeholders could be affected by the construction of breakwaters: for local communities and landowners, hard defences could negatively impact their property. Hard defences can visually disrupt the landscape, affecting tourism interests, recreational users and other sectors. Waterborne activities can also be adversely affected if the installation of hard structures goes wrong.

Success and Limiting Factors

Artificial structures such as breakwaters tend to modify longshore drift, and have adverse effects on adjacent beaches by causing downdrift erosion. In general, to avoid these effects on the coastline, artificial nourishments and/or dune development are often preferable over hard structures unless there are other needs, such as the safe berthing of ships. However, the extent of the blocking of longshore drift, disturbance of adjacent beaches and degradation of landscape values depends very much on the design, orientation of the structure and the main wave/sediment transport direction at the specific site.

Breakwaters provide safe mooring and berthing procedures for vessels in ports. They enhance workability and provide thus higher efficiency in loading and unloading vessels.

Costs and Benefits

Construction costs depend significantly on structure dimensions. Costs can be highly influenced by availability of suitable rocks, transport costs to the construction sites and associated costs of beach nourishment.

In the Netherlands, breakwaters are estimated to cost about EUR 10,000 to 50,000 per running meter (Deltares, 2014).

According to Scottish Natural Heritage, in 2000 construction costs of breakwaters are high – GBP 40,000 to 100000 (50,000-125,000€) – but they require low maintenance; for these structures in particular, beach nourishment costs should be added.

Legal Aspects

The construction of coastal works to mitigate erosion and hard sea defences ‘capable of altering the coast’ fall into Annex II of the EIA Directive (codified as Directive 2011/92/EU): 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. However, this requirement does not affect the maintenance and reconstruction of these works.

Any infrastructure project likely to have a significant impact on a Natura 2000 site must be subjected to an ‘appropriate assessment of its implications for the site’ to determine whether the project will adversely affect the integrity of the site.

The Water Framework Directive calls for the Good Environmental Status of Europe’s water bodies, including coastal waters. Coastal defences could alter the hydromorphological characteristics of coastal waters, for example in terms of water flow, sediment composition and movement, and thus to a deterioration of ecological status. Any projects that do so would need to meet criteria set out in Art. 4 of the Directive. The EU Floods Directive (2007/60/EC) provides a legal framework for flood actions and defence. The construction and restoration of dikes could be part of measures under flood risk management plans. The 2014 Maritime Spatial Planning Directive requires the consideration of the interactions between land and sea, along with maritime activities and adaptation to climate change. Breakwaters could affect these land/sea interactions.

Life Time

Breakwaters have a typical design lifetime of 30-50 years. This is the case for most rock structures.

Further Readings

Scottish Natural Heritage: A guide to managing coastal erosion in beach/dune sy…

VLAAMS INSTITUUT VOOR DE ZEE: Detached Breakwaters

Measure category

Mitigation

EXAMPLE: Early warning system in Sogn og Fjordane (NOR)

nst — Wed, 25 Jan 2017 15:39:06 +0000

EXAMPLE: Early warning system in Sogn og Fjordane (NOR) nst Wed, 01/25/2017 - 16:39

Flood Forecasting and Warning

Based on information from the Climate-ADAPT website.

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.

General description

Sogn og Fjordane is a coastal, mountainous region of Norway that boasts hundreds of thousands of tourist visits annually. Several communities in Sogn og Fjordane are facing numerous hazards such as flooding, avalanches, rock slides and other extreme weather events, that might be exacerbated by climate change. To respond to the challenge an early warning system was developed and tested within a EU research project. The multi-hazard warning system aimed at optimising rescue and other emergency services provided by the county. Due to tourism, it aims to be a cost-effective method reaching all people in the geographic area and not only residents.

A public warning exercise was carried out in 2010 with 2,500 mobile phones receiving the alert as text message and 322 fixed line phones in Aurland received the alert as voice message. The warning exercise was visible on Facebook for 2 hours and received 201,849 viewings. A post-exercise survey was carried out online and a door-to-door survey was conducted in parts of the area to assess the public’s thoughts on the exercise. The population warning exercise was evaluated to measure the efficiency of the warning system by combining an electronic evaluation form and a door-to-door survey.

Key lessons learnt

The project demonstrated how an existing county-encompassing organization could be used to issue the population warning. While the technical aspects of people-centred warning systems are at large readily available, issues concerning confidentiality legislation and system regulations must be solved before successfully implementing efficient location-based warning systems. In order to use social media during crisis situations, the projected concluded that research is needed.

Relevant case studies and examples

Early warning systems

Measure category

EXAMPLE: Floating roads, Hedel (NL)

nst — Mon, 16 Jan 2017 10:17:31 +0000

EXAMPLE: Floating roads, Hedel (NL) nst Mon, 01/16/2017 - 11:17

Combined approach (grey + green)

Removal or relocation

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.

Based on information from the International Intervision Institute

General description

The ‘Floating Roads’ pilot project was implemented in Hedel in the Netherlands. The town of Hedel is prone to flooding due to increasing ground water levels which can lead to the isolation or cutting off of the village and impeded traffic flow. The floating road was designed to be some 70 meters in length and withstand vehicles travelling at speeds of up to 80mph. The town of Hedel in the Netherlands has some 5,000 inhabitant. The small size of the town and the infrastructure of the floating road meant that local authorities and government were central to its planning and implementation.

The design and construction of the road consisted of standard linked units made of aluminium and filled with polystyrene foam to facilitate ‘floating’. These flexible links were secured into the river bed using steel piles and the top layer of the road itself was constructed using typical concrete and non-flexible materials. Aluminium was chosen as a lightweight material that requires little maintenance and is recyclable. Moreover, the standardized units allow for easy transportation and replacement, if necessary. The links between the units provide enough stiffness but also flexibility to withstand changing water levels. The innovative element of the design was the attachment ramps on either end of the floating road. The attachment ramps were stiff structures designed to withstand movement but implemented with a further safety option of a remote controlled moveable bridge should water levels change abrubtly.

The floating road was tested using a normal vehicle under both regular conditions and with incoming waves. The structure performed as expected and the driving experience of the vehicle pilot was not affected by the moving water below. In a simulation test of an emergency situation, a breakdown vehicle went through the same tests and the floating road performed successfully.

Cost-effectiveness and ecosystem-based aspects

Floating and elevated roads are alternatives to bridges and tend to be less expensive. Once constructed, they do not require more maintenance than other types of roads. They are, however, a significant piece of infrastructure and therefore the cost and investment may only be returned once flooding has occurred and been mitigated against.

Floating roads take up less space in terms of construction and infrastructure than traditional roads. They also sit on top of groundwater and therefore do not disturb natural flows and therefore also are likely to minimise pollution.

Key lessons learnt

The main question posed in the pilot construction of the floating road was to understand whether there was added value in having floating roads over conventional roads in order to solve traffic problems that ensue amidst extreme flooding and changing groundwater levels. Floating roads were found to be functional in Hedel and also reduce the amount of disturbed space compared to other options such as a traditional road. For example, generally a road floating on groundwater is 20 meters wide whereas a traditional road at one meter above ground level is 45 meters wide. Cost-efficiency was also considered advantageous to that of building a bridge.

Relevant case studies and examples

Exposed elements elevation

Further Readings

PDF: Floating Road Documentation

Measure category

Mitigation

EXAMPLE: Titchwell Marsh (UK) seawalls and managed realignment

nst — Mon, 16 Jan 2017 08:31:08 +0000

EXAMPLE: Titchwell Marsh (UK) seawalls and managed realignment nst Mon, 01/16/2017 - 09:31

Based on the information available on CLIMATE-ADAPT Platform

Ecosystem based approach

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.

General description

The eastern coast of England is known to have an abundant amount of birdlife, which makes the environmental pressures of sea-level rise and coastal erosion even more concerning. In fact, much of the coast suffers from what is known as a “coastal squeeze” where sea walls and other infrastructure actually prevent the natural mobility of intertidal habitats. The managed realignment strategy at Titchwell Marsh, including seawall reinforcement and intentional breaching, is a response to this.

Through the project, the existing western wall was strengthened, a new wall was constructed, and a breach was made in one of the walls to connect the brackish marsh to the tidal salt marsh in the east, taking into consideration the flow direction and locations of creeks. The sea walls are expected to protect the freshwater ecosystems for the next half century.

The project was supported by several invaluable stakeholders who pushed for action and were critical in achieving all the necessary permits. These stakeholders include:

Natural England (the UK government’s statutory nature conservation advisor)
The Environment Agency (the public body responsible for coastal flood defence)
Eastern Inshore Fisheries and Conservation Agency (the agency responsible for the management of inshore fisheries)
The local community members and Titchwell Marsh supporters

Each of the stakeholder institutions participated throughout the duration of the project and to varying degrees. The local community had the opportunity to attend three consultation events held on separate days. Over 150 people attended these events. Additionally, a yearly newsletter was published to keep concerned local residents and visitors informed of the progress.

Ecosystem-based approach

By creating a breach in the sea wall to connect existing salt marsh creeks, a chain of events can occur that result in significant ecosystem benefits. Seawater is able to enter the brackish marsh and flood it with the tide, turning it into a tidal salt marsh. This new habitat, along with new associated mudflats, is attractive to many coastal bird species, and also serves as a better natural defence against coastal erosion when combined with the sea wall.

However, the loss of brackish marsh can be negative for some species, such as avocet which use the habitat for nesting and breeding. In response to this, additional nesting islands were created in the Titchwell freshwater marshes and new avocet habitats were created at other nearby nature reserves.

A notable side benefit of the project has been the reedbed created in the area excavated for materials for the new sea wall. It is expected that within 10 years of project completion, a full reed bed will have grown in the 2.4ha excavation zone.

Key lessons learnt

Understanding all aspects of the coastal erosion processes impacting Titchwell Marsh led to the design and successful implementation of the most appropriate solution. The decision to include an ecologically strategic breach in the sea wall resulted in several benefits and was an example of working with coastal processes rather than against them.

Time and energy spent involving the local community with consultation and education was also integral to the success of the project. It helped the project gain consent for the various planning requests necessary.

Undertaking construction and excavation work in an environmentally sensitive area is not a quick or easy task. At Titchwell, the wintering and breeding habits of bird species prevented such work from being done for most of the year. Construction was only permitted during August, September and October when disturbance could be minimised. This delayed the overall project and impacted some of the busiest weeks for visitors to the Marsh.

Relevant case studies and examples

Managed realignment

Further Readings

Information from Royal Society for the Protection of Birds (RSPB) website

Measure category

Prevention

Spatial Planning and Integrated Coastal Zone Management (ICZM)

nst — Thu, 10 Nov 2016 12:42:35 +0000

Spatial Planning and Integrated Coastal Zone Management (ICZM) nst Thu, 11/10/2016 - 13:42

Emergency Event and Contingency Planning

Public Awareness and Preparedness

EXAMPLE: A participatory adaptation planning approach, Cascais (PT)

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.

Based on "Papatheochari, Dora (2008): Spatial Planning and Integrated Coastal Zone Management. Available from http://www.coastalwiki.org/wiki/Spatial_Planning_and_Integrated_Coastal_Zone_Management [accessed on 10-11-2016]"

Spatial Planning

Previously, the role of spatial planning focussed intensively on economic and social development. Gradually, environmental dimensions were taken into account, especially through the appearance of sustainable development in environmentally important areas. Spatial planning in Europe promotes environmental sustainability, examining the concept of development which meets environmental, social and economic needs of present and future generations as well as policy and planning instruments to promote such development. It also encourages spatial integration of development perspectives demonstrating how social cohesion, regional innovation and sustainable development can interplay in real planning situations, using policies and planning tools, such as Environmental Impact Assessment and European Spatial Development Perspective.

Through the use of Geographical Information Systems (GIS), spatial planning has been used to define and map coastal and marine areas. It is essential to examine not only environmental impacts of individual activities but to research cumulative effects of multiple activities occurring in an area. Mapping coastal and marine areas in detail allows the opportunity to identify those areas at particular risk from possible pollution or excessive disturbance and to examine in detail how many activities are occurring.

Integrated Coastal Zone Management

Integrated Coastal Zone Management (ICZM) is a dynamic, continuous and iterative process designed to promote sustainable management of coastal zones. ICZM projects cover various geographical areas, from local regions to spatially extensive coastal areas. The “Integrated” in ICZM refers both to the integration of objectives and to the integration of the multiple instruments needed to meet these objectives. ICZM includes the integration of all relevant policy areas, sectors, and levels of administration as well as the terrestrial and marine components of the geographical area under consideration. The word 'Integrated' also refers to four types of integration: spatial, temporal, vertical and horizontal.

Comparing Spatial Planning and Integrated Coastal Zone Management

A common goal of spatial planning and ICZM is to define, develop and protect coastal zones; ICZM is most common at the local scale while spatial planning is often applied at larger scales. Both share policies with the same goal, the resolution of land use conflicts for the development and conservation of coastal and marine environment. Spatial planning at the national level is essential in order to examine the impact of human activities in urban and regional coastal zones. Coastal Zone Management is becoming increasingly necessar because of the increasing importance of coastal and marine exploitation/development and protection.

An enabling environment at the European level could provide the framework in which countries can develop more appropriate integrated coastal zone management policies, including investment strategies, integrated development plans (spatial and functional) and resource management strategies.

The most important issue for both spatial planning and ICZM are the effective and successful implementation of planning systems and policies as well as a better understanding and definition of coastal and marine areas. A common perspective of European coasts must be adopted in order to improve management and planning of activities in coastal and marine areas.

Relevant case studies and examples

EXAMPLE: Developing an Attica Wetland Action Plan (GR)

Measure category

Prevention

Rivers setback leeves

nst — Wed, 02 Nov 2016 13:49:55 +0000

Rivers setback leeves nst Wed, 11/02/2016 - 14:49

Combined approach (grey + green)

Managed retreat

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.

Based on kindly provided information by UNEP's "Green Infrastructure Guide for Water Management: Ecosystem-based Management Approaches to Water-related Infrastructure Projects " (UNEP, 2014)

Along many major rivers, levees have been constructed close to the edge of the river channel, which maximizes the amount of land protected by a levee. By placing levees close to the channel, rivers become more effective conduits for drainage. It can also maximize the use of surrounding lands, even in times of high water levels.

However, levees close to the channel can create a set of problems and challenges. Because they greatly narrow the area available to transport floods, they do work to rapidly flush floodwaters and sediments through the system – but this means that the levees are exposed to high-velocity water along their “wet” side. This can result in erosion and high maintenance costs. In many places, the growing list of sites needing repair has outstripped the maintenance budget, resulting in levees that are more likely to fail during a flood (Leavenworth 2004; American Society of Civil Engineers 2009).

Levees close to a river also dramatically restrict the area of floodplain that benefits from periodic connections with the river and constricts the ability of the river to meander and create new river- floodplain habitats. Because of the vulnerability to erosion mentioned above, these levees often require armouring to prevent erosion and meandering, further diminishing the natural habitat values of the river’s edge, which is generally the most biologically valuable habitat. Also, while levees may prevent flooding at one location, they may increase the risk of flooding upstream and/or downstream of the levees. Moving levees back away from the channel - often called “setback levees” - can alleviate these problems.

Benefits

Setback levees increase channel capacity for carrying floodwaters. By increasing conveyance through a section of river, setback levees can relieve “bottleneck” points on a river where floodwaters would tend to back up and potentially cause flooding.

While levees close to the channel are exposed to deep, high-velocity water during floods, setback levees are less frequently exposed to floodwaters because of the increased channel capacity. Further, because flow over floodplains is generally much shallower and slower than rivers, when setback levees are exposed to floodwaters they are less vulnerable to erosion

Co-benefits

In addition to flood-management benefits, setting levees back increases the area of floodplain exposed to periodic inundation from the river, thus increasing the variety of benefits from river-floodplain connectivity. The expanded area on the “wet side” of the levee provides greater room for the channel to meander and create floodplain habitat features, such as wetlands and forests. During overbank flooding, floodwaters spread out on floodplains and, due to slower water velocities on the floodplain, much of the sediment in transport is deposited there. Because nutrients such as phosphorous are largely adsorbed to sediment particles, this deposition can reduce the loads of sediment and some nutrients in rivers and thus improve water quality for downstream water bodies, such as estuaries and near-shore marine habitats (Noe and Hupp 2005). Biogeochemical processes within floodplain wetlands, such as denitrification, can also reduce nitrogen loads in river water (Burt and Pinay 2005; Valett et al. 2005).

During overbank flooding, a portion of floodwaters can percolate into the shallow groundwater. Portions of the reconnected floodplain can continue to be used for agriculture, with crop selection varying by expected inundation frequency.

Costs

The primary costs for levee setbacks are the removal and construction of levees and, potentially, the purchase of title or easements on the reconnected floodplain. If a levee needs to be replaced or rebuilt anyhow, then the primary costs are for the difference in land area no longer protected by a levee and now prone to periodic flooding. Because the reconnected floodplain can provide habitat and other benefits, conservation funding can be combined with flood-management funding to implement these projects. For example, funds for river restoration were committed to a proposed levee setback project on the Sacramento River in California, USA (Opperman et al. 2011).

Further Readings

Dierauer et al. (2012): Evaluation of levee setbacks for flood-loss reduction, …

Literature sources

American Society of Civil Engineers (2009). Report Card for America’s Infrastructure American Society of Civil Engineers, Washington, D.C.

Burt, T. P. and Pinay, G. (2005). Linking hydrology and biogeochemistry in complex landscapes. Progress in Physical Geography, vol. 29, pp. 297-316.

Leavenworth, S. (2004). Rising risk. Page A1, Sacramento Bee, Sacramento, CA.

Noe, G.B. and Hupp, C.R. (2005). Carbon, nitrogen, and phosphorus accumulation in floodplains of Atlantic Coastal Plain Rivers, USA. Ecological Applications, vol. 15, pp. 1178-1190.

Opperman, J. J., Warner, A., Girvetz, E. H., Harrison, D. and Fry, T. (2011). Integrated reservoir-floodplain management as an ecosystem-based adaptation strategy to climate change. Proceedings of American Water Resources Association 2011 Spring Specialty Conference on Climate Change and Water Resources. American Water Resources Association, Baltimore, Maryland.

Valett, H.M., Baker, M.A., Morrice, J.A., Crawford, C.S., Molles, M.C., Dahm, C.N., Moyer, D.L. and Thibault, J.R. (2005). The flood pulse in a semi-arid riparian forest: metabolic and biogeochemical responses to inter-flood interval. Ecology, vol. 86, pp. 220- 234.

Scale

Local

Regional

Measure category

Prevention

Flood and hazard forecasting

giacomo.cazzola — Thu, 15 Sep 2016 12:13:22 +0000

Flood and hazard forecasting giacomo.cazzola Thu, 09/15/2016 - 14:13

Flood Forecasting and Warning

Based on: Jha, Abhas K., Robin Bloch, and Jessica Lamond. Cities and Flooding: A Guide to Integrated Urban Flood Risk Management for the 21st Century. World Bank Publications, 2012.

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.

Different flood forecasting service models exist based on the needs of end users: a system may be developed for the public or strictly dedicated to the authorities. There is no single consistent approach worldwide but the basic principles of a good warning system are shared by all. These comprise:

Better detection in times of need well before the actual event occurs
Interpretation of the detected phenomena and forecasting this to the areas likely to be affected
Dissemination of the warning message to the relevant authorities and public via the media and other communication systems.

The fourth and final aspect is to encourage the appropriate response by the recipients by preparing for the upcoming event. This can be improved through flood response planning by people at risk and their support groups.

Uncertainty in flood forecasting

Models, by definition, are approximations of reality. As described earlier, all models suffer from a certain level of approximation or uncertainty in spite of powerful computing systems, data storage and high level technologies. Decision makers have to consider the effects of uncertainties in their decision-making process. Errors in forecasting of an event, for example stage or time of arrival, may lead to under-preparation (at the cost of otherwise avoidable damage) or over-preparation (resulting in unnecessary anxiety). The balance between failure to warn adequately in advance and the corrosive effects of too many false alarms must be carefully managed.

The reliability of flood forecasting models relies on the quantification of uncertainty. All natural hazards are uncertain. The various sources that give rise to uncertainty in forecasting and early warning can be classified (Maskey. 2004) as:

Model Uncertainty
Parameter Uncertainty
Input Uncertainty
Natural and Operational Uncertainty.

It is necessary to gain a better understanding of the options available to deal with the uncertainties within the system arising from these different sources.

In order to produce a forecast, the initial conditions are typically determined by means of observations from rain gauges; these may, however, be unevenly spaced throughout the catchment, leading to uncertainty as to the total volume of rainfall. Where hydrologically important areas (such as steep slopes) are unrepresented, the model may utilize an interpolation method (introducing another element of uncertainty) in order to estimate run-off volume and peak flows. More sophisticated modeling can address these issues, but this in turn may demand high processing speeds and lengthy run-times.

To offset some of this uncertainty, operational flood forecasting systems are moving towards Hydrological Ensemble Prediction Systems (HEPS), which are now the ‘state of the art’ in forecasting science (Schaake et al. 2006; Thielen et al. 2008). This method formed part of initiatives such as HEPEX (Hydrological Ensemble Prediction EXperiment) which investigated how best to produce, communicate and use hydrologic ensemble forecasts for short, medium and long-term predictions. Despite its demonstrated advantages the use of this system is still limited: it has been installed on an experimental basis in France, Germany, Czech Republic and Hungary.

To deal with the uncertainty in spatio-temporal distribution and prediction of rainfall for extreme events, especially through radar derived data, a promising approach has been to combine stochastic simulation and detailed knowledge of radar error structure (Germann et al. 2006a, 2006b, 2009; Rossa et al. 2010). Radar ensembles have the potential benefits of increasing the time for warning especially for flash floods (Zappa et al. 2008). Advanced techniques, such as disdrometer networks (equipment capable of measuring the drop size, distribution and velocity of different kinds of precipitation) and LIDARs are being used to capture small scale rainfall phenomenon, whilst satellite remote sensing is more appropriate for regional and global level applications. A combination of all these methods and blending information is considered to be the most promising way forward.

There are a several useful examples of such systems:

DELFT-FEWS: one of the state of the art hydrological forecasting and warning systems developed by Deltares. This system is an integration of a number of sophisticated modules specialized in their individual capacities and the system is highly configurable and versatile. The system can be used as a standalone environment, or it can be used as a compliant client server application. Through its advanced modular system FEWS has managed to reduce the challenges like handling and integration of large datasets to a considerable extent.
Automated Local Evaluation in Real Time (ALERT) is the method used within the AUG member states to transmit data and information using remote sensors for warning against flash floods.
Central America Flash Flood Guidance is an example of regional flash flood warning. The national Hydrologic Warning Council (NHWC) has member countries across North America and many parts around the world; it is also a major organization in data dissemination for early warning for flood events.
The Mekong River Commission flood forecasting system, discussed above, has been operating since 1970. It is an integrated system which provides timely forecasting to its member countries. It consists of three main systems of data collection and transmission, forecast operation and information dissemination at both national and regional level.
The Southern African regional model for flood forecasting Stream Flow Model (SFM) has been applied after the Mozambique flood in 2000. The USGS along with Earth Resource Observation System (EROS) supports monitoring and modeling capacities of Southern African Countries.
Regional Water Authority of Mozambique (ARA-Sul) is responsible for issuing flood warning and real time forecasting. The system is operational in Southern Africa with a mean area of 3,500 square kilometers. A simplified flood warning system, the Mozambique Flood Warning Project, is specially tailored to the needs of the local population. It also involves the local people and trains them to install, monitor and maintain the structures.
Hydro Met Emergency Flood Recovery Project is used in Poland.
Bhutan’s Glacial Lake Outburst Flood (GLOFs) Iridium Satellite Communications is used as the telemetry back-bone for Bhutan’s GLOF Early Warning Project.
In the Toronto region of Canada, the Toronto and Region Conservation Authority (TRCA) flood forecasting and warning system is used; this is a scalable flood warning system including web-based data and video for nine watersheds.
The Automatic Dam Data acquisition and alarm reporting system, is the Puerto Rican System to obtain, monitor and analyze, in real- time, critical safety parameters such as inflows, outflows, gate openings and lake elevations for 29 principal reservoirs
Central Water Commission (CWC) in India provides the Turnkey Flood forecasting system across 14 states having 168 remote sites in six river basins.

Literature sources

Maskey, S., Guinot, V. and Price, R.K. 2004. “Treatment of precipitation uncertainty in rainfall-runoff modeling: a fuzzy set approach.” Advances in Water Resources 27 (9): 889-98.

Schaake, J., Franz, K., Bradley, A., and Buizza, R. 2006. “The Hydrological Ensemble Prediction Experiment (HEPEX).” Hydrological and Earth System Sciences Discussions 3: 3321–32.

Thielen, J., Schaake, J., Hartman, R. and Buizza, R. 2008. “Aims, challenges and progress of the hydrological ensemble prediction experiment (HEPEX) following the third HEPEX workshop held in Stres 27-29 June 2007.” Atmospheric Science Letters 9: 29-35.

Germann, U., Berenguer, M., Sempere-Torres, D., and Salvadè, G. 2006a. “Ensemble radar precipitation estimation — a new topic on the radar horizon.” Proceedings of the 4th European Conference on Radar in Meteorology and Hydrology (ERAD). Barcelona. September 18–22, 2006. 559–62.

Germann U., Galli, G., Boscacci, M, and Bolliger M. 2006b. “Radar precipitation measurement in a mountainous region.” Quarterly Journal Royal Meteorological Society 132: 1669–92.

Germann, U., Berenguer, M., Sempere-Torres, D., and Zappa, M. 2009. “REAL — Ensemble radar precipitation estimation for hydrology in a mountainous region.” Quarterly Journal Royal Meteorological Society 135: 445–56.

Rossa, A. M., Cenzon, G. and Monai, M. 2010. “Quantitative comparison of radar QPE to rain gauges for the 26 September 2007 Venice Mestre fl ood.” Natural Hazards and Earth System Science 10 (2): 371–7.

Zappa, M., Rotach, M.W., Arpagaus, M., Dorninger, M., Hegg, C., Montani, A., Ranzi, R., Ament, F., Germann, U., Grossi, G., Jaun, S., Rossa, A., Vogt, S., Walser, A., Wehrhan, J., and Wunram, C. 2008. “MAP D-PHASE: Real-time demonstration of hydrological ensemble prediction systems.” Atmospheric Science Letters 2: 80–7.

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Evacuation planning

giacomo.cazzola — Thu, 15 Sep 2016 11:39:02 +0000

Evacuation planning giacomo.cazzola Thu, 09/15/2016 - 13:39

Emergency Event and Contingency Planning

Based on: Jha, Abhas K., Robin Bloch, and Jessica Lamond. Cities and Flooding: A Guide to Integrated Urban Flood Risk Management for the 21st Century. World Bank Publications, 2012.

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.

Organizational aspects of evacuation planning

An interdisciplinary planning organization must be set up covering the key institutions that have remits relating to disaster and specifically flood management. This organization can be a Community Flood Management Committee (CFMC). In addition to the CFMC, evacuation centers should also be established in appropriate settlements.

The members of the CFMC should have knowledge of evacuation and rescue operation and emergency, including medical care (if this is not the case, then basic training should be provided to them). Evacuation plans should be prepared after discussion with the community. Participatory planning will increase people’s awareness and ability to cope and manage flood risk. The evacuation plan should be available to all members of the community, including the most vulnerable.

Dissemination of information on flood risk and flood preparedness requires the organization of regular community meetings. Such meetings can take place before the onset of the rainy season, or monsoon. It is vital that evacuation drills will be held regularly to test the effectiveness of the evacuation plans.

The evacuation plan should delineate an escape route and also identify small- scale works that may be needed to make the route safer. Such works can be executed in cooperation with the community as well as with external support. The evacuation plan should also determine modes of transport and access routes for evacuation and rescue operations and relief projects. In addition, the evacuation plan should identify open spaces and buildings to be used as evacuation centers. These can function as described by Arnold, Chen, Deichmann et al. (2006: 149).

Temporary shelters and refuges
Hospitals, possibly in existing buildings with stored supplies and basic medical equipment
Information centers, with uninterrupted linkages to the central communications system
Supply distribution points for basic survival supplies, such as water, food, and blankets
Sanitary facilities, including toilets, showers, and waste disposal units.

To develop evacuation plans and carry out the tasks outlined above, maps showing the most exposed areas to flood risk should be available. EWS should also be in place to give advance notice of an impending flood allowing evacuation plans to be put into action. Even when a flood is not as severe as predicted, these preparations help test evacuation plans and inform the communities as to the nature of flood risk.

Provision of flood shelters and refuges

As stated in UNDP (2009:36): “Shelter is likely to be one of the most important determinants of general living conditions and is often one of the largest items of non-recurring expenditure.”

Shelters and refuges must, as a minimum:

Provide protection from the climate conditions
Provide space to live and store personal belongings
Ensure dignity, privacy, safety and emotional security.

In most emergencies there is a common basic need for shelters or refuges. However, issues such as the type and the design of the shelter, the required materials, by whom it is constructed, and the duration it is expected to last, will vary significantly according to the situation. Vulnerability analysis can identify the basic needs and priorities of the affected population in relation to shelters. Safe areas for flood shelters or refuges may include:

Schools
Religious meeting places (such as temples, churches, mosques)
Community centers
Higher ground (such as roofs, upper floors, embankments)
Military installations
Barracks.

Location and size of shelters and refuges

The need for the location and size of shelters and refuges needs to be decided in consultation with the communities. Transportation between the shelters and social and work locations for the displaced population should be considered. Existing social practices, and the provision and maintenance of shared resources (such as water, sanitation facilities and cooking) should be taken into consideration in the design of shelters and also in the allocation of space within shelters and plots. The plot layout in the evacuation centers must preserve the privacy and dignity of individual households.

The use of materials and the type of shelter that are most commonly used among refugees or the local population is to be preferred for the construction of shelters. The design of the shelter must follow the simplest principles and structures. The provision of a solid and robust roof is the main requirement, and even when a complete shelter cannot be provided, adequate roofing should always be the priority.

Plastic tarpaulins can be easily found in most cases. Tents are not always the best type of shelter because it is not easy to live in them and also they cannot provide adequate protection against extreme climate conditions. Nevertheless, in certain cases, tents may be used as storage facilities, or to set up hospitals, schools and other facilities. The success of the evacuation centers highly depends on these facilities.

Communications between shelters and refuges

The success of an evacuation plan is highly dependent on the efficacy of the communication systems. Established communication systems must ensure that the relevant authorities are promptly informed, for example by radio or telephone. The sharing of information is essential to achieve a better understanding of the problems. Coordination among all those involved in an evacuation operation is necessary to assure that the evacuation plan is being implemented successfully.

Key lessons learnt

Evacuation plans minimize the risks and impacts of flooding for the population of cities and towns.

Relevant case studies and examples

EXAMPLE: London Mass Evacuation Framework (UK)

Literature sources

Arnold, M., Chen, R.S., Deichmann, U., Dilley, M., Lerner-Lam, A.L., Pullen, R.E. and Trohanis, Z. ed. 2006. Natural Disaster Hotspot Case Studies. Washington, DC: World Bank Hazard Management Unit.

UNDP (United Nations Development Program). 2009. Emergency Relief Items, Compendium of Generic Specifi cations. Geneva: UNDP.

Measure category

Early warning systems

giacomo.cazzola — Thu, 15 Sep 2016 11:06:41 +0000

Early warning systems giacomo.cazzola Thu, 09/15/2016 - 13:06

Flood Forecasting and Warning

Based on: Jha, Abhas K., Robin Bloch, and Jessica Lamond. Cities and Flooding: A Guide to Integrated Urban Flood Risk Management for the 21st Century. World Bank Publications, 2012.

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.

Warning systems can be used to alert relevant authorities or the public or both. The scale of a warning system can be national, based on a river basin, or local and run by volunteers. Most are stand-alone national operations, but warning systems have been developed covering several international rivers, such as the Rhine, Danube, Elbe and Mosel in Europe, the Mekong, Indus and Ganges-Brahmaputra-Meghna basins in Asia and the Zambezi in Southern Africa (United Nations 2006). However, the utility of EWS is crucially dependent on the underlying forecasting system, the quality of emergency plans and the level of preparedness of the community at risk. The quality of forecasting is also dependent on the nature of the hazard. Warning systems related to river flooding have a longer lead time than those for cyclonic events; seismic induced tsunamis may have very short warning periods. Forecasting flash flooding is also very problematic; this has implications for developing nations which are more exposed to such risks, due to the prevalence of monsoon type flooding. Whilst there is general agreement about the desirability of EWS, the implementation of such a system is necessarily subject to local factors.

Essentials for an effective EWS

The four main essentials for any flood warning system are:

Detection of the conditions likely to lead to potential flooding, such as intense rainfall, prolonged rainfall, storms or snowmelt
Forecasting how those conditions will translate into flood hazards using modeling systems, pre-prepared scenarios or historical comparisons
Warning via messages developed to be both locality- and recipient-relevant and broadcasting these warnings as appropriate
Response to the actions of those who receive the warnings based on specific instructions or pre-prepared emergency plans

Failure in any one of the four key elements of an EWS will lead to a lack of effectiveness. Inaccurate forecasts may lead to populations ignoring warnings issued subsequently.

The lack of clear warning and instruction may have resulted, for example, in the deaths of people escaping the Big Thompson Canyon flood in the US in the 1970s. Without clear instructions many people were killed trying to drive out of the canyon rather than taking the safer option of abandoning cars and climbing to higher ground.

Finally, the case of Hurricane Katrina demonstrated the scenario where clear advanced warnings failed to protect the population because the evacuation planning was inadequate.

Organizational aspects of flood warning dissemination

There are multiple communication channels by which a flood warning may be broadcast and the choice of media will vary depending on the intended recipients. It is also essential to consider the use of media that will be robust to the impacts of a flood.

The most successful warning services use a combination of media, ideally with consistent messages and timescales, as well as the response the message hopes to initiate. For example, an individuals whose home is likely to be flooded will probably react best to a personal message either via phone, fax or in person; people who should avoid travelling to or through an affected area may prefer a news bulletin backed up by an internet or press map of the affected area.

Costs and resources

Setting up a warning system may be a low cost option for countries and is often seen as the first line of defense for that reason. The cost will be lowest in nations with existing and adequate forecasting and monitoring services. In this case the setting up of a warning center can be a very low cost process and this can be quickly established during consultation and stakeholder identification.

Setting up adequate forecasting and monitoring serviced can require much larger investments in expertise, software and hardware for modeling and monitoring equipment. The lead time to establish forecasts of the required reliability and timeliness may be a deterrent.

Key lessons learnt

Once established the service will require continuous investment in manpower, data and other resources in order to be functionally useful. Recruitment and retention of qualified personnel, continuity of funds and operations and maintenance of monitoring, modeling and dissemination equipment can be key challenges in the long term sustainability of systems. This can be particularly acute for low frequency events.

Relevant case studies and examples

EXAMPLE: Early warning system in Sogn og Fjordane (NOR)

Literature sources

United Nations. 2006. Global survey of early warning systems. UN.

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