Local

Measure category

Combination of groynes and beach nourishment, Clacton (UK)

nst — Mon, 16 Jan 2017 12:30:37 +0000

Combination of groynes and beach nourishment, Clacton (UK) nst Mon, 01/16/2017 - 13:30

Erosion

Hold the line

Article about the measure in the East Anglian Daily Times

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.

Based on information from the Tendring Destrict Council.

General description

The beach area at risk is five kilometers long and runs from Clacton Pier to Holland Haven in Essex on the east coast of England. The project involves using 23 fishtail rock groynes, each 90 meters long and 220 meters apart, and adding roughly 950 000 cubic meters of sand and shingle beach material to the coastline

The project is the biggest of its kind to ever be undertaken by the Tendring District Council. It was approved by the UK Environmental Agency in 2013 and costs roughly 36 million pounds, with support from several funding organizations.

The groyne and beach recharge activities were effective, on time, and on budget. The materials for the rock groynes were made up of the crushed materials from the existing structures and new smaller rocks from a quarry, and were covered by a geotextile once in place in the sea. Larger rocks were placed on the geotextile and the groynes were designed in a fishtail style. The fishtail design of the groynes was chosen to allow dual protection, with the bigger arm blocking waves from the North Sea and the little arm blocking waves from Kent. The materials for beach recharge came from a licensed dredge site and was made up of sand and shingle (a mix of sand, gravel and cobbles, mimicking the natural beach material of the area. During high tide, a dredging ship would pump this mix through a pipe onto the beach, forming an 18 metre wide crest about one metre below the promenade walking level.

Key lessons learnt

Pumping the sand and shingle mix early in the project towards the shore created a platform to help construct the many fishtail rock groynes and support the heavy construction machinery used on the beach during construction. Even with all the groynes, periodic beach re-profiling will be necessary in the future due to coastal processes.

Relevant case studies and examples

Groynes

Further Readings

Scale

Measure category

Coastal floods or storm surges

EXAMPLE: Artificial Island - Amager Beach, Copenhagen (DK)

nst — Wed, 07 Dec 2016 08:37:02 +0000

EXAMPLE: Artificial Island - Amager Beach, Copenhagen (DK) nst Wed, 12/07/2016 - 09:37

Erosion

Move seaward

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.

Amager Beach is an artificial island in the southern part of Copenhagen. It was built from 1.5 million cubic meters of raw material, mainly because the old beach had “required almost annual additions of sand to keep it from disappearing into the shallow waters of the Baltic channel” (Cohen 2010: 124). Now, it is a recreational area, which can be used all year round. The island is 2 km. long and the lagoon is 400 m. at its widest point. In the northern part of the island, a more natural landscape with sand dunes can be encountered. In the south more park-like elements are installed. There are facilities for playing beach volley, surfing, flying kites or swimming. It is very clear that the simple concept of the Beach Park and its unique features provide a great setting for continued development of activities and architecture in the area (HOGK 2013). “In its new locale, Amager Beach is self-preserving because the waves are large enough to pull the sand both onto and away from the beach” (Cohen 2010: 124).

Between 2004 and 2005 the island was built and the city of Copenhagen invested 25 million euros to develop a piece of ‘engineered nature’. The project was based on an open dialogue with various stakeholders: focus groups, interest organisations and local users were involved in a continuing effort to develop the project’s qualities (HOGK 2013). This is an example of how water attracts resourceful residents and businesses, making this area an attractive address in Copenhagen (State of Green). It shows that ecosystem based approaches can be very cost-effective.

Relevant case studies and examples

Land claim

Literature sources

Cohen, Nevin (2010): Green Cities. An A-to-Z Guide. SAGE Publications, 576 p.

State of Green (2015): Rethinking urban water for new value in cities. https://stateofgreen.com/files/download/7899

HOGK (2013): Amager Beach. In: Landezine (http://www.landezine.com/index.php/2013/01/amager-beach-by-haslov-and-kjaersgaard/)

Scale

Measure category

Protection

Rivers setback leeves

nst — Wed, 02 Nov 2016 13:49:55 +0000

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

Managed retreat

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)

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.

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

Regional

Measure category

Health planning and awareness campaigns

giacomo.cazzola — Thu, 15 Sep 2016 10:31:39 +0000

Health planning and awareness campaigns giacomo.cazzola Thu, 09/15/2016 - 12:31

Flash floods

Coastal floods or storm surges

Urban floods

Public Awareness and Preparedness

Non-structural measure

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.

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.

Floods can make it difficult to maintain dignity and hygiene, and lead to an increase in the risk of disease in the following ways:

Widespread contamination by fecal material due to destruction, breakage or damage to sewage systems and latrines, and subsequent open defecation
Contamination of drinking water
Thick layers of silt, debris and other materials
Loss or lack of key hygiene item
Standing pools of contaminated water or sewage
Rotting corpses (human and animal) can lead to excessive fly breeding or contamination of water sources from insect feces
Increase in vector breeding
An adverse psychological impact due to loss, and a sense of despair.

An effective health awareness campaign will provide clear timely advice on how best to protect individual and public health during a flood and will facilitate a two–way dialogue such that feedback from the affected persons directly informs priorities and decision making.

Pre-flood campaigns are vital for risk mitigation and preparedness. Campaigns during, or post-flooding, will reinforce messages and mobilize communities into action to preserve public health.

Key Components of Health Awareness Campaigns

Urban residents may have received little or no previous hygiene education or health awareness training and are likely to be ill-prepared to respond to a flood. When this condition is combined with weak local or municipal government and staff who are themselves ill-prepared, a flood event can result in a complete breakdown of basic public services (water, sanitation and solid waste management) alongside a significant increase in the risk of accidents and disease. As a consequence, even a relatively minor flood can result in a dangerous increase in morbidity and mortality.

It is important to plan health awareness campaigns with an understanding of the type of flooding involved, its anticipated effects, probable duration and the likely impact on the urban population. This planning also has to take into account the current status of public understanding and awareness of health issues, as no two urban situations will be the same. Both the messages and modes of communication should be adapted for the particular situation and for different audiences. The messages should take account of beliefs and attitudes that regarding health, disease and hygiene and should appeal to the interests and priorities of different groups.

The health awareness interventions should be designed with participation and collaboration of all key stakeholders, to ensure that effective messages are developed, and that both clarity and consistency apply to the communication strategy. The relevant government ministries (such as environmental health, social welfare, health, education) should be involved, as well as influential leaders, opinion formers and agencies working in the WASH (the now commonly used acronym used for water supply, sanitation and hygiene promotion) or health cluster. Different sections of the community should participate, including the more vulnerable groups such as low-income groups, women, children, aged and disabled people.

Health awareness is required by three distinct groups of people:

Municipal staff, volunteers and health professionals
The general public and in particular vulnerable groups
Media workers.

When and where to use Health Awareness Campaigns

Any flood-prone city or town would be well advised to invest in a health awareness campaign, both pre-flood and post-flood, irrespective of what type of flood is anticipated. An assessment in advance of the likely public health risks during a flood in that location (including, for example, impacts on water treatment works, or probable disease vectors where appropriate) will guide the design and prioritization of any campaign to make it more cost effective.

Benefits

An effective public health campaign will reduce death and disease caused by flooding. Specifically, pre-flood health awareness campaigns will:

Develop knowledge, understanding and build the capacity of municipal staff and volunteers to work effectively and efficiently post-flood, to preserve public health and reduce mortality and morbidity.
Provide guidelines on key elements of an initial rapid assessment of public health risks and build capacity to institute an appropriate, rapid and coordinated WASH response.
Protect health service capacity from the impacts of flooding.
Post-flood campaigns will help preserve personal and public health by giving the public immediately relevant knowledge and awareness to complement the hardware relief interventions.

The health and hygiene information is also applicable in non-flood situations and, as such, will have a knock-on effect of improving public health in general. Health awareness campaigns to deal with urban floods sit very comfortably alongside other, more traditional, health campaigns such as mother and child health, anti-malaria and HIV/AIDs awareness. The same professional staff and volunteers can and should be involved.

Risks and weaknesses

There are few risks associated with promoting health awareness in urban areas prone to flooding. The challenge is to ensure that this is carried out effectively, as far in advance of floods as possible and in close coordination with the structural mitigation and relief interventions.

Cities may face particular challenges, such as providing sanitary excreta disposal options for low income settlements, or maintaining waste disposal services during the flood. Given the relative poverty of many affected municipal authorities and local governments, there may also be issues around obtaining resources to invest in public health flood preparedness, when structural interventions could appear more politically advantageous.

Essentials and key considerations

The affected population should be made aware of their rights and entitlements to relief and recovery operations; this is particularly relevant to the rights to protection for specific groups of persons (such as internally displaced persons; women, children and adolescents; the aged; people living with HIV/AIDs; persons with disabilities; single parent households; ethnic and religious minority groups; and indigenous peoples). IASC (2008) discusses these issues in more detail.

Public health campaigns can only provide knowledge and understanding, which may do little practical good without tangible interventions such as provision of clean drinking water, chlorine tablets or safe waste disposal sites. However, as stressed in this section, without pre- and post-flood ‘soft’ interventions (specifically aimed at promoting awareness of how to preserve health and hygiene during floods), the ‘hard’ interventions are unlikely to be effectively mobilized or, even if mobilized, will by themselves be of minimal use.

Catastrophic outbreaks of diseases are not inevitable after a disaster: they do not spontaneously occur. However, the keys to preventing disease are to be prepared, to educate and motivate both the appropriate officials and the public, and to promote the meeting of basic sanitary needs.

Literature sources

IASC. 2008. Human rights and Natural Disasters, Operational Guidelines and Field Manual on Human Rights Protection in Situations of Natural Disaster.

Scale

Public Awareness and Preparedness

Regional

Measure category

Preparedness

Public Participation Approaches in Implementing DRR Measures

nst — Mon, 12 Sep 2016 09:51:58 +0000

Public Participation Approaches in Implementing DRR Measures nst Mon, 09/12/2016 - 11:51

Non-structural measure

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.

Based on: Firus et al (2011): Planning and implementing communication and public participation processes in flood risk management.

These findings are based on a handbook that was published as a result of the project ‘Integrative flood risk governance approach for improvement of risk awareness and increased public participation`(IMRA). The overarching goal of the IMRA project was to influence and change risk perception and real decision-making by actively involving stakeholders and the public in three case study areas of three different river basin districts in Europe. This handbook aims to provide an innovative tool to support in planning, implementing and evaluating a communication and public participation process as part of Flood Risk Management. The active involvement of all interested parties is also stated in the EU Floods Directive (2007).

12 Steps

The described concept is composed of 12 Steps, following a logical and chronological order (see Firus et al. 2011: 8).

Identify your own position

Step 1: Carry out initial self assessment of risk governance performance
Step 2: Define goals and scope of process
Step 3: Identify resources (money, time, personnel)

Identify your strategic partners

Step 4: Identify relevant stakeholders
Step 5: Design and define scope of participation process
Step 6: Create a network of stakeholders
Step 7: Identify the public’s view

Decide on measures

Step 8: Agree on objectives
Step 9: Agree on targeted communication and participation measures
Step 10: Design an implementation plan for communication and participation measures

Implementation

Step 11: Implement communication and participation measures

Evaluation

Step 12: Evaluate the process

The handbook fleshes out the different steps, for example how to select proper stakeholder for participatory processes (in Step 4), describing in more detail what kind of roles stakeholder can take (in Step 5), or how to deal with different social milieus (Step 9).

Methods

In the second part of the handbook, innovative and well-proven communication and participation methods are presented. Within the project, these have been highly suitable for a communication and participation process in flood risk management. The authors describe 16 different methods with respect to their purpose, area of application, aim of the method and context, target group, scale of application, costs, necessary skills, expected results, assessment of results, or key references.

As one example of methods, the world café is described here in more detail. The World Café method is quite well established and its main aim is that people get in contact with each other, discuss and develop new ideas by the power of networking with a multitude of people. It can be used for strategic dialogue, multi-stakeholder engagement, multi-generational collaboration and cooperative action. Participants are seated on Café-style tables and are encouraged by the table host to write, doodle and draw key ideas on their tablecloths. Several rounds of the tables can be undertaken. Finally a period of sharing discoveries and insights in a whole group sums up the initiative.

Key lessons learnt

Practical recommendations when planning and implementing a communication and participation process:

Make a priority list and tackle the most important issues first.
Make people feel concerned: they must understand that DRR is something that really is relevant for them and not just an administrative exercise.
Involve people emotionally (positively!), e.g. by involving witnesses. But: do not make people afraid but raise awareness.
Choose the right method for the respective target group as people have different social backgrounds and act in different social networks.
Provide some striking/prominent examples/people.
Be aware that your manpower and money are limited resources; the effectiveness of measures is important.
Evaluate your communication material and public participation methods.

Relevant case studies and examples

EXAMPLE: Public participation in dyke construction, Timmendorfer Strand (GER)

Further Readings

Project IMRA

Literature sources

Katja Firus, Mark Fleischhauer, Stefan Greiving, Patrizia Grifoni, Therese Stickler (2011): Planning and implementing communication and public participation processes in flood risk management. Published in the joint project IMRA - Integrative flood risk governance approach for improvement of risk awareness and increased public participation. (http://www.partizipation.at/fileadmin/media_data/Downloads/Zukunftsdiskurse-Studien/imra_handbook.pdf)

European Parliament and the Council of the European Union (2007): Directive 2007/60/EC of the European Parliament and of the Council on the Assessment and Management of Flood Risks, published in the Official Journal (OJ L 288) on 6 November 2007.

The World Café (2015): Quick Reference Guide for Hosting World Café. Online: http://www.theworldcafe.com/wp-content/uploads/2015/07/Cafe-To-Go-Revised.pdf

Scale

Individual - private

Measure category

Public Awareness and Preparedness

Multi-Criteria Analysis (MCA)

nst — Mon, 12 Sep 2016 09:45:39 +0000

Multi-Criteria Analysis (MCA) nst Mon, 09/12/2016 - 11:45

Non-structural measure

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.

Based on the RISC-KIT Results on MCA and RISC KIT Deliverable 4.2 – Evaluation of DRR plans.

General description

MCA methodologies have been widely applied in environmental studies as they have proven useful tools when assessing performance of options against criteria that are difficult to quantify and involve qualitative aspects. In RISC-KIT, MCA is used in three ways: 1) as a way facilitate the communication and presentation of project results in a coherent and contextualized manner to relevant local stakeholders and decision-makers; 2) as a way to capture other types of knowledge, such as local every-day experiences, socio-economic and political factors that might affect how the proposed measures are perceived; and 3) as a way of facilitating interaction between local stakeholders and raising awareness of risks and potential measures.

Results from the implementation of the MCA in RISC-KIT cases highlights several key lessons for future DRR projects with regards to a) the importance of sufficient preparation for participatory sessions; b) stakeholder interaction and inclusion in the DRR projects; c) the way research results are presented to non-research communities; d) and the challenges of implementing single-approaches to diverse contexts.

In RISC-KIT MCAs are used to decide, among many options, which is the most convenient for most stakeholders in terms of a set of criteria (i.e. in flood and coastal risk management decisions can involve the construction of a flood alleviation channel or dredging a river, or harder engineering solution like the construction of barriers or dams). For RISC-KIT, an own MCA methodology is used to evaluate DRR strategies with respect to criteria that capture the key dimensions of the decision-making problem, involving human judgment and preferences (Saarikoski et al. 2015). MCA is about determining the extent to which options create value by achieving objectives, identify the areas of greater and lesser opportunity, prioritize the options, clarify the differences between the options, and help the key players to understand the situation better. Ultimately the use of the MCA in the project would allow each case study to test assumptions on the dynamics between DRR measures, between these measures and the specific social contexts, as reaction and responses from local actors to these measures. Outweighing different DRR measures in different contexts implies that different criteria need to be considered in order to assess which option is the best, for whom, for what, and when.

Selection of criteria

Criteria have been selected based on a literature review of the most important factors when contemplating, planning, financing, and implementing DRR measures. Studies identify factors such as social acceptance, political will, availability of financial resources and technological know-how, as crucial for increased investments in DRR measures (Davis et al. 2015). For the MCAs in RISC-KIT, three main categories of criteria were selected: Feasibility, Acceptability, and Sustainability. Feasibility refers to that (human, technical, time, and financial) resources required to implement the measure are available or can be acquired, whether the proposed measures address underlying concerns in society, whether the proposed location for implementing the measures is suitable for local needs and plans, and whether the proposed measure could have positive or negative impacts (e.g economic) to society at large. Acceptability refers to the expectations of stakeholders and recipients in the case studies sites. These actors may include civil society, interest groups, and influential individuals in society. Sustainability addresses the relevance of the measures in the present and future, its impact upon human activity and ecosystems, and the resilience of the measures to future changes.

MCA Steps in RISC-KIT

The MCA was carried in a workshop format and consisted of five steps:

Interactively present preliminary DRR measures from model results and agree on Strategic Alternatives: The MCA carried out in RISC-KIT was informed by the results produced through the Bayesian Network regarding the effectiveness of DRR measures to coastal risks. Through the use of the interactive materials, stakeholders were able to learn how the different measures behaved in light of different risk scenarios and their effectiveness in preventing coastal hazards like floods and erosion. Hereon, stakeholders had the possibility to collectively agree on the Strategic Alternatives (i.e., combinations of measures) that would be scored in the MCA
Score measures against criteria: Stakeholders assessed the performance of each Strategic Alternatives (SA) against criteria (e.g. how feasible/sustainable/acceptable/suitable are sand dunes as a measure to prevent coastal erosion in your area?) by first assigning a value ranging between -2 and +2, to each criterion per SA, on an individual basis. Once stakeholders had assigned all scores, they used colored post-it’s with pre-assigned values (-2 to +2) to write their individual scores once again, but this time make them public to the other stakeholders by pasting in a MCA flip chart. Once all scores were visible, stakeholders could engage in a facilitated discussion and agree on one score per criteria. In those cases where consensus could not be reached, individual scores were instead averaged.
Weigh criteria: to indicate criteria’s importance relative to the objective of the process (e.g., what criterion is most important to consider if sand dunes were to be implemented to reduce coastal erosion?). This was done through 2 main steps: first, stakeholders were handed out 8 stickers each which needed to be distributed on an individual basis in between the three criteria to indicate their importance. The more stickers a criterion received the heavier its weights. The second step took place once stakeholders had assigned individual weights. Each participant indicated the individual weights on the MCA flip chart so that they would be visible to the group. Thereafter the group engaged in a facilitate discussion to agree on a weight per criteria. Equal weights could be given to more than one criterion; however, it is common in MCA to give different weightings to different options, reflecting their importance in the overall objectives. In those cases were consensus was not reached, weights were averaged. Criteria were only weighted once, as it is assumed that their importance is constant across all SAs.
Calculate weighted scores of criteria: for each measure by multiplying scores times the weight for each criterion for all measures.
Generate sums per measure by adding the weighted scores for all criteria per SA and entering the total value in the row titled “SUMS” at the end of the MCA Matrix. The SA will the highest weighted scores was stakeholders’ preferred alternative. Picture 1 shows an example of a complete MCA.

Scale

Measure category

Temporary and demountable flood defences

giacomo.cazzola — Thu, 08 Sep 2016 14:04:11 +0000

Temporary and demountable flood defences giacomo.cazzola Thu, 09/08/2016 - 16:04

Flash floods

Coastal floods or storm surges

Natural flood, runoff, catchment management

Hold the line

Grey infrastructure

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).

Based on kindly provided information by the Environment Agency's Fluvial Design Guide, Chapter 9

Both temporary and demountable defences require a considerable amount of preplanning to ensure that they can provide an effective defence. It is essential that the operational resources, storage facilities and the logistics of deployment are fully appreciated by anyone planning to rely on these types of defence.

Temporary flood barriers

There are many forms of temporary flood barrier, ranging from sandbags to the so-called pallet barrier. These are suitable for deployment in response to a developing flood in situations where there are no permanent defences or where the existing defences are not high enough.

Sandbags can be used to provide a degree of protection at the entrances to individual properties. They have also been used successfully to raise the crest level of significant lengths of flood embankment. However, sandbags do not provide a watertight defence and are practical only up to a height of about 0.3m, perhaps 0.5m in ideal circumstances. They require considerable effort to deploy and often prove ineffective.

The pallet barrier is a more sophisticated system which is deployable over a length of several hundred metres. It consists of a lightweight structural system which supports an impermeable membrane. The system relies on a reasonably firm and level foundation. The effective use of such sys-tems also depends on the ability to mobilise them fairly quickly in response to a growing threat of flooding. Storage of the necessary equipment reasonably close to the site is therefore essential, otherwise there is a risk that the defence will not be delivered to site and erected in time to prevent flooding (see also the guidance below on demountable defences in this regard).

Whereas temporary barriers may seem to offer a viable solution in situations where there is sufficient time to mobilise and erect them, such systems have other potential disadvantages. It is essential to ensure that no significant drains or other flow pathways are present that would compromise the effectiveness of the defence. There are also likely to be issues with parked cars and road closures that may delay the deployment of the defence to the point where deployment is too late.

Temporary barriers therefore require a considerable amount of preplanning to ensure that they can provide an effective defence. For any type of temporary defence, it is essential that the operational resources (labour, plant and equipment), storage facilities (access to and from, security, proximity to point of deployment), and the logistics of deployment are fully explored before the commitment to rely upon this approach is made.

Demountable flood defences

Demountable flood defences are used where a permanent defence is unacceptable, usually because of the visual intrusion and loss of amenity that a permanent defence would entail. These are relatively new to the UK, but have recently been successfully installed and operated in Shrewsbury and Bewdley on the River Severn, and in parts of north Wales.

Time is the key factor concerning the adoption of demountable defences. There must be sufficient advance warning of a flood to allow the defence to be deployed. In addition, the advance warning must be reasonably reliable so as to avoid excessive precautionary deployment of the defences. They are therefore suitable on the middle and lower reaches of the River Severn, for example, where flood conditions can be predicted days in advance, then confirmed with plenty of time to mobilise the erection team. Demountable defences may make use of standard panels, but they often have to be custom-designed to suit a particular location. They rely on built-in foundations for stability and ease of erection.

The components of the demountable defence must be stored relatively near to the site to reduce the risk of delays once the decision to mobilise has been made. A skilled erection team is required to ensure that the defence can be safely and securely erected in the limited time available. For practical reasons, the length of a demountable defence is unlikely to exceed a few hundred metres.

Whereas demountable defences may seem to offer the ideal solution where visual impact is a key factor, this form of defence tends to be expensive and there will always be a risk that the defence elements are not deployed in time to avert flooding. Theft of defence units, damage to built-in parts and delays in transporting the units to site can all conspire to make deployment problematic.

In July 2007, the delivery of the components of a demountable defence at Upton-on-Severn was delayed due to the severe disruption to the transport infrastructure caused by surface water flooding. The defence was not deployed in time and there was considerable flood damage as a result. In fact, had these demountable defences been deployed, they would have been overtopped due to the severity of the flood, but this example illustrates just how important it is to make sure that these defences can be successfully deployed in a flood event.

Further Readings

Ogunyoye, F and van Heereveld, M (2002). Temporary and demountable flood protec…

Scale

Measure category

Flood embankments and Floodwalls

giacomo.cazzola — Thu, 08 Sep 2016 13:37:11 +0000

Flood embankments and Floodwalls giacomo.cazzola Thu, 09/08/2016 - 15:37

Flash floods

Water flow regulation

Hold the line

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.

Based on "C E Rickard (2009): 9 Floodwalls and flood embankments 29p. In: UK Environmental Agency (2009): Fluvial Design Guide (Contains public sector information licensed under the Open Government Licence v3.0.)"

Flood embankments

Flood embankments are earthfill structures designed to contain high river levels. They are commonly grass-covered, but may need additional protection against erosion by swiftly flowing water, waves or overtopping. Protection may take many forms, but options include: stone riprap; gabions and gabion mattresses; open-stone asphalt; concrete bagwork; concrete blockwork (which can either be individual blocks or linked to form a mattress); various products that may be categorised as bioengineering such as coir rolls, faggots and fascine mattresses. Geogrids and geotextiles can also be used to reinforce grass on flood embankments.

The basic form of a flood embankment is trapezoidal in cross section, with a horizontal crest and sloping inner and outer faces.

The width of the crest is normally determined by asset management requirements, with widths of 2m to 5m being the normal range. In the absence of more specific guidance, designers are advised to adopt a crest width which is two metres wider than the maximum width of plant that will be used on the crest (allowing one metre safety margin on each side).

The slopes of the inner and outer faces are a function of:

the strength characteristics of the earthfill material used;
the type of maintenance equipment used (for grass cutting, for example);
any landscaping requirements.

Normally the embankment side slopes are between 1:2 (vertical to horizontal) and 1:3. Steeper slopes are very difficult to maintain (grass cutting), while flatter slopes tend to add unnecessarily to the footprint of the embankment and the quantity of fill material required.

An embankment with relatively steep face slopes has a smaller footprint and lower earthfill require-ment than one with more gentle slopes; it may therefore cost less and have a lower environmental impact. Steeper slopes can be achieved by using earthfill with a higher clay content or by a range of soil strengthening techniques, but designers must always take into account the asset management needs and ensure that these can be carried out safely (for example, avoiding the risk of maintenance plant overturning on a steep slope). The designer must be certain that the profile of the embankment selected meets all the service requirements and, in particular, is stable throughout the full range of loading conditions.

Embankments are normally set back from the edge of the river to:

allow for some flood storage on the floodplain;
reduce the risk of undermining caused by riverbank erosion.

Set-back embankments are also less prone to erosion of the riverward face due to high velocity flow, but may be more prone to wave damage.

Flood embankments can be constructed from a variety of earth materials. Wherever possible, locally won material should be used, to reduce costs and lessen the environmental impact. The strength of the material used to construct the embankment is increased by compaction, which is a fundamental part of the construction process. The required strength is achieved by constructing the embankment in layers and compacting each layer using mechanical plant appropriate to the type of soil. It may be necessary to add water to each layer to improve the degree of compaction required; this depends on the nature of the soil and its moisture content. The advice of a geotechnical engineer should be sought regarding the appropriate layer thickness and the type of compaction plant required.

Soils with high clay content are best avoided because these crack when they dry out, and such cracks can extend a metre or more into the bank, compromising its function as a flood defence. Soils with a high sand or gravel content can be used, but may have to incorporate some form of cutoff to reduce seepage in flood conditions. Granular soils are less resistant to erosion than cohesive soils once the topsoil layer has been eroded.

Because of the shortage of suitable fill and the adverse environmental consequences of importing large quantities of fill from afar, various alternatives to conventional fill material have been explored. These include the use of recycled tyres compressed into bales to form a central core to a flood embankment. Options such as this need careful investigation before being adopted, with particular emphasis being given to long term durability and stability, environmental risks (such as contamination) and the overall environmental impact.

It is normal to strip topsoil from the foundation of an embankment before construction starts. This helps to key the embankment to its foundation and reduces settlement. It also provides a source of topsoil to encase the embankment and allow the establishment of a suitable grass cover.

Where the foundation soils are weak (for example, a layer of peat), the options are:

remove the weak layer (if it is near the surface and relatively thin);
strengthen the foundation (potentially an expensive option);
accept and allow for the resulting long-term settlement;
pre-load the foundation to accelerate settlement.

If the foundation is highly permeable (for example, a thick layer of gravel), it may be necessary to take steps to cut off the seepage path through the foundation.

Embankment foundations should always be checked for the presence of buried (agricultural) land drains prior to construction, as any that are left in place could result in excessive seepage and even embankment failure.

Other services may also be present along the route of the flood embankment, and these may need to be diverted or protected to avoid damage. The cost of diverting a gas or water main can be significant, but is normally much less than the costs from accidental damage during construction of the embankment!

Embankments in rural settings are often accessible by livestock and agricultural machinery. Both can cause significant damage, degrading the bank crest where they regularly congregate or cross the defence. Fencing can be used to control livestock movement, and pathways and machine access routes can be surfaced to reduce the likelihood and amount of damage. Cattle can be prevented from grazing flood embankments by providing two strands of barbed wire at the top of fence posts. The height of the lower strand can be high enough to allow sheep to pass under, as sheep do not cause damage to the embankment surface. Stock-proof fencing may be required at field boundaries. Gates or stiles may be required to maintain pedestrian access.

If a high level of burrowing damage is expected, it may be appropriate to incorporate a deterrent (such as wire netting) into the surfaces of the embankment.

Cracks in embankments can create seepage paths. Cracking occurs in clay soils during dry conditions and is best avoided by not using highly plastic clay soils for fill in the top metre of the crest.

Seepage can also occur where structures pass through the embankment (for example, a drainage culvert). The soil–structure interface requires careful attention during construction to minimise this risk, most notably by ensuring good compaction of the embankment fill around the structure. The likelihood of seepage can also be reduced by lengthening the seepage path (for example, by constructing a concrete collar round a pipe passing through the embankment)

Floodwalls

There are two basic types of floodwall:

those that also form part of the river frontage, such as a wharf, retaining wall, or quay;
those that are remote from the river, generally with the sole purpose of providing a flood defence.

Defences that form part of the river frontage usually have deep foundations and considerable overall height. Often such walls have been in existence for many years and their flood defence function has increased with time, with progressive heightening of the crest level. Such defences need careful investigation if they are to be upgraded or refurbished to provide an acceptable service life.

The form of construction of such walls includes brick, masonry, timber, sheetpiling and concrete.

The main factors to consider include:

the type, condition and stability of any existing foundations;
the presence of historic wall elements that might make driving of new sheetpiles very difficult (old timber piles that have rotted away often leave embedded parts in surprisingly good condition – these can present significant obstructions to the driving of new piles);
there may be a requirement to conserve historic elements of a wall;
the need for tie rods or ground anchors to restrain the wall against overturning (commonly used with steel sheetpile walls);
the need for access ways in the defence to allow the continuation of business and leisure activities on the river frontage;
traffic loading surcharge on the landward side (these can be particularly onerous at an operating wharf or quayside);
additional loadings on the wall from mooring or boat impact;
the need to accommodate diurnal variation in river level for tidal rivers (which may result in daily changes in the hydrostatic pressure direction on the wall).

Should the existing river frontage not be suitable for upgrading or rehabilitation (having reached the end of its service life), the option of setting the floodwall back from the frontage should be considered. This has implications for the flood defence of the land between the river and the floodwall, but may be the only acceptable option if the flood defence is to remain independent of the frontage and thereby not dependent on its stability. Such a situation is likely to arise when the party responsible for constructing and maintaining the flood defence does not have (and does not want to take on) any responsibility for the existing river frontage structures.

For defences remote from the river, construction tends to be more straightforward. Concrete (both precast and insitu) is the most common form of construction, often with some form of cladding or decorative finish. Brick and masonry can be used, but these either have to be massive structures (unless very low in height) or be reinforced with steel bars. Low brick walls can be formed by constructing a tied cavity wall on a concrete foundation, with reinforcing bars extending from the foundation up the cavity. The cavity can then be filled with concrete, during which the brick skins may need external support while the concrete in the cavity hardens.

Where a cutoff is required, a sheetpiling wall offers the advantage of providing both the cutoff and the wall – though it is normal to clad the wall with brick or masonry to improve its appearance. Where space permits, one side of a sheetpile wall can be given a ‘half-bank’, so that it appears to be a flood embankment from that side.

Standard precast wall concrete units offer the advantage of speed of construction, but may lead to wastage if the ground level along the wall alignment is very variable, requiring the wall height to vary. (The advantage of using precast units is reduced if many different sizes are needed or if the largest size required is used throughout.) Cast insitu walling is more often used where there are frequent changes of direction or wall height.

Where a floodwall passes through private land, there may be a need for an easement to ensure the right of access for inspection and maintenance is provided for ever.

Scale

Regional

Measure category

Rivers dredging

giacomo.cazzola — Thu, 08 Sep 2016 13:17:52 +0000

Rivers dredging giacomo.cazzola Thu, 09/08/2016 - 15:17

Limited intervention

The beneficial re-use of dredged material

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.

Based on "A T Pepper, C E Rickard (2009): 8 Works in the river channel. 36p. In: UK Environmental Agency (2009): Fluvial Design Guide (Contains public sector information licensed under the Open Government Licence v3.0.)"

Dredging is an expensive operation and can have severe environmental drawbacks. The expense is not only in the dredging operation itself but also the disposal of the dredged material, which may be contaminated and require disposal to a licensed landfill, with associated transportation costs. Dredging should therefore be avoided wherever possible, especially since it is almost never a ‘one off’ operation.

Environmental damage can be reduced by carrying out the dredging in the appropriate season, for example to avoid polluting fish spawning grounds with fine sediment disturbed by the dredging process. Avoidance of the summer season when boating and other river-based activities are at their peak is also advisable, but this may leave a narrow window for the dredging operations when other restrictions are taken into account.

The environmental impacts can also be minimised by choosing the right plant and equipment for the dredging. Mechanical removal of material from the bed (for example, using a dragline or a grab) is likely to create the most disturbance and hence sediment pollution, although measures can be taken to reduce this impact.

The sediment derived from the dredging can be re-used for DRR measures. How this can be achieved, can be read here.

Further Readings

Scale

Measure category