Deal with the effects

Dry proofing - sealing and shielding

giacomo.cazzola — Tue, 06 Sep 2016 08:23:16 +0000

Dry proofing - sealing and shielding giacomo.cazzola Tue, 09/06/2016 - 10:23

Riverine or slow rise floods

Flash floods

Estuarine floods

Coastal floods or storm surges

Urban floods

Reduction

Deal with the effects

Grey infrastructure

Dryproofing makes a building watertight and substantially impermeable to floodwaters (FEMA, 1993). Compared to wetproofing, dryproofing requires a more reinforced building structure to withstand floodwater pressures and impact forces caused by debris. Other important factors to be considered in dryproofing are watertight closures for doors and windows, prevention of floodwater seepage through walls, and check valves to prevent reverse flows from sewage.

Based on kindly provided information on the Flood Management Tools Series by the Associated Programme on Flood Management

Before selecting dryproofing as a viable floodplain management tool, numerous factors must be considered, such as flood warning time, purpose of building usages, mode of building entry and exit, flood depths, floodwater velocities, floating debris impact, flood frequency, etc. The flood proof function must work sufficiently for design flood level and additional freeboard is recommended because flood depth estimation includes a certain error and may be influenced by future development in the basin.

Sufficient warning time, which is calculated by the rate of floodwater rise and the existing flood warning system, is necessary for evacuation from a flood prone building, for installation of removable flood shields or gates, and for operation of sump pumps and check valves. If the warning time is limited, for example the structure is located in a flash flood area, flood proofed buildings should not be considered as the necessary operations to make it flood proof will require too much time. FEMA suggests flood velocity of 5 ft/s (1.5 m/s) and flood depth of 3 feet (90 cm) as thresholds for adopting dryproofing. If the flood exceeds these limits, the cost of dryproofing may become too significant and the dryproofing method is therefore not feasible. Any areas susceptible to severe debris flow, such as mountainous regions or areas facing ice flow in winter, are not suitable for flood proofed buildings in a cost.effective manner.

The building structure must be able to resist four types of flood.related forces: (1) hydrostatic flood force that freestanding water exerts on a submerged object; (2) buoyancy force that a building receives from surrounding floodwaters; (3) hydrodynamic force that vertical surfaces receive from moving floodwaters; and (4) debris impact force to withstand the flood.borne debris strikes on the side of building. FEMA provides an estimation formula for each force (Appendix 2). For more detailed standards of dryproofing structure design, FEMA has a comprehensive guidance and case study report “Engineering Principles and Practices for Retrofitting Flood.Prone Residential Structures” (FEMA, 2012).

Flood Shields for Openings

Doors, windows and air vents of buildings are potential flow paths where flood water runs into properties (DCLG, 2007). Raising the threshold of doors as high as possible without disturbing accessibility is a primary prevention measure. Sealed polyvinyl chloride (PVC) framed doors are a more preferable option than wooden doors and the doors should be properly fitted to their frames. Windows are also vulnerable to flood water and preventive measures of fitting and sealing similar to those for doors should be taken. The windows should adequately resist the pressure of flood water and prevent damage that could be caused by debris flows. Regarding ventilation vents, special designs of air vents that prevent water from entering into the premises are available on the market.

Temporary flood protection system

A temporary and removable flood protection system is provided in locations where permanent flood defences would not be suitable because they are not technically, economically or environmentally feasible (DEFRA, 2011). The temporary system includes a pre-installed system that requires operation; the system may be installed in a pre.constructed foundation, or it may also be a system where the whole of it is movable and needs to be installed. DEFRA defines the first two systems as “demountable systems” and the third one as a “temporary system” . These systems are further classified by their different structures, such as earth filled containers, air and water filled tubes, and panel type flood barriers.

In contrast to a permanent flood protection system, a temporary system brings an additional risk of operational failure. Taking this fact into consideration, a permanent system should be given priority if it is feasible and locally acceptable. In the event of a temporary system being adopted, it should be ensured that the movable parts of the system are at a minimum and that the reliability of all the operational processes including mobilization, installation and closure are at a maximum. If the temporary system requires significant preparation time, it is suitable for location at the downstream of a large river basin.

A temporary flood protection system can allow a dual function by ensuring effective flood control performance without obstructing the ordinary use of the building, for example access through a floodwall, or parking lot turning into a flood protection site. A temporary system also adds additional safety to a permanent system, which is often the case in critical disaster situations. There are several factors affecting the risk of operational failure, such as sufficient lead.in time, reliability of flood forecasting and warning, system maintenance, and training of operators. Because the flood warning system usually triggers the operational process of the temporary system, technical and human operational reliability is a pre-requisite for the temporary system. Regular training and emergency exercises together with flood operation manuals increase the reliability of the total system. Different temporary systems need different levels of installation skills and preparation time. Site.specific conditions, such as the location of the stockyard of the system parts, transportation means, and available resources of personnel and equipment, also affect the selection of an appropriate temporary system. Detailed advantages and disadvantages of different temporary systems and commercially available products are explained in “Temporary and Demountable Flood Defences” (DEFRA, 2011).

FEMA (Federal Emergency Management Agency), 1993: Non-Residential Floodproofing - Requirements and Certification for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program. FIA.TB.3. www.fema.gov/library/viewRecord.do?id=1716

FEMA (Federal Emergency Management Agency), 2012: Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures (Third Edition). https://www.fema.gov/media-library-data/20130726-1506-20490-2593/fema259_complete_rev.pdf

DCLG (Department for Communities and Local Government), 2007: Improving the Flood Performance of New Buildings – Flood Resilient Construction. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/7730/flood_performance.pdf

DEFRA (Department for Environment, Food and Rural Affairs ), 2011: Temporary and Demountable Flood Protection Guide. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/290837/scho0711buak-e-e.pdf

Scale

Individual - private

Measure category

Mitigation

Wet proofing - Sealable buildings

giacomo.cazzola — Wed, 31 Aug 2016 12:38:10 +0000

Wet proofing - Sealable buildings giacomo.cazzola Wed, 08/31/2016 - 14:38

Riverine or slow rise floods

Flash floods

Estuarine floods

Coastal floods or storm surges

Urban floods

Reduction

Deal with the effects

Grey infrastructure

Wetproofing (or wet floodproofing) is different from dryproofing in that it allows flood water to enter a structure, though both floodproofing methods have the same purpose, that of preventing damage to the structure and its contents and creating no additional threats to public safety (FEMA, 1993).

Based on kindly provided information on the Flood Management Tools Series by the Associated Programme on Flood Management

Equalizing water levels on the inside and outside of a building by wetproofing can result in some advantages for the building structure. Firstly, because the difference in interior and exterior water levels causes hydrostatic pressure on the building walls, equalizing water levels by keeping the change at the same rate minimizes the hydrostatic pressure and thus the building does not require such a strong structure to withstand such pressure. Secondly, inside water reduces the buoyancy effect of hydrostatic uplift forces. Although a wetproofed building is relatively less affected by hydrostatic and hydrodynamic forces, the structure must be adequately anchored to prevent floatation, collapse, or lateral movement. Without engaging in major structural reform, wetproofing is often a more cost effective measure for buildings.

On the other hand, disadvantages of wetproofing are obviously caused by water entering the building. To prevent damage to the contents of a building, mechanical and utility facilities (such as electrical, heating, ventilation, plumbing, and air conditioning equipment) must be elevated above the expected flood level or must be protected from flood water entering or accumulating within the various components. Empty liquid containers, including the ones buried underground, should withstand a buoyant force by anchoring or even filling them with potable water before flooding (of course, after the flood quality control should be established and implemented before using the water stored in the tank). Because windows are especially vulnerable to flood waters and debris, protective screens, reinforced glass and impact.resistant plastic are recommended solutions.

Before adopting the wetproofing method, the site situation should be carefully considered. Wetproofing is not appropriate if the site experiences rapidly rising flood water, high.velocity flood waters, and a short flood warning time. In this case, elevation or relocation of buildings are more preferable solutions. If a wetproofed facility requires some preparation time for minimizing flood damage, for example shifting or elevating equipment or content, sufficient warning time is necessary. If the facility needs to be accessed during flooding, safe access routes should be secured for either escaping from, or gaining access to, the site.

Because most of the existing facilities do not expect to come into contact with water and often use permeable construction materials, retrofitting wetproofing techniques by applying flood resistant materials are necessary. The materials must be resistant to flood forces, deterioration caused by repeated inundation, and excessive moisture and humidity during and after flooding. Because flood water contains silt, chemicals, and organic materials, which can be hazardous to the structure and the residents, the structure and the materials need to be easily cleaned without leaving any contaminants. Concrete, hard brick, plastic, metal, and pressure.treated wood are possibly suitable materials for covering walls and floors. Cleaning up after a flood includes washing and disinfecting walls, floors, and other surfaces. Because flood.induced mould and contaminants are hazardous to human health, wetproofing is not suitable for living spaces (FEMA, 2009). After the cleaning process, the drying out process can take up to six weeks to remedy any structural damage and health problems.

Another category for which adopting wetproofing could be considered includes structures located near water and functionally dependent on water uses, such as docking, seafood processing, port facilities, and ship repair facilities. Moreover wetproofing may be suitable for agricultural structures used for production, harvesting, storage and drying, provided that agricultural commodities and livestock are raised and kept dryproof.

Wetproofed structures must meet the required technical standards, conducting site-specific evaluation by technical experts or designated government offices, if necessary. In addition to the standards, all kinds of local or national regulations, building codes, etc. should be met. It should be noted that some local regulations may exceed national regulations. Combining wetproofing with dryproofing and elevation may achieve optimal protection for the site. Before implementation, an economical assessment and evaluation is required to understand if the cost of business interruption and cleanup activities may make wetproofing less feasible in comparison with dryproofing.

Adaptive management

nst — Tue, 14 Jun 2016 14:50:07 +0000

Adaptive management nst Tue, 06/14/2016 - 16:50

Riverine or slow rise floods

Estuarine floods

Coastal floods or storm surges

Erosion

Avoidance

Deal with the effects

Ecosystem based approach

Highly dynamic coastal systems (like sandy beaches, dunes or estuaries) might be best managed by not interfering with the natural processes, but instead accepting that change will occur and adapting backshore management accordingly. Key in this approach is a proper monitoring of the processes to analyze and evaluate the changes (for examples at eroding cliffs or dunes). With a proper planning horizon, these changes can be anticipated and with enough room for the environment to involve this can be a very cost-extensive approach.

Based on kindly provided information by the Scottish Natural Heritage

Technical feasibility

Adaptive management should be considered at all sites before considering any of the other options of hard engineering coastal defence measures. In some cases this can mean loss of land or other values, so an assessment of these impacts has to be carefully undertaken with the integration of relevant stakeholders.

In contrast to managed realignment, this measure is not a planned retreat (e.g. with opening of dykes or removal of groynes). Instead it is the allowance of natural processes that could lead to relocation of the coastline but does not necessarily have to.

If management of marine erosion is being considered it is assumed that assets of value are being threatened. These assets may be natural, such as a rare habitat or a particularly interesting geomorphological feature. In general erosion of such features would be considered part of their natural evolution and therefore preferable to management interference. More often the assets will have socio-economic importance, ranging from amenity access to a beach up to an industrial complex or power station. The shoreline manager must start by considering the value of the assets that may be at risk, then try to establish an understanding of the likely future evolution of the beach/dune system. Finally the manager must determine whether it is better to lose/move the assets or attempt to prevent or reduce the erosion.

Consideration from Italy: Retreat is expensive - staying too!

Political & social feasibility

Monitoring, consultation and education are at the heart of adaptive management. The shoreline should be continuously assessed using data collected from site, combined with any available historic or published data. The monitoring will allow the management policy to be reviewed from time to time. Impacts of the policy on recreation, land use and habitats should also be monitored.

Consultation is required to assess the values associated with the backshore, and to develop a consensus view on how to deal with the assets. This process is firmly linked with education, requiring the manager to set out the background issues in a language that can be readily appreciated by those who are affected.

Those responsible for the management of eroding dunes and cliffs should be aware of the potential danger to the public of a collapsing dune or cliff face. Dangers exist both from falling down the face and from being buried at the base. Warning signs set up along the crest and at public access points should be the minimum response to these dangers.

Cost of implementation & maintenance

The value of the backshore may be assessed in economic terms, based on the present replacement cost of buildings, infrastructure or land. The assessment should also consider the wider values such as potential loss of jobs, transport routes, rare habitats, recreation or cultural heritage (i.e. archaeological sites). This assessment therefore considers costs and benefits (SET LINK).

Costs associated with adaptive management are site specific and cannot be generalised. Accepting the gradual loss of a site valued as an undeveloped public recreation area may incur no actual cost at all apart from monitoring and minor works to delay erosion or encourage. At the other end of the scale the demolition and replacement of threatened shoreline buildings or recreational facilities may be very cost intensive.

Ecological feasibility

Adaptive management minimises interference with the natural processes and ecosystem of an evolving dune system. The approach allows for the sustainable, long term management of the shore, with no environmentally disruptive engineered schemes.

Key lessons learnt

Adaptive management can result in the controlled loss of backshore assets and the continued evolution of dune habitat and land form. This approach can be highly emotive, with local interest groups protesting vigorously and demanding that more positive actions be taken. However, it must be accepted that both erosion and accretion are natural elements of coastal evolution, and that maintenance of natural evolution is, wherever possible, preferable to costly and environmentally disruptive intervention.

Scale

Local

Regional

Measure category

Prevention