Coastal flood Hazard level: High ?

In the area you have selected (Dhaka) coastal flood hazard is classified as high according to the information that is currently available. This means that potentially-damaging waves are expected to flood the coast at least once in the next 10 years. Based on this information, the impact of coastal flood must be considered in different phases of the project for any activities located near the coast. Project planning decisions, project design, and construction methods must take into account the level of coastal flood hazard. Further detailed information should be obtained to adequately account for the level of hazard.

Climate change impact: According to the IPCC (2013), there is high confidence that extremes in sea level will increase with mean sea level rise yet there is low confidence in region-specific projections in storm surges. Projects in low-lying coastal areas such as deltas, or in island states should be designed to be robust to projected increases in global sea level.

Recommendations

• INTERACTING HAZARDS: Project planning, design, and construction practices should account for coastal flood and storm surge from cyclones and other weather events occurring in your project area. More information
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  Context - The most common, and often very costly, damage from coastal flooding is to the foundation, basement, and lower stories of a property. In the design phase of your project, carefully consider the placement of permanent building infrastructure including electrical, mechanical (e.g., HVAC), and other services and utilities. When a building is flooded at ground level and the foundation is breached, damage is exacerbated. If the project involves significant storage of valuable assets (e.g., warehouse, production facility), consider the impact on operations and potential financial loss to those building contents in the event of a coastal flood.

  • Coastal flood risks are defined by water levels and water velocity. The levels determine how much of the building from the ground up is exposed to potential damage. Water velocity is often discounted or entirely ignored although it is often responsible for as much or more damage than water contact alone. As with wind, rapidly moving flood waters can carry large and heavy debris that upon impact can cause direct physical damage. Soil scour within fast moving water can penetrate the building envelope and lead to expensive clean up costs. Be mindful of these risks by evaluating surrounding land use and potential land development in the vicinity of your project area.

  • An intense cyclone or other weather event can bring torrential rains and have embedded severe thunderstorms that are accompanied by strong winds from tornadoes. When combined with coastal storm surges, the impacts can be catastrophic. Buildings damaged by coastal flooding often suffer wind damage as well. Water driven by hurricane-force winds can enter a building through otherwise sealed openings, and rain entering through a damaged roof can compromise the inside of the building and in some cases expose the building to dangerous water-borne pathogens (e.g., mold). In your planning process, think holistically about all sources of damage especially those related to water penetration of the building envelope.

  • The risks of water damage and the health dangers of mold go hand-in-hand. After a coastal flood event, its important to have a post-disaster response plan that requires rapid inspection and response to prevent further damage and complications. Flood waters carry contaminants such as oil, pesticides, bacteria, and heavy metals. Keep in mind certain finish materials (e.g., carpeting) tend to retain moisture and develop mold days or weeks after a flood event ends, posing a serious health hazard if the building is reoccupied prematurely. Beyond your project’s base requirements, consider choice of building materials and finishes from a risk mitigation perspective.

  • Note that coastal flooding is not the only cause of direct physical damages from tropical cyclones and other weather events. For example, wind-borne debris can enhances damage to a structure already compromised by flooding at the ground level. Damage can be further induced by heavy rainfall and subsequent inland flooding especially after the roof and/or windows or other openings are compromised by wind-borne debris. Considering all weather hazards in the design and planning stages results in efficient risk management for your project.

  Mitigation - Throughout the project from design to construction, consider all available mitigation strategies to reduce your coastal flood risk from cyclones and other weather events. Balance the cost of mitigation features with the long-term savings via reduced damage and lower cost of repair and replacement.

  • Further detailed information should be obtained to account for the risk from other hazards related to cyclones and other weather events. Be sure to review the ThinkHazard! assessment for related hazards in this region: cyclone wind, river flood, and landslide. Keep in mind wind forces can stress structural components including the foundation that in turn subject a building to an elevated risk of flooding.

  • In terms of replacement cost, basements, lower stories, and foundations can experience significant damage and as such are as important as the materials used for roofs, walls and building connections. Foundation design strongly influences a building’s resilience to coastal flooding. Properly sealed and infilled foundations tend to be the most resilient.

  • Investigate national building codes for coastal flooding in your project area. Also determine from your local authorities whether local building codes override national codes, in particular along the coast where the combination of coastal surges and strong winds from cyclones are most risky. Be responsive to national and local building code requirements for coastal flooding hazards as following these codes may considerably reduce future losses.

  • Start by consulting with widely accepted building code organizations such as the ICC (International Code Council) to access commercial and residential code (ICC/IRC) standards pertaining to your project.
  • Next, determine if your region has adopted international codes or has modified them locally. Consult your jurisdictional planning division for the most up-to-date information on building codes. Be mindful of recent code changes as they are often developed in response to recent adverse natural events that have caused loss to similar projects.
  • If national structural design guidelines do not exist, safe design practices to mitigate coastal flooding should be obtained from other countries with a similar level of risk or from international guidelines.
  • Contact other national or local organizations that may have supplemental information on coastal flooding (e.g., meteorological agency, national research council, engineering associations, etc.).

  • Investigate local council and planning commission meeting minutes as they often contain useful information about best practices and emerging mitigation strategies.

  • As a part of comprehensive risk management, consult the International Property Maintenance Code (IPMC) to assure your project has long-term resilience to flood damage. Be sure to plan for proper maintenance post-construction.

  • In high-risk areas along the immediate coastline, carefully design around your BFE (Base Flood Elevation). A first floor raised just one foot (0.3 meters) above the BFE can result in a 50% reduction in overall flood risk. Also consider extended foundation walls and other means of reducing the risk to the main building structure and its contents.

  • Carefully consider foundation construction in the design phase and select high quality materials. The most important construction measures to minimize flood damage surround the foundation and its reinforcement as well as connections to the main building structure and the planned use of basement and lower stories.

  • Distinguish carefully between coastal flooding and riverine (inland) flooding. For example, a common structural mitigation for river floods is in the use of reinforced concrete footings and attached piers. However, piers are not suitable as a defense against coastal floods because they cannot withstand the pressure forces exerted by coastal storm surge. Most effective coastal flood mitigation strategies account for the predominant source and direction of the water flow.

  • In very high-risk areas, consider designing for a moveable structure. When practical, temporarily relocating a building provides the greatest mitigation against coastal flood risks. In such cases, consult with your local jurisdiction for structural and safety requirements around replacing the building structure to its original location.

  • Be aware of and plan for the after-effects of a coastal flood event. Over time, flooding can cause substantial beach erosion in the absence of physical damage to a building lying along that beach. In time, the erosion can lead to a substantial increase in latent (hidden) risk. Track your beach erosion rate carefully within the natural course of your project’s maintenance and upkeep schedule. In some cases, a building may be subject to imminent collapse even without a precipitating flood event.

  • As a part of a long-term maintenance strategy, identify and remove small trees and branches from larger ones that could detach during a flood event and pose debris risk to the building. Identify and repair loose or damaged building components such as sheathing, soffit and fascia, shingles and roofing, brickwork, and jutting building features such as chimneys as all of these become potential debris in flood (as well as projectiles in wind).

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• EMERGENCY RESPONSE PLANS: Identify the regional and national government’s emergency response policy and protocols to coastal flooding in your project area and incorporate as necessary. More information
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  • During the design and construction phases, set aside ample time to thoroughly review the emergency response procedures laid out by your local and national governments and, if necessary, make changes to project design and implementation to account for these procedures. These procedures will have already taken into account the significant hazards inherent to your region, including coastal flood hazards and other related risks to your project.

  • Adopt your own emergency response procedure leveraging response plans already in place regionally. Your plans should include specific conditions that will activate the plan, a clear chain of command and orders of responsibility, a list of specific emergency functions and who will perform each of them, evacuation procedures, including evacuation routes and emergency exists, and procedures to account for personnel, customers, and visitors as appropriate. Be sure to secure and maintain proper emergency equipment for personnel including medical kits.

  • Train personnel on emergency response procedures. Prepare for real-time response with unannounced drills and conduct post-mortems to improve personnel preparedness. If your project includes a safe room or outpost, clearly advertise its location and include access and supplies as a part of your overall emergency response plan.

  • Don’t store emergency equipment in the basement or lower stories of the building. Flooding may inundate the lower levels and render generators and other critical assets inoperable.

  • Remain aware of your government meteorological organization’s watch and warning protocols. When a warning is issued, be aware of the meaning of such a warning and be prepared to clearly communicate its implications to your personnel and visitors. Clearly define the circumstances that would lead to retreat to a safe room, voluntary and mandatory evacuation procedures, operations shutdown, etc.

  • Develop a task checklist for your emergency response plan, and maintain that list at least once per year. The checklist can be customized to each stage of your project or draw attention to tasks more critical in a particular stage (e.g., construction sites will have more potential outdoor airborne debris). A sample checklist to protect against tropical coastal flooding is shown below.

  • Clean floor drains, catch basins, and pumps to ensure proper drainage.

  • If practical, move outdoor storage and unanchored property indoors.
  • Anchor and fill tanks (unless below ground) to capacity with product or water to minimize tipping hazard.
  • Move drums and other portable tanks containing flammables to a properly protected and secure area indoors.
  • Maintain an inventory of flammables and caustic or dangerous materials on site.
  • Secure outdoor cranes in accordance with manufacturer’s instructions.
  • Fill emergency generator fuel tanks.
  • Inspect all fire protection equipment to be sure they’re operational.
  • Move important records and documents to a secure and protected area. If there’s time, duplicate records and move offsite.
  • Shut down any production processes safely and in a timely fashion. Prepare personnel in advance of the shutdown.
  • Shut off supply lines to flammable liquids, combustible liquids and gas at their source.
  • Shut off electrical power at the main building disconnect before the flooding occurs.

  • Evacuate personnel and, if safe for emergency response teams to remain, ensure that team has the following:

    • Nonperishable food
    • Two-way radios with spare batteries
    • Ample supply of stored drinking water
    • Flashlights and batteries
    • First-aid supplies
    • Vehicles with full gas tanks
    • Gloves, boots, and hard hats
    • Supply of dry clothing

  • After construction is complete, remain mindful of emergency response procedures. If they change with regard to the hazards of coastal flooding, consider increasing your resilience via improved building mitigation and/or additional insurance coverage.

  • It’s imperative to plan in advance for all aspects of a catastrophic weather event. In major coastal flooding events flood debris is inevitable, especially in built up areas, but often unplanned for. In addition to preparing for exacerbated damage from debris, and the associated injuries and health hazards, you should plan for debris clean up, especially if it is expected to interfere with operations of the residence or business. Keep in mind debris comes from other areas, buildings, and surfaces, thus be wary of surrounding structures especially if hazards (e.g., explosive material) may be contained in nearby structures or adjoining grounds. Where coastal flooding is a product of cyclone winds, the most common debris include damaged building components and building contents, sediments, green and bacterial waste, and personal property. Other forms of debris are associated with the strong winds and debris from coastal surges can occur many miles from the coast. Debris collection and removal can be extremely costly, and recent experience has shown debris removal is often more costly than direct physical damage to the building itself.

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• TECHNICAL EXPERTISE: Consult with an expert familiar with coastal flooding risk that has experience with natural hazards and/or construction practices in your local area. Such consulting professionals include structural engineers, civil engineers, and atmospheric scientists. Incorporate local and subject-matter expertise in the design, construction, and maintenance phases of your project. More information
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  • To learn more about the risks, engage with qualified meteorological and engineering experts with the goals of:
  • Understanding the frequency and intensity of coastal flooding and other natural risks to the project
  • Determining how local site conditions may increase or decrease such risks to the project
  • Learning about recent and/or nearby events that can provide real-life context to the risks and impacts
  • Supervising design, construction and maintenance from a flooding perspective
  • Understanding and adapting proper mitigation strategies based on the current state-of-science
  • Conducting cost/benefit studies to evaluate and prioritize mitigation, insurance, and resilience

  • Interviewing local staff and residents having local experience with any aspect of risks to your project

  • Experts can provide significant value to your project since the risk is significant. During the design and construction plan review phases, structural engineers will review the latest available literature and industry data to confirm the extent that your project is exposed to the dangers of coastal flooding, and propose mitigation measures to protect your assets. Experts can also review recent historical events that have affected your region and how nearby buildings have performed under damaging flood conditions. With this prior knowledge, your project managers can evaluate mitigation and risk transfer options well before construction begins and plan accordingly.

  • After construction is complete, experts can evaluate the scientific literature published since construction began to determine if the risk is even higher than previously suspected and also suggest additional steps to increase resilience. Regardless of whether the risk has changed, experts can propose long-term mitigation strategies, methods of disaster preparedness and response, and the cost/benefit of insurance coverage given the expected risk levels. In the event flood risk has increased, the expense of hiring an expert will be justified by drawing attention to potential future losses and accounting for those risks before an event produces damage. Experts can also be engaged to evaluate a variety of risk transfer options (including individual insurance policies, pooled risk programs, catastrophe bonds, etc.) and present them to your finance team to inform the best decision for long-term risk management.

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• INSURANCE: For coastal flooding risks that cannot be mitigated, consider insurance products specifically aimed at alleviating the financial costs associated with flooding. More information
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  • During the design and construction phases, carefully consider purchasing a ‘builders risk’ insurance policy for your project. In particular, ensure that the policy can cover aggregate weather hazards including those related to flooding (such as wind and extreme rainfall).

  • Consider teaming with other construction efforts in a shared policy or seek government subsidy in cases where economic development is being encouraged or where recent cyclones or other perils have caused damage and a rebuilding process is underway. Look into recent flooding events and whether it has caused damage to property under construction. Speak with those construction planners to learn if they obtained insurance coverage in advance, and the cost and benefits associated with that coverage.

  • After construction is complete, plan to purchase a long-term hazard policy to protect your investment against coastal flooding, especially if it covers other significant hazards in your project area. Keep in mind multiple location policies can be an economical means of covering diverse risks across multiple locations. During financial planning, budget such a policy and prepare for potential premium increases resulting from higher risk levels in the future (for example, from rising sea levels).

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• CRITICAL INFRASTRUCTURE: If the project involves the development of critical infrastructure (e.g., a hospital, fire station, or power transmission line), or will support critical infrastructure, you should consider how your project can be affected by coastal flooding that occurs outside of the specific project location. More information
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  CONTEXT:

  • For projects that relate directly to critical infrastructure (such as a hospital project, utility expansion, or communications facility), there is a greater need for the assets to function post-event either to maintain essential services or to provide emergency response and recovery efforts.

  • Most projects (even unrelated to infrastructure) rely upon public services such as electricity, water, communications, etc. and provide services or products that are important to the local, regional or national economy and commerce. Thus, even when the project itself is not damaged by the impacts of coastal flooding, it may not remain functional due to disruptions in critical infrastructure. The chain of supply of these critical services should be considered and contingency plans developed for each service (e.g. water, electricity, transportation networks). In particular, if the project is for infrastructure development (e.g., a new electrical sub-station), its connection to the wider service network should be planned for carefully.

  • Damage and disruption to the local transportation network may not disrupt the functioning of a facility, but it can prohibit personnel from reaching critical infrastructure or an emergency facility.

  MITIGATION:

  • Consider all dependencies on your project that are vulnerable to coastal flooding. Consider redundant (backup) systems whenever possible, in conjunction with your key service providers. For example, in the event of a power outage, does the budget support housing backup generators and, if not, what would be the most likely electrical service available? If power were lost for 1 day, 1 week, etc. what would be the financial impact? Are there insurance products that can protect the project from such an interruption (see insurance section)?

  • Be wary of the location of emergency response equipment, in particular electrical generators. Conduct cost/benefit analysis to determine if on-site backup power generation is an option within the budget. Generators stored in the first story or basement will likely be inaccessible. Even if the equipment is accessible, it may be damaged or completed inoperable at a time when it is most needed. Expect a prolonged period of power loss and carefully consider your ability to generate power within your overall Emergency Response Plan.

  • Conduct cost/benefit analysis to determine if on-site backup power generation is an option within the budget. Independent wireless communication (e.g., VHF) radio may be a cost-efficient option for communications redundancy and prove vital in a time of crisis. Expect loss of communications in a major coastal flood event.

  • If roads and transportation access are important to the project, either for on-site staff or for post-event operations (e.g., ambulance service) consider alternative routing, or if the risks are high, an alternative site for the project.

  • Play out disaster scenarios (scenario planning) on your project to stress such conditions and to plan how to respond.

  • Flooding will reduce or completely eliminate your main access routes in and out of the project site. If roads and transportation access are important to the project, either for on-site staff or for post-event operations (e.g., ambulance service) consider alternative routing, or if the risks are high an alternative site for the project.

  • Dependencies to infrastructure are often difficult to manage. If the dependencies are high and the cost of mitigation and redundancy are over budget, consider an alternative site for the project.

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