GED 2247 Ecology: Natural Disasters Lecture Notes PDF

GED 2247 ECOLOGY Lecture: 23,24 NATURAL DISASTERS Prepared by, Nabid Hasnat Adjunct Faculty Department of Civil Engineering Leading University Flood Flood ▪ Flood is an overflow of water that submerges land that is usually dry. This can happen due to various reasons such as heavy rainfall, riv...

GED 2247 ECOLOGY Lecture: 23,24 NATURAL DISASTERS Prepared by, Nabid Hasnat Adjunct Faculty Department of Civil Engineering Leading University Flood Flood ▪ Flood is an overflow of water that submerges land that is usually dry. This can happen due to various reasons such as heavy rainfall, river overflow, tidal waves, or the breaking of dams. Floods can cause significant damage to property, infrastructure, and can even lead to loss of life. ▪ Bangladesh is a riverine country with around 700 rivers flowing through it, out of which, 57 are transboundary rivers. The Ganges, the Brahmaputra, and the Meghna are combined known as the GBM basins, and 80% of the total rainfall occurring over the basins during the summer monsoon season, leads to a huge volume of transboundary runoff and are responsible for most of the floods in Bangladesh. 01 Causes of Flooding in Bangladesh: 02 Causes of Flooding in Bangladesh: ▪ Low general topography ▪ High monsoon flood through principal channels ▪ Siltation of the principal distributaries ▪ Overbank spilling of the rivers ▪ Flood control measures in upper reaches ▪ High rainfall ▪ Backwater effects of tides of Bay of Bengal ▪ Rise of the mean sea level (MSL) ▪ Topographic features controlled by geological factors ▪ Earthquake ▪ Peak flood synchronization in the Ganges & the Brahmaputra 03 Primary Effects of Flood 04 Secondary Effects of Flood 05 Flood Mitigation Strategies (Structural Measures): ▪ Flood embankments: Flood embankments serve as earth-fill structures to restrain elevated water levels and protect lands from inundation. Using locally sourced materials in their construction helps reduce expenses and ensures minimal environmental impact. ▪ River dredging: Sedimentation is a natural process in which sand, silt, and debris are deposited at the bottom of water bodies, such as rivers. Such accumulation of materials in the riverbed can reduce the depth of the water bodies and restrict their water-holding capacities. This phenomenon can lead to significantly increased chances of flooding. Dredging is the removal of built-up sediment from the bed or sides of the body of water, such as rivers, by scooping out. Dredging can potentially return a waterway to its original depth and condition by removing the debris buildup, thus enabling it to effectively manage the natural water levels within its watershed, preventing overflow onto adjacent land. Consequently, the risk of flooding is reduced. 06 Flood Mitigation Strategies (Structural Measures): ▪ Improved drainage system: Flooding can be experienced when there is heavy rainfall, but the number of drains is inadequate, or their discharge capacities are surpassed. Properly designed drainage systems would ensure that stormwater is discharged effectively, which, in turn, could warrant minimized property losses and recovery expenditures. Green infrastructure may preserve natural drainage flow by preventing the direct entrance of stormwater into conventional drainage systems. Fishponds can serve as water retention ponds. Other effective measures include increasing the drainage capacity, constructing pumping stations, and building flood diversion culverts. ▪ Flood-resilient housing: Houses made of poor-quality materials are severely damaged during flash floods. These houses must be repaired or rebuilt after the flood retreats. Therefore, the houses fail to serve their purpose of providing shelter to their occupants and prove to be a waste of money. A simple solution would be to spend more considerable sums a single time to build a house resistant to most floods. This purpose can be easily served by using higher foundations and flood-resilient materials. A plinth level of at least 900 mm is recommended to protect the houses from flood water as well as storm surges. 09 Flood Mitigation Strategies (Non-Structural Measures): ▪ Flood early warning system (FEWS): Early warning systems consist of hazard monitoring, forecasting, and prediction, as well as disaster risk assessment, communication, and preparedness activities. This integrated system enables individuals, communities, governments, businesses, and others to mitigate disaster risks before hazardous events occur by taking proactive measures, which consequently helps save lives and diminish the economic impact of natural hazards. Improving meteorological services can help deliver quick and precise weather forecasts, predict rainfall, and generate flood warnings. Bangladesh can improve its early warning systems by integrating satellite data, remote sensing, and enhanced weather models. Setting up community-based early warning systems with the help of local networks like radio, mobile phones, and community leaders can spread flood alerts quickly and effectively. Institutions responsible for flood forecasting and agencies responsible for issuing warnings and notifying communities, ensuring preparedness and awareness, must work together. It should be confirmed that the communities understand the significance of FEWS and support it throughout. This can be achieved by taking initiatives to promote social awareness, conducting regular post-disaster surveys to gather feedback from the targeted communities, and developing response and evacuation plans tailored to each specific community. 10 Flood Mitigation Strategies (Non-Structural Measures): ▪ Land-use planning and zoning: One of the effective flood-mitigation policies is establishing and implementing land-use policies that prevent construction in flood- prone areas and encourage the practice of agricultural activities or other low-risk and environmentally sustainable works in the floodplains. Another important consideration is the enforcement of zoning laws that restrict development activities in high-risk flood zones and promote the creation of buffer zones to absorb and slow down floodwaters. ▪ Wetland preservation and afforestation: Although floods are natural, some human activities increase flood vulnerability, such as deforestation and eliminating natural water reservoirs by landfilling or reducing their water-holding capacity by waste dumping. One of the simplest strategies for delaying floods and reducing their impact is the preservation of wetlands, which act as a buffer against floods, digging ponds, and planting trees and vegetation along the river banks that reinforce soil against erosion and increase their flood resistance. 11 Flood Mitigation Strategies (Non-Structural Measures): ▪ Flood risk assessment and data sharing: Conducting regular risk assessments and conducting research is significant for understanding the changing flooding patterns and evaluating the effectiveness of existing mitigation measures. To achieve this, platforms can be created for sharing flood-related data that stakeholders, including government agencies, researchers, and the public, can access. ▪ Awareness campaigns and community training: Another important flood preparedness strategy is educating the community about flood risks, preparedness measures, and safety procedures. These campaigns can include workshops, school visits, training programs, and media outreach. ▪ Evacuation and participatory planning: Developing comprehensive evacuation plans that outline clear safety protocols for removing people from their residences and taking them to shelters during a crisis can help save them from life threats and diseases. Training and equipping the local authorities and emergency responders in flood response and management activities while establishing coordination with national and international agencies can help achieve this. Engaging local people in preparing flood preparedness strategies can help save time and resources as they are more aware of local needs and can access local information. 12 Cyclone Cyclone ▪ The word cyclone comes from the Greek word Cyclos which means coil of snake. ▪ A cyclone is a large air mass that rotates around a strong center of low atmospheric pressure. ▪ Cyclones are characterized by inward-spiraling winds that rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. ▪ Cyclones can cause severe weather, including heavy rain, strong winds, and flooding. 13 Causes of Cyclone: ▪ Warm Ocean Waters: Cyclones form over warm ocean waters near the equator. The warm, moist air above the ocean rises, creating a low-pressure area at the surface. ▪ Low-Pressure Zones: As the warm air rises, it cools and condenses, forming clouds and releasing latent heat, which further warms the surrounding air and causes it to rise. ▪ Coriolis Effect: The rotation of the Earth causes the rising air to spin, which helps in the formation of the cyclone. This effect causes the cyclone to rotate clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. ▪ High Humidity: Increased humidity in the lower to middle levels of the troposphere provides the necessary moisture for cloud formation and intensification of the cyclone. ▪ Low Vertical Wind Shear: Low wind shear allows the cyclone to grow vertically without being disrupted by strong winds at different altitudes 14 Why Bangladesh is Vulnerable to Cyclone? ▪ As Bangladesh is located in the Torrid Zone, cyclone is very common here. In the Torrid Zone (or tropical Zone or Tropic) the Sun is directly overhead at least once during the year. Geographically, the torrid zone is defined by 23.5 degrees north latitude and 23.5 degrees south latitude. The tropical zone contains the areas those are the hottest places on earth. ▪ Most areas within the torrid zone receive plenty of rainfall to promote lush vegetation growth with the aid of the sun directly overhead. The temperature stays relatively uniform from day to night. Cloud cover helps keep the temperature uniform throughout the day and through the seasons. This very same cloud cover also promotes almost daily rainfall during the wet season. When warm moist air rises and is coupled with ground heating by the sun, this causes atmospheric disturbances resulting in thunderstorms. Prevailing winds in the tropics tend to blow from east to west, often causing deserts to be located on the western side of major continental masses. ▪ The Bay of Bengal is the breeding sea for tropical cyclones. Presence of the sun over the region during the periods feeds the required sensible heat, the bay water maintains the critical ocean temperature of 26-27°C needed for cyclone generation, sustain and intensify. Most of the devastative cyclones in human history formed in this bay. 15 Cyclone Preparedness (Structural Measures): ▪ Siting or re-siting of buildings might be considered in locations with minimal exposure to high-velocity winds, floods & surge prone zones ▪ Special cyclone-resistant building materials/ patterns should be used ▪ Cyclone shelters should be constructed with flood-proofed access routes ▪ Construction of multi-purpose, multi-story concrete structures should be ensured ▪ There should be no house between two mountains ▪ Wind load must be calculated before the construction of any structure ▪ For high-rise buildings steel structures/ towers are to be provided for upper floors (as they are more ductile than concrete). ▪ The span of bridges must be combined with separate short spans instead of a single long span ▪ Coastal embankments should be constructed 16 Cyclone Preparedness (Non-Structural Measures): ▪ Land-use zoning ▪ Warning systems ▪ Emergency agencies, facilities and equipment ▪ Community education ▪ Coastal forestry planning with appropriate mangrove species & vegetation on the embankment 17 Cyclone Warning System 18 Earthquake Earthquake ▪ An earthquake is an unpredictable event in which masses of rock shift below Earth's surface, releasing enormous amounts of energy and sending out shock waves that sometimes cause the ground to shake dramatically. Not all earthquakes are enormous, but they can become one of Earth's most destructive forces. ▪ Magnitude is a quantitative measure of the actual size of the earthquake. An earthquake that measures 8 or above on the Richter scale causes total damage. ▪ Intensity is a qualitative measure of the actual shaking at a location during an earthquake, and is assigned as Roman Capital Numerals. The scales range from I (least perceptive) to XII (most severe). The intensity scales are based on three features of shaking – perception by people and animals, performance of buildings, and changes to natural surroundings. 19 Seismic Waves ▪ The vibrations transmitting the shock of an earthquake are called seismic waves. These waves travel outward in all directions, like ripples from a stone dropped in a pond. ▪ The area where energy is first released to cause an earthquake is called the focus. The focus lies underground at a shallow, intermediate, or deep depth— down to about 430 miles (700 kilometers). ▪ The epicenter is the point on Earth's surface, usually almost directly above the focus, where the seismic waves of an earthquake first appear on the surface. 20 Causes of Earthquake There are many causes for earthquakes. Movement on the Earth's crust, volcanic eruptions and man made explosions are some. Earth's crust is composed of many huge, rocky plates known as tectonic plates. These plates constantly move slowly across the surface of Earth, bumping into each other, overrunning each other, and pulling away from each other. Usually, the movement is gradual. At other times, the plates are locked together, unable to release the accumulating energy. When the accumulated energy grows strong enough, the plates break free causing ground-shaking vibrations associated with an earthquake. So, an earthquake is a sudden movement of the Earth, caused by movement between tectonic plates. 21 Earthquake in Bangladesh ▪ Bangladesh is one of the most earthquake prone countries in the world. Since the whole Indian subcontinent is situated on the junction of Indo- Australian plate and Eurasian plate, the tectonic evaluation of Bangladesh can be explained as a result of collision of the north moving Indo- Australian plate with the Eurasian plate. ▪ Besides, there are several fault zones active in this junction area, which are the sources of earthquake. Four major sources of earthquakes in and around Bangladesh were identified by Bolt (1987): i) Assam fault zone ii) Tripura fault zone iii) Sub Dauki fault zone and iv) Bogra fault zone. ▪ Specialists are expecting a severe earthquake in this area in near future, which will cause a serious human casualty, damages of infrastructure and other losses. ▪ Although Bangladesh is extremely vulnerable to seismic activity, the nature and the level of this activity is yet to be defined. In Bangladesh complete earthquake monitoring facilities are not available. The Meteorological Department of Bangladesh established a seismic observatory at Chittagong in 1954. This remains the only observatory in the country. 22 Probable Effects of Earthquake (a scale of M6.5 or above) in Dhaka: ▪ Panic among the city dwellers and no knowledge of what is to be done during and immediately after the eq. occurrence. ▪ Possible sinking of many of the buildings on filled earth with shallow foundations due to the liquefaction effect. ▪ If the eq. occurs during monsoon time possible damage of the Dhaka flood protection embankment due to liquefaction effect causing sudden submergence of a large area. ▪ Large scale damage and some collapse of poorly constructed and/or old buildings. ▪ Possible outbreak of fire in most of the buildings from the gas lines (the residential ovens are mostly in burning condition from morning to mid-night). ▪ Possible damage of power installations and power cut off for indefinite period. ▪ Water supply failure as almost all the deep tube wells are run by power, and possible water line damage. 23 Probable Effects of Earthquake (a scale of M6.5 or above) in Dhaka: ▪ Damage of roads and blockage of traffic due to falling of debris from collapsed buildings and other installations on or near roads. ▪ Some of the hospital buildings may collapse killing a large number of inmates and stopping medical facilities for the disaster victims. ▪ Some of the school building may collapse killing and injuring a large number of students. ▪ An after shock may cause further collapse of many of the already damaged buildings. ▪ A few rescue equipment, whatever are available, can not be operated due to the lack of guidance, availability of operators, some will be non-functional, some will be under the rubbles, some can not find access to rescue spots due to road blockage, etc. ▪ Limited access from outside as most or the highways/bridges, airport will not be functional. 24 What is an early warning system for earthquakes? Basically, sensors that can detect weaker P waves. These signals are detected and processed through advanced computer algorithms to determine the location and magnitude of the earthquake. The time given to prepare depends on the location’s distance from the epicenter. If its under 50 km, then this time is less than 10 senods. 50-100km this turns to around 30 seconds, and more than that it can range up to a minute. Benefits ▪ Immediately brace against the earthquake. ▪ Turn off gas-lines and slow down trains or other vehicles. Implementation Mobile warning: Earthquake notification. This is already in application to some extent as Google gives an early warning. This can be done through a government-controlled warning system that directly gives warnings through SMS. Building warning system: Important buildings should have a special alarm that receives those warnings and can warn us just as a fire alarm would. Building Emergency Response Systems: Buildings should have systems that automatically shut down utility lines such as electricity and gas lines. 25 SELF STUDY: Write about the causes and mitigation strategies involved in Floods, Cyclones and Earthquakes briefly. Try to remember the core aspects and write about them in your own way. 26 Thank you Any questions?