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Evaluating mitigation measures for floods
Remember to write on both the benefits (success) and challenges (limitations) with NAMED examples.
Regulations:
Zoning
Zoning laws specify the areas where residential, industrial, commercial or recreational activities may take place. Flood-prone areas are often zoned as low-value developments such as parks and fields for recreational activities so that fewer economic losses will be incurred in the event of floods.
It creates space for green areas such parks and fields which help reduce the impact of flood damage.
However, zoning may limit the development of available land because only certain uses are permitted. It is also difficult to carry out because of competing land uses and people may not abide by the recommended land use.
Named example: Eagan City in Minnesota, USA.
Areas near the flood-prone Minnesota River are used for low-value developments such as the Minnesota Valley National Wildlife Refuge and parks.
Industrial zones and residential zones are located further away from the river so that factories and houses may be safe from floods.
Elevating properties
Properties are elevated or raised to a certain height to prevent floodwaters from entering properties during a flood event.
Properties are protected from flood water up to a certain height.
However, it is challenging to implement because of the increased cost of development. The appearance of or access to building may be badly affected. Floodwater may exceed the minimum height at which properties are raised.
Named example: Singapore
The minimum platform level (MPL) is imposed on new and existing developments. A series of slopes or steps are built to meet the MPL requirements.
In areas with no flood history, the MPL is 300 mm above the adjacent road or ground level.
In areas with a flood history, the MPL is 600 mm above the highest recorded flood level.
Investment in Infrastructure:
Levees and floodwalls
Levees are raised banks which can be natural (made of mud) or man-made (made of concrete).
Floodwalls are man-made structures that are made of concrete.
Both levees and floodwalls are barriers that are built higher than floodplains and rivers so that they can help keep out floodwater or prevent flooding.
It is a cheaper options to mitigate and prevent floods as compared to raising the height of the surrounding land.
However, levees and floodwalls need regular maintenance to ensure that they are strong enough to hold back floodwater. In addition, they are designed to hold back floodwater only up to a certain level. Beyond that level, they are unable to prevent floods.
Named example: Sacramento, USA
In the 1870s, several kilometres of levees have been built along the Sacramento River to protect the surrounding land from floods.
Named example: Hereford in Herefordshire, UK
In 2008, a floodwall was built along River Wye to protect the city from flooding during heavy rains.
Channel improvement
This makes it possible for moderate- to high-value developments to take place on the land adjacent to channels and canals. Larger amount of water can be carried away.
However, channel improvement may create problems for areas upstream or downstream of the improved area. Prolonged and intense rainfall will also cause the capacity of the channels to be exceeded. It is also difficult to carry out when the land next to the river channels and canals is already used for other purposes.
Named example: Singapore
A section of the Bukit Timah Canal was widened and deepened to increase the channel capacity.
Disaster Preparedness:
Forecasting and warning systems
Water levels in river channels and canals, tide levels in seas and surrounding weather conditions are monitored regularly using manual monitoring systems and technology (eg. remote sensing techniques & geographical information systems).
The information collected is then analysed to make a flood forecast on the areas that are likely to be flooded.
Subsequently, flood warnings are issued to the public via social media, television and radio so that people can take necessary precautions in advance.
This provide useful information so that there is time for people to take action to minimise flood damage.
However, some cities may not have the expertise and technology to collect accurate data and are unable to make accurate flood forecasts.
Named example: Singapore
Water level sensors are placed in canals and drains to gather data about the changing water levels at regular intervals.
Weather instruments are used to monitor the tides and weather conditions on a daily basis.
Evacuation drill
A form of preparedness measure where people practise the steps to leave a place in a safe and orderly manner during an emergency.
It involves people moving to safe locations by following instructions given by trained personnel and practising first aid. It creates awareness among the people and reduces panic during a flood event. It will enable the government to improve their flood evacuation plans.
However, limited participation from the public will reduce the effectiveness of the city’s evacuation plan.
Named example: Singapore
PUB has provided a public advisory on what pedestrians, motorists, residents and business owners can do in the event of a flash flood.
Channel improvement
Enhancing Singapore's drainage system
The need to mitigate floods in Singapore
https://mothership.sg/2020/09/bukit-timah-canal-heavy-rain/
2 measures to mitigate flood as mentioned in the article in response to the heavy rain on 12 Sept
Channel management
Prediction and warning
Are you able to describe the measures and evaluate on their benefits and challenges?
Click on the link below to read the latest updates on Singapore's stormwater management strategies:
The Stamford detention tank below the botanic garden helps to prevent flooding in Orchard road.
Using flood gate to alleviate flooding @ Marina Barrage:
Japan's underground flood defence system
Forecasting and evacuation
Watch the video how forecasting can reduce flood risks in UK.
Evacuation drills
Watch how emergency drill is conducted in preparation of floods in China
• It creates awareness among the people and reduces panic during a flood event.
• It will enable the government to improve their flood evacuation plans.
Flood defence infrastructure
Coastal embankment in Bangladesh
Levees along Yangtze River
Evaluating mitigation measures for floods in Singapore:
Minimum platform level:
Minimum platform levels raise buildings to a certain height so that buildings will be protected from floods up to that height.
However, implementing this is challenging and costly for existing developments and built-up areas.
Expansion of canal:
Drainage channels can be expanded so that more water can flow through easily and quickly. This will help prevent storm water from building up
and causing floods.
However, there may not be enough land area to increase the size of the canals further.
Flood barriers:
Flood barriers keep water from entering the facilities and shops
However, the barriers can only keep out floodwater up to a certain height.
Evaluating mitigation measures for floods in Manila:
Increase the height of the floodwall
In the event the height of floodwater increases, the higher floodwall may keep ut the floodwater.
However, it is not able to keep out floodwater that exceeds the height of the floodwall.
Only allow certain land use near rivers
It will reduce losses when only low-value development are located near the rivers.
However, land use further away the river will be affected in the event of a major flood that affects a huge area.
Ensure all new buildings are elevated to a certain height
It will help protect buildings up to a certain height.
However, buildings will be affected if floodwater exceeds the stated height.
Construct bigger channels
The bigger channel will hold and enable a large amount of water to flow through.
However, there may not be enough land area to increase the size of the canals further.
Carry out regulations to ensure our channels are free of rubbish
It will enable water to flow more smoothly.
However, prolonged and intense rainfall will cause the capacity of the channels to be exceeded.
Interesting way to manage flooding with park design in Bangkok
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