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Flood Control Measures

Introduction

While the nations are competing to improve their economies, monsoon nights have become nightmare for the communities drowning in flood. Many nations are suffering from periodical floods every year. Floods worldwide have killed more than 500,000 people and displaced 650,000,000 people over the last thirty years.

Large scale floods had displaced a minimum of 100,000 people annually over 1,800 cities in 40 countries during years 2003-2008. Cities in the low elevation areas are 3-4 times more likely to be affected by the large floods due to heavy rainfall and rising sea level. Major urban flooding in the last decade affected Mumbai, New Orleans, Yangon, Dresden, Rio de Janeiro and Pakistan.
Despite rainfalls, over 700 million people in 43 countries are suffering from water scarcity, it is estimated that by 2025 this number will further rise to 1.8 billion, living under water stress conditions.

With the alarming rate of climate change and rising sea levels urban floods are expected to be more frequent, particularly in tropical regions. Few coastal cities are likely to face water scarcity as well as prone to floods.

Cause of Flooding:

There are numerous causes of flooding. Few of them include:

  • Heavy rainfalls
  • Shrinking water bodies
  • Illegal occupation of land over the lakes, riverbeds.
  • Lack of proper Drainage
  • Development and exploitation of wetlands
  • The ratio of higher grey infrastructure to green infrastructure.

Though some causes are natural, most of them are a direct outcome of human intervention. It is need of the hour for India to have “urgent and improved” water management systems, flood management being one of it.

Solutions for Flood Control:

Re-afforestation, afforestation and forest conservation:

  • Establishing trees over the land where there was history of previous forest cover
  • Reduces the occurrence and intensity of floods
  • Help in stabilizing slopes in the areas of upper water sheds
  • Trees intercept rainfall and increase infiltration and ability o soil to store more water

Riparian buffers:

  • Vegetation or forest strips along the bank of rivers, streams, lakes and other water ways to protect the aquatic life from the surrounding landuse
  • Riparian buffers help to control floods, maintain water quality
  • Act as filters of pollution, filtering the nutrients from the adjacent landuse to enter into the water body
  • Improves the landscape aesthetics

riparian buffer zones

Wetland restoration/conservation:

  • Renewal of wetlands that have been lost due to exploitation of human activities
  • Wetlands support water supply, drought mitigation and flood control
  • Regulates the water quality and quantity
  • Improves the aquatic and land habitat
  • The services provided are sustainable, cost effective and additionally provide a wide range of socio-economic benefits
  • Example: Kolkata wetlands, The Muthurajawela wetlands in Sri Lanka

Construction of wetlands:

  • Artificial wetlands are constructed with and objective to attain benefits of natural wetlands.
  • Act as biological wastewater treatment plants
  • These wetlands will be able to store lager amounts of storm water runoff, proving flood control as well as water source

Reconnecting rivers to floodplains (levee removal):

  • Levees are upland strips that are constructed to protect the civilizations from floods.
  • But the levees constructed for one settlement leaves the adjacent settlement as low-lying areas, making them more flood prone with high risk factors
  • Removal of levees and creating a forest buffer in between the levee and water will help to avoid the disadvantages of levees.
  • Reconnecting the lakes, rivers to floodplains complete the habitats and water cycle, increasing the water storage and absorption capacities, improving the life around the water bodies.

Improved levees

Flood bypass:

  • Portion of floodplains that are connected to the rivers creating a room for the flood water during the precipitation seasons which result in increased water levels.
  • Improves the ground water levels
  • Helps to store water and help in formation of new enriched habitat.

Green roofs:

  • Building covered with vegetation fully or partially on the roof.
  • Also called as eco-roofs.
  • In the dense concrete forest these roofs help to increase the surface area for absorption of surface runoff, thereby reducing the accumulation of water and the chances of urban flooding.
  • Improves aesthetics, brings down pollution levels, creates small scale habitats.
  • Examples: Japan, USA, China

Green roofs

Permeable Pavements:

  • Pavements that allow the surface runoff to enter the ground.
  • Grass pavements or concrete tile pavements with gaps and green spaces allows water to be absorbed into the soil increasing groundwater levels.
  • Solves the water logging problem which often leads to urban flooding

Water Harvesting:

  • Storage and redirection of rainwater and storm water runoff.
  • There are multiple techniques to harvest rain water with respect to catchment area, terrain, climate and the rate of precipitation
  • Flood mitigation due to the reduced storm water runoff

Protection or restoration of mangroves, marshes and dunes:

  • Reduce vulnerability of coastal settlements and also is source of income and livelihood for millions of people.
  • Due to the climate change, resulting in rise of sea levels post a threat of these coastal regions to be submerged, the mangroves, marshes help to reduce the impact on the coasts.
  • Examples of flood control projects: China’s sponge city – Wuhan, Bicester – England water management with interventions of green infrastructure

Spong city flood control

Author:

Dara Rithvika
Member of NOSPlan
School of Planning and Architecture, Vijaywada