Impact of Dredging in Restoration of Lakes

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Dredging is emerging as a common technique in efforts to restore the ecology of lakes. However, according to a recent study conducted on Lake Manjala, this process can lead to unpredictable and sometimes irreversible changes in the micro-ecology of the lake.

About Dredging

• What it is: The technical process of removing silt, sand, sediment, debris and other substances from the bottom of a reservoir, lake, river, harbor or seashore with the help of machines
•  Purpose: Usually to increase the depth of a water body, improve water flow, facilitate navigation or clean polluted sediments
• Key techniques:
  • Mechanical dredging: Removing sediments with machines such as cranes or draglines
  • Hydraulic dredging: Dissolving sediments with high-pressure water and then removing them through pipelines
• Benefits:
  • Deepening waterways: Ease in movement of ships, boats and other watercraft
  • Flood control: Reduce the risk of floods by increasing the flow capacity of streams
  • Pollution control: Removing pollutant-rich sediments deposited at the bottom of a lake or river
  • Increasing the capacity of a lake/river: To improve water storage and flow
  • Land reclamation: Creating usable land by removing sediments from the sea or river

Key findings of a recent study on Lake Manzala

• Researchers at the Cairo-based National Institute of Oceanography and Fisheries The study studied Egypt's coastal Lake Manzala for seven years during 2015-2022.
•  Researchers claim that after dredging, the lake's storage capacity will increase to 903.64 million cubic metres (MCM) in 2022 from 378.67 MCM in 2016.
• However, the lake's water quality and ecosystem have changed significantly after dredging. Due to dredging, salinity in the lake has increased significantly and nutrients have decreased in 2022 compared to 2015.
• According to the study, the maximum salinity of the lake after dredging increased by 73% from 2015 to 2022.
  • As a result, chemical parameters and zooplankton have changed in the northern and central regions of the lake. The number of zooplankton has decreased overall but the population of saltwater species has increased in the year 2022.
  • Additionally, changes in the chemical properties of water have led to an increase in saltwater species of zooplankton and a decrease in freshwater species.
• According to the report, there has been an overall decrease in biochemical oxygen demand (BOD) and chemical oxygen demand (COD).

About Lake Manzala

• Location: Lake Manzala is Egypt's largest coastal lagoon located along the Mediterranean Sea, in the northeastern part of the Nile Delta.
  • It is also called Manzaleh.
  •  Lake Manzala is the northernmost of the three natural lakes cut by the Suez Canal. The other two lakes are 'Lake Timsah' and 'Great Bitter Lake'.
• Environmental importance: This lake is the natural habitat of various types of fish, aquatic species, birds and plants.
  • This lake is formed by the confluence of salt water and freshwater streams of the Mediterranean Sea, which creates a unique ecosystem.
• Economic importance: This lake contributes significantly to the economy of Egypt, especially in terms of fisheries, local trade, agriculture and employment. According to the data of the year 2021, this lake contributes 16% to the total natural fish production of Egypt.
• This lake is a source of moisture and water recharge for the surrounding agricultural land.
• Flood control: This lake acts as a natural buffer zone between the sea and agricultural land, which protects against flooding during heavy rainfall or sea tides.