Final degassing plan: the total eradication of a natural hazard

 

 

Instrumentation

Monitoring of the diphasic stream

  • Liquid flow rate
  • Liquid speed
  • Depth of the column foot
  • Pressure at different depths
  • Differential of temperature (cooling of the water)
  • Axial strength on the column (level of the raft)

Surveillance of the de-stratification

  • CO2 dissolved concentration:
  • liquid flow rate
  • gas flow rate
  • Conductivity
  • Temperature

Fundamental parameters

  • Temperature of the bottom of the lake
  • Temperature gradient in the sediments

Meteorology

  • Rain gauge
  • Air temperature
  • Suface lake water temperature
  • Lake water level
  • Flow rate at the spillway
  • Temperature of the stream feeding the lake from the South

Technological parameters

  • Battery levels
  • Pressurised bottle pressures

 

  

 

 

 

Degassing schedule

Nyos

Composition (1992) :

  • Layer 40 - 170 m :
    • Water : 105 Mm3
    • Gas: 190 Mm3
  • Layer 170 - 208 m :
    • Water: 17.5 Mm3
    • Gas: 80 Mm3 (1992)

5 pipes at 205 m, internal diameter = 139.8 mm;
Liquid flow rate 2 Mm3/year/pipe

Conclusion: after 3 to 5 years, the situation will be safe.

Monoun

Composition :

  • Layer 30 - 60 m :
    • Water : 4.75 Mm3
    • Gas: 3.65 Mm3
  • Layer 60 - 96 m :
    • Water: 2.1 Mm3
    • Gas: 5.8 Mm3

3 pipes, internal diameter = 102.2 mm
Liquid flow rate 0.8 Mm3/year/pipe

  • Step 1: depth 70 m; 1 year,
  • Step 2: depth 80 m; 6 months,
  • Step 3: depth 95 m; 6 months.

Conclusion: after 2 years, the lake will be safe.