 1 - Oil spilling accidents in wetlands 
2 - Impact of oil pollution in water environment
- An already long series of events at sea and in rivers
- A key parameter is prevention is "effective" enforcement of good engineering practices and standards
- Next important is accurate prediction of the extent and speed of pollutants spreading
- Well organized contingency plans for efficient intervention
- Cleaning and remediation can take years …
3 - The Doba/Kribi pipeline
Some key elements :
- Total length is 1050 km (ex : Alaska : 1600 km)
- Maximum capacity : 250 000 barrels/day
- Buried at a depth of 1m
- Special measures when crossing waterways : increased burial, reinforced trenches, bridging
- Stop valves every 35 km
- Centralized automatic control (SCADA) : 24h/24h
- Control centre : Houston, USA (main) and Douala
- Contingency headquarters : Douala, Cameroon
4 - Environmental risks during operations
At the rigs :
- Explosions followed by spillage
- Uncontrolled leakage followed by spillage
Along the pipeline route :
- Leakage in buried sections with water table pollution
- Accidents at waterways crossing with spillage in river
- Crossing by heavy animals with damage(ex : elephants)
- Accidents following « siphoning » (ex : Nigeria, Poland)
- Damage by agriculture and construction works
Pre Doba project environmental impact study by Dames & Moore. Contingency plan defined in World Bank environmental study.
5 - Searching for models on the Internet
6 - The River Time-of-Travel (R-TOT) migration model
Oil migration processes are multiple :
- Convection (or transport)
- Diffusion
- Adsorption
- Degradation
All these factors are influencing both the efficiency of oil dispersion in water and its dilution rate The R-TOT model :
- Uniform stream flow
- Transport model (convection) + dispersion (gauss distribution)
- Predicts time of passage and peak concentration downstream
- Only needs river discharge data
7 - Comparative flow rates for world rivers
- Mississippi : 20 000 m3/sec – Normal flow
- Rhine river : 1000 m3/sec at Bâle and 2200 m3/sec near mouth in North Sea
- Mekong : 15 000 m3/sec – Normal flow
- Chari-Logone : 4000 m3/sec in yearly looding conditions
8 - Running RTOT
An Excel based tool.
- Basic parameters :
- Spill start and end along stream (in miles)
- Spill amount (in barrels) [1 barrel = 0.16 cubic meters]
- Discharge (in cfs)
Possible use of unit converter at http://www.df.lth.se/~thanisa/recept/units.html
Simulations :
- Logone / Chari rivers - Flood flow rate= 4000 m3/sec. Answers : 7 days to spread from Laï to Bongor (150km) followed by uncontrolled dispersion in inner delta wetlands
- Mississippi river - Normal flow = 20000 m3/sec. Answers : 1 day to travel 150km during heavy flooding !
9 - Spillage costs compared
- Exxon Valdez : 260 000 barrels – US$ 900 Million
- San Jacinto : 35 000 barrels – US$ 23 Millions
- Shell Nigeria : 36 000 barrels - Pipeline explosion
10 - Oil spilling scenario for the extended Doba/Kribi project
Catastrophic rupture of pipeline in the Logone area (ex : Laï). Evaluation is based on the fact that at full capacity, the pipeline would hold 250 000 barrels of oil for a
total length od 1050 km with one stop valve every 35 km.
See
actual spec. data ...
- Spilling of total oil volume contained in pipeline section separated by two stop valves ( 35*250000/1050 = 8333 barrels).
- Delay in contingency plan deployment adds a multiplicative factor. Optimist hypothesis : 10000 barrels
- Estimated costby comparison with existing past incidents : US$ 30 Million if flood plain is reached but pollution under control within 15 days.
The particular case of Logone-Birni (North-Cameroon)
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