NYOS-MONOUN
DEGASSING PROJECT
Report
of the January 2001 Lake Nyos Pipe Installation
Presented by a Joint Cameroonian-French-Japanese-USA Team (List
of participants attached) EXECUTIVE SUMMARY (1) The initial degassing phase of Nyos-Monoun-Degassing-Project (NMDP) began at Lake Nyos in January 2001. A remotely controlled degassing system was installed, and degassing was successfully tested on 30 January. Permanent, automatic operation commenced ~2 months later. This system will offset any further increase of CO2 in the lake, resulting in reduction of the risk of another gas explosion. However, the rate of gas removal by a single pipe is insufficient to reduce the CO2 content in the lake to a safe level within a reasonable time span of 5-10 years. Therefore, additional funding is needed to increase the number of the degassing pipes to accomplish the goal of making the lake safe. (2) Early warning gas detection systems were installed at both Lakes Nyos and Monoun. The systems monitor the CO2 concentration in the atmosphere continuously and sound an alarm when a dangerously high CO2 concentration is detected. These systems contribute to the reduction of risk to the population from future gas releases. (3) Detailed information on physical, chemical, biological, and hydrological conditions of Lake Nyos were collected in order to understand the baseline of pre-degassing conditions in the lake. These data sets will be used for comparison with the future conditions of the lake as degassing proceeds. (4) Construction of the base camp (observatory and related facilities) at the lake has begun. These facilities will be useful for the maintenance of the degassing operation and the installation of additional pipes in the lake in the future. (5) There is a critical need for training of Cameroonian technicians and scientists to maintain the degassing system and to analyze the information produced by the system in order to make decisions about the continuing operation of the pipe. I.
Introduction Lakes Nyos and Monoun in Cameroon, which exploded in the mid-1980�s killing about 1800 people and thousands of livestock, still contain large amounts of carbon dioxide dissolved in their deep waters. The latest surveys indicate that Lake Nyos contains more than 500,000 tons of CO2 (270 million m3) and the gas content is steadily increasing, fed from CO2 charged springs entering the bottom of the lake (see figures in 1999 Report). Thus the danger posed by these lakes is increasing every day. The buildup of gas makes it important to estimate the likelihood of another gas burst. This can be done using the degree of gas saturation (the ratio of gas pressure to hydrostatic pressure) at various depths in the lake. The January 2001 field results indicate that in Lake Nyos there has been a gas pressure increase at all depths below 170 m compared to previous measurements. The largest increases have occurred in the bottom 20 m of the lake. Gas pressure at lake bottom exceeds 15 bar, which represents ~70% of the saturation value based on an ambient hydrostatic pressure of 21 bars. The fact that present day gas saturation is less than 100% does not indicate that the lake is safe. Any large disturbance of the water column such as a landslide, rock fall, or violent storm could trigger a release of the gas remaining in the lake. Thus another lethal gas burst could occur at any time without warning. For these reasons the Government of Cameroon initiated the Lakes Nyos and Monoun Degassing Project (NMDP), supported by an International Advisory Committee of 8 scientists and various funding sources. Successful tests of a degassing system at Lake Monoun in 1992 and Lake Nyos in 1995 led to this first phase of NMDP degassing that started in January 2001. This phase had three main goals: (1) install one permanent degassing pipe at Lake Nyos; (2) install CO2 monitoring stations at Nyos and Monoun; and (3) collect baseline data on the physical, chemical, and biological conditions in the lake before the ecosystem is disturbed by the degassing processes. This operation was financially supported by the Government of Cameroon, the U.S. Office of Foreign Disaster Assistance (OFDA), and the French Embassy in Cameroon. The overall project can be divided into several categories, and brief descriptions of each category are presented in the following sections of the report. II. Construction of
degassing system
The NMDP Advisory Committee met in Paris in March 2000 to discuss the
most appropriate methodology for degassing, and adopted the method used
by M. Halbwachs and his team in the 1995 degassing experiment at Lake
Nyos. The pipe used in this
method is made of polyethylene, a material that combines several
important advantages, including the following: (a) very pliable
(lengthening above 200% at break point), (b) neutral buoyancy (density
0.96 g/cm3), and (c) easy to cut and weld. Because of these properties, the pipe can be transported to
the lake in manageable lengths, assembled on shore, and conveniently
floated out onto the lake surface for deployment.
Once deployed and in operation, the pipe can flex under applied
stresses instead of breaking, which could lead to an uncontrolled flow
system within a separated section of pipe submerged in the lake.
The internal diameter of the pipe is 14.5 cm.
The depth of water intake at the
bottom of the pipe was set at 203 m, which takes into consideration the
lake�s depth of 210 m, the current CO2
distribution in the lake, and lowering of the lake level during the dry
season. Three
remote-control valves were attached at the depths of 0, 100 and 140 m,
and flow rate and pressure sensors were attached at several depths on
the pipe. The
data gathered by these sensors will check the proper functioning of the
self-siphon process. If at
least two of these control parameters show a significant change from
normal conditions, the system automatically reduces the large gas-water
fountain to a smaller, less energetic fountain.
For this purpose an automatic lateral valve is attached at a
depth of 100 m. The opening
of the lateral valve will allow the external, gas-poor water to enter
the pipe and mix with the gas-rich water. This will result in a decrease of the energy associated with
the gas coming out of solution. The
water and gas jet at the mouth of the pipe at
the lake surface will thus be slowed down, and the mechanical stress on
the pipe�s structure will return to a harmless level.
At that time further inspection of the data and the system may
require that either the system be shut off, or the full-strength jet be
reactivated by shutting the lateral valve.
This real-time monitoring and manipulation of the degassing pipe
is controlled remotely by a radio-link to the observatory and an
Inmarsat satellite system which is currently in operation.
The pipe is held at the surface in a large raft that is fixed in the
center of the lake by ropes anchored to the lake shore.
Two rafts were prepared: one for the pipe and another for the
instruments such as pumps, compressors, and data transmission apparatus.
The rafts were originally assembled in Japan, tested, exported,
and reassembled at Lake Nyos by Y. Yoshida.
The column of pipe and the sophisticated control system was
constructed on site by French engineers from Data Environment
Engineering together with Cameroonian engineers from IRGM (Institut de
Recherches Geologique et Miniere) and MINMEE (Ministere des Mines, de
l�Eau et de l�Energie). Initially,
transportation of the pipe and other required materials from Douala to
Lake Nyos was delayed for 5 days due to bad road conditions between
Misaje and Lake Nyos. However,
hard work by the engineers made the construction of the pipe system
complete by 29 January, and the first degassing test was successfully
performed the next day. The
degassing system is now operating on a permanent basis. III.
Degassing Operation A. Results After a successful test run on 30 January, the degassing system was fully inspected and converted to a permanent, automated installation that is now functioning as expected. With this system functional, the initial removal rate of CO2 is estimated to be approximately 20 million m3 or 39,000 tons of CO2/year. This initial removal rate is greater than the natural recharge rate of CO2 into the lake, and thus the increase of CO2 in the lake will be offset and the amount of CO2 will be very gradually reduced. However, two points must be recognized that highlight the need for additional pipes to be installed. First, the removal rate will decrease over time as the CO2 concentration is lowered by degassing. Second, there is a tremendous amount of gas in the lake and one pipe is insufficient to remove this gas. Therefore another 4-5 pipes are required to lower the gas content to safe levels within 5-10 years. B.
Safety & Security The same safety measures that were used during the 1995 test degassing at Lake Nyos were put in place in January 2001. We met with local leaders and the population to inform them of the tests, and the Cameroonian military helped to evacuate people from low-lying areas around the lake during the initial test runs.
At Lake Nyos, it is worth noting that the areas below the lake have been
officially off-limits since the 1986 disaster.
However, in reality many local people are coming back to these
areas, and it is difficult to maintain the full evacuation of people on
a long-term basis. A
thorough sweep of the area was made when the degassing operation
commenced, and we attempted to spread the word through local chiefs and
officials that the area should remain evacuated until the gas content in
the lake is greatly lowered. IV.
CO2 Monitoring Stations An early warning system for gas detection was set up at both Lakes Monoun and Nyos. The system contains a highly reliable infra-red CO2 detector that continuously monitors CO2 concentrations in the atmosphere. Normal CO2 concentrations in air are ~0.04%, and a CO2 concentration of ~5% will extinguish a flame, meaning that this amount of CO2 in the air is dangerous for animals and people. If the CO2 concentration in the air reaches 0.5% the system automatically produces a warning to the local people by sounding a siren and flashing a red light (Fig. 5; see also the report �Technical Report On The Use Of Early-Warning Systems In Detection Of Gas Releases From Lakes�, submitted to the Cameroonian Inter-ministerial Committee on behalf of the NMDP International Advisory Committee on 1 November 2000).
Meetings were organized to educate and explain the functioning of the
system to the local people after installation of the system at both
sites. The meetings
emphasized the following points. Once they hear the siren the people should (1) move away from
the lakes toward higher ground, and (2) inform and warn other people and
notify the authorities immediately.
In addition, it is important that bush fires be eliminated near
the CO2 monitoring stations because the fires could damage
the station or cause a false alarm, and that vandalism on the stations
be strictly avoided. The CO2
stations need to be maintained regularly; training of Cameroonian
scientists to perform this maintenance was completed in January 2001. V. Baseline Scientific Measurements A.
Chemistry
and physical structure of the lake
Measuring the chemistry and physical structure of the lake is important for two reasons. First, the chemistry and the density structure determine how much gas is in the lake and how stable or resistant the lake is to the uncontrolled release of gas. Second, the controlled degassing will cause changes in the chemistry and physical structure of the lake, and it is important to monitor how these controlling parameters change over time.
Detailed measurements of temperature, conductivity, pH, dissolved oxygen, CO2 concentration, total gas pressure, gas-to-water ratios, and radon concentration were performed at various positions and depths in the lake by different researchers. This is the first time that radon measurements have been made, and the objective is to determine the recharge point or vent of CO2-charged water that supplies CO2 to the lake. The physical and chemical measurements showed that the lake is strongly stratified with several layers of different density and chemistry. In addition to the above measurements, water and gas samples were collected from various depths of the lake for later determination of the chemical and isotopic compositions. B.
Climate
Station
The climate station floating close to the degassing pipe monitors meteorological parameters such as air temperature, relative humidity, wind speed and direction, solar radiation, and rainfall. In addition the stations monitor water temperature at 14 depths and total gas pressure at two depths in the lake. The climate has an important impact on the surface water of the lake, and monitoring the climate will provide useful information about how degassed bottom water from the pipe is dispersed from the mouth of the pipe into the surface water. Continuous monitoring of water temperature and gas pressure in the lake will provide information on how the chemistry and density stratification of the lake change due to the degassing process. Because it is necessary to check this data on a more frequent basis as degassing proceeds, communication by ARGOS satellite was added to the climate station in January 2001. C.
Lake Biology
The discharge of bottom water onto the lake surface could bring about a change in the productivity of the biological community in the surface water, or a change in the biological community of species itself. This is because the bottom water contains high amounts of mineral nutrients such as nitrogen and phosphorus that are required for plant growth. Background information on the biological community has been collected over many years, and in January 2001 additional measurements were made of the primary productivity of the lake. D.
Hydrology of the Lake Basin
A systematic study of the hydrology of the Lake Nyos basin was initiated
in January 2001. Water
discharge measurements were made on the inflow and outflow streams, and
permanent water level markers were installed to help indicate the flow
rate at the inlet and outflow streams.
A marker to record the level of the lake surface has been
monitored for several years by local people.
The information on inflow and outflow, lake surface level, and
climate parameters is necessary to determine the water budget for the
lake. Understanding the
water budget is critical for predicting the effects of degassing on
surface water quality and for evaluating remediation plans for the weak
natural dam (spillway) that holds back the upper 40 m of the lake water. VI. Logistics Logistics and organizational arrangements for the day-to-day operation of the camp were undertaken mainly by IRGM with assistance from MINMEE. A.
Transportation
Transportation of the participants and equipment to and from Lake Nyos was undertaken mainly by IRGM with assistance from MINMEE. In addition, IRGM hired five trucks to transport equipment to the site. B.
Accommodation
Since the planned base camp was still under construction, participants stayed in tents supplied by MINMEE and IRGM. A dining space was located and covered with a tarp, and this space functioned as a �meeting room� as well. There was a formal meeting about the day�s events, successes, and problems every evening after dinner. C.
Food
and drinks
IRGM supplied food and drinks as well as all kitchen utensils, with some assistance from the other groups. D.
Electricity
Electrical power required to support most of the mechanical work, computers, and cooking was provided by several gasoline generators supplied by various parts of the project. At the end of the operation a powerful generator (30 KVA) was installed. E.
Boats
Four rubber boats equipped with engines, three from IRGM and one from MINMEE, were used in the operation. At the end of the operation a powerful engine (40 HP) supplied by IRGM was introduced to tow the pipe system to the target locality in the lake. Gasoline for the boats and engines was provided by IRGM. VII.
Future Operations There are three main issues regarding the future operation of the degassing system which are critical to address. The first issue concerns the maintenance and logistics of operating the pipe system and CO2 stations, the second issue concerns the analysis of data produced by the system, and the third issue concerns the continued monitoring of the conditions in the lake. (1) There must be a rapid transition of the maintenance of the pipe system from foreign to Cameroonian engineers. This requires Government support of the training of Cameroonians in France, and in association with French engineers. In addition the base camp at Nyos must be completed to support the presence of Cameroonian technicians in the field. The early warning gas detection systems installed at both lakes also require maintenance; Cameroonian scientists have been trained for this maintenance, but they will require logistical support to travel to the field and work on the stations. (2) The degassing system produces a large amount of data that are transmitted via satellite. Those data must be processed and analyzed to determine if the pipe is operating correctly. Once analyzed, these data are used to make decisions about continued operation of the pipe. For example, if the automatically controlled system determines that the conditions in the pipe such as the rate of flow have deviated significantly from normal operating conditions, the fountain will be reduced to a low flow. At this point a decision must be made on how to proceed, and whether the system should be shut off or whether the large fountain should be restarted. For the coming year (January-December 2001), Data Environment in France will be responsible for processing the data, supported by the OFDA grant. However, this is the final year of the OFDA grant and beginning in January 2002 it will be necessary for the Government of Cameroon to assume the responsibility of data processing. In addition, there is the responsibility of making a decision on how to proceed if there are deviations from the normal operation of the pipe. Beginning in February 2001 the NMDP Advisory Committee will function to advise the Cameroonian Government on what course of action to take if the pipe malfunctions. The NMDP Committee will always be available to act in an advisory capacity, but the responsibility of analyzing the data and making a decision on the course of action ultimately must be transferred to the Government of Cameroon. We suggest that a plan for appropriate training of personnel begin immediately so that this responsibility can be assumed by the beginning of the year 2002. (3) The third major aspect of the future operation of the degassing program concerns monitoring of the lake for changes caused by the degassing. Such changes are important because they may signal difficulties with the degassing procedure. Some monitoring by Cameroonian scientists has already begun, but continued training of students and scientists is required. In addition to the above three issues, the future operation of the overall degassing program also involves the issue of the weak natural dam at Lake Nyos. Further studies on the stability of the Lake Nyos dam are essential to evaluate the next step in mitigation of this additional natural hazard. A small amount of geological data was collected during the present operation, and a more extensive study was performed in March 2001 to evaluate the weakness of the dam and the alternative solutions to stabilize the dam. VIII.
Conclusions
(1) The initial degassing phase of NMDP began at Lake Nyos in January 2001. An automatically and remotely controlled degassing system was installed, and is now functioning on a permanent basis. With this system fully functional, further increase of the CO2 content in the lake will be stopped, resulting in reduction of risk of another gas explosion. However, the rate of gas removal by a single pipe is not sufficient to reduce the CO2 content in the lake to a safe level within a reasonable time span of 5-10 years. Therefore additional funding is needed to increase the number of the degassing pipes to accomplish this goal of making the lake safe.
(2) An early warning gas detection system was set up at both Lakes Nyos and Monoun. The systems monitor the CO2 concentration in the atmosphere continuously and will sound an alarm when a dangerously high CO2 concentration is detected. These systems contribute to the reduction of risk to the population from future gas releases. Detailed physical, chemical, biological, and hydrological parameters of Lake Nyos were collected in order to understand the baseline of pre-degassing conditions in the lake. These data sets will be used for comparison with the future evolution of the lake as degassing proceeds.
(3) Construction of the base camp (observatory and related facilities) is going on by the lake. These facilities will support the maintenance of the degassing operation and the installation of additional pipes in the lake in the future.
(4) The degassing system and early warning systems described above require regular maintenance and data analysis for continued operation. Training of Cameroonian scientists and engineers, management and maintenance of the lake-side observatory and related facilities, and education of local populations about the degassing program are critical for the long-term success of this project. See the FINAL REPORT of the NMDP Project
Acknowledgements We acknowledge with thanks visits of encouragement from the following during the operation: local authorities and population, the 62nd Army Battalion based at Nkambe, the USAID regional African Director for the Environment and the pupils and teachers of Government Primary School Buabua.
List of Participants National participantsMINMEE Paul Ntep Gweth, George Keben Forgwei, Melloh Pius, Djoulde Marcel, Oscar Matip MINAT Henri Enoumba, Celestin Mandeng, Chauffeur MINREST Georges Mbarga, Hubert Mvogo, Francois Zegue Ngatta, Paul Nia, Gaspard Ayissi, Raphael Abega, Jacob Nwalal, Fetus Aka, Luc Sigha, Gregory Tanyileke, Joseph Nnange, Vincent Ngako, Emmanuel Ndinge Zega Theophile, Djelle Molly, Nkem Take Emmanuel, Dominique Bengono Joseph Victor Hell, Ateba Mamoun, Harman Oumarou, Daniel Sighomnou Anong Anong, Michel X (Cabinet MINREST) Cooks Yosah Marcus (Edimo), Peter Modim Labor (Over 80 local people) International participantsFrance Michel Halbwachs, Gerard Vitter, Philippe Blocaille, Alain Felix, Jean-Claude Tochon, Jean-Christophe Sabroux, Patrick Richon, Arne Hodalic, Gaston Kaser Japan Minoru Kusakabe, Yutaka Yoshida USA
Bill Evans, George Kling, Karen Riseng
Last
Updated: June 2001
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