Numerical simulations of degassing scenarios for CO 2 ‐rich Lake Nyos, Cameroon

A catastrophic outgassing of carbon dioxide (CO 2 ) from Lake Nyos, Cameroon, occurred in 1986. Concentrations of dissolved CO 2 have been increasing in the bottom waters since 1986, prompting an international effort to engineer controlled degassing that would maintain lake stability by reducing the gas concentration. A new model, based on the one‐dimensional Dynamic Reservoir Simulation Model has been used to simulate the evolution and distribution of CO 2 in Lake Nyos. Initial conditions for the simulations are taken from published observations and integrated forward with synthesized, daily meteorological data for 5 years. After model results were found to be in agreement with observed trends, a hypolimnetic piped withdrawal system for degassing the lake was then modeled to simulate its effect on the CO 2 concentration profile over time. In the standard degassing operation, gas‐rich bottom water continuously flows up through pipes, discharging as a fountain at the lake surface. Simulation results indicate that the lake density structure will most likely remain stable and CO 2 concentrations will decrease at all depths above the pipe intake. Seven alternative operational strategies for the degassing system were also investigated, including a submerged outlet, an intake raised above the lake bottom, higher flow rate, a disrupted operation schedule, employment of a stabilization pond, multiple intake depths, and release of the withdrawn water from the lake. Multiple intake depths best maintain lake stability. A tentative conclusion is that degassing may need to be carried out indefinitely, albeit intermittently or at a reduced flow rate.