Sensitivity Analysis of Diffusion Coefficient in Water Environmental Capacity Calculation
- Shasha Lu (Second Institute of Oceanography) | Xiaoming Xia (Second Institute of Oceanography)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- diffusion coefficient, theoretical solution, contaminant transport, environmental capacity, numerical solution, Sensitivity analysis
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Water environmental capacity is a popular approach for governments to prevent water pollution. Diffusion process is important in contaminant transport. The contaminant concentration in non-flow/unidirectionalflow water was solved by theoretical solution, while that in an actual sea was solved by numerical solution. The results were compared with different diffusion coefficients, showing that the difference in the calculated environmental capacity approximately equals the ratio of the different diffusion coefficients, which can be increased to multiple times. However, the difference of multiple times is too significant for the environmental capacity. Therefore, it is necessary to add parameter sensitivity analysis and calibration before the calculation of water environmental capacity.
In 1986, the Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP) defined environmental capacity as: Environmental Capacity is a property of the environment and can be defined as its ability to accommodate a particular activity or rate of activity (e.g. volume of discharge per unit time, quantity of dredging dumped per unit time, quantity of minerals extracted per unit time) without unacceptable impact (GESAMP, 1986). Environmental capacity is similar to the concept of Total Maximum Daily Loads (TMDL) and assimilative capacity (Cairns, 1977), which is a very important concept in water pollution control, providing a basis for governments to set pollutant discharge standards (Yang et al., 2015; Liang et al., 2015).
The calculation of the environmental capacity depends on contaminant transport (Gang et al., 2014). When a contaminant is discharged into the water, which is referred to as mixing water, instead of stratified water, it migrates mainly through advection and diffusion processes, while being transferred due to chemical and biological effects. The diffusion process is mainly controlled by the diffusion coefficient. The accuracy of the diffusion coefficient is an important precondition for accurately predicting the contaminant transport and environmental capacity. There are many empirical formulas to calculate the diffusion coefficient at present (Elder, 1959; Holley et al., 1972; Fischer, 1978). Since the applicability of the formula to each water body is different, the parameters of the formula need a calibration test using field data before being used. However, in reality, the value of the parameters including diffusion coefficient lacks field data calibration in China, due to the difficulty in obtaining field measurement (Gu et al., 2014; Wu et al., 2016). Due to this, the value of the diffusion coefficient may not necessarily be accurate, potentially overestimating/underestimating the water environmental capacity. Therefore, a sensitivity analysis of diffusion coefficient in water environmental capacity calculation was carried out in this study.
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