Model investigations of discharge plumes generated by deep-sea nodule mining operations

Deep-sea nodule mining operations potentially involve plans for discharge plumes to be released into the water column by surface operation vessels. As such, we consider the effects of non-uniform, realistic stratifications with vertical shear on forced compressible plumes for application to nodule mining applications. The plume model is developed to account for the influence of thermal conduction through the discharge pipe and an initial adjustment phase. We investigate and elucidate the substantial role of compressibility, for which a dimensionless number is introduced to determine its importance compared to that of the background stratification. Our results show that (i) small-scale stratification features can have a significant impact, (ii) in a static ambient there is a discharge flow rate that minimizes the plume vertical extent, (iii) the ambient velocity profile plays an important role in determining final plume scale and dilution factor, and (iv) for a typical plume the dilution factor is expected to be several hundred to a thousand.