Turbulent dissipation in a near-field river plume: A comparison of control volume and microstructure observations with a numerical model

[1] Data collected from the near-field region (first several kilometers) of the Merrimack River plume are analyzed to provide estimates of turbulent kinetic energy (TKE) dissipation rates. Measurement techniques included a control volume method incorporating density and velocity survey data, and direct dissipation rate measurements by turbulence sensors mounted on an autonomous underwater vehicle (AUV). These two distinct observational approaches are compared with TKE dissipation rates derived from a highly resolved three-dimensional numerical model. In general, there is good agreement between the three estimates of dissipation rate. Differences occurred in two regions: (1) at the base of the plume, where plume density increased, and (2) in the very near field of the plume, which is characterized by rapid acceleration and strong shoaling. Results suggest that there is a feedback between the turbulence and the plume evolution with the result that the spreading rate of the plume is constrained. A scaling parameterization, relating turbulent dissipation rate to plume density and velocity, is also examined. Immediately seaward of the front this parameterization appears to be consistent with observed rates of dissipation, but progressing seaward, a modification to the parameterization may be necessary to account for plume spreading and deepening.