DOI: 10.17882/74747
title: Hydrographic data from near-field Doubtful Sound, New Zealand

description: Here we provide hydrographic data from the near-field region, Deep Cove, in Doubtful Sound, New Zealand. A controlled freshwater discharge is carried from alpine lakes (Manapouri and Te Anau) through the Manapouri hydroelectric power station and, via a constructed channel, into the head of Doubtful Sound, located on the southwest coast of New Zealand (45.3 S, 167 E). The freshwater tailrace is discharged into the head of the inner fjord, Deep Cove. Deep Cove is 3.6 km long and, flanked by steep topography, has a maximum depth of 126m that occurs within 50m of the shoreline. A 2-week field campaign was conducted in March 2016. A vessel-based survey was conducted to obtain a highly-resolved spatial distribution of density, velocity and turbulence fields within Deep Cove. Along-channel and across-channel vessel transects, aligned with, and perpendicular to, the main river discharge, respectively, were repeated over the course of the field campaign. The along-channel transects represented the path of the mean flow as the vessel drifted with the seawards-propagating plume. A weighted bow chain attached to the vessel was comprised of continuously sampling temperature (RBRsolo) and CTD loggers (RBRconcerto), spaced 0.5m apart and sampled at 2 and 5 Hz respectively. High-resolution profiles of practical salinity and temperature were obtained from “tow-yoed” CTD loggers (RBRconcerto), sampling at 5 Hz. The tow-yoed CTD was continuously profiled with a fall rate of approximately 1m/s. A microstructure profiler (VMP 250, Rockland Scientific) was deployed from the side of the vessel, measuring small scale velocity shear from which estimates of TKE dissipation rates were directly obtained. The VMP was deployed in an upwards-profiling mode which enabled measurements right to the water surface. Further details about the calculation of dissipation rates from velocity shear and other details pertaining to the microstructure data set are thoroughly discussed in Appendix A of McPherson, R. A., Stevens, C. L., & O'Callaghan, J. (2019). Turbulent scales observed in a river plume entering a fjord. Journal of Geophysical Research: Oceans, 124, 9190 - 9208, https://doi.org/10.1029/2019JC015448. Horizontal velocity estimates were obtained from a 600 kHz ADCP (RDI Workhorse) mounted on a pole along-side the vessel 1m below the surface, set to sample water velocity continuously in 1m vertical bins. A 600 kHz narrow-beam echosounder (EK60) was also mounted on the other side of the vessel to provide a means of imaging the flow on fine horizontal and vertical scales. A 600 kHz echosounder (EK60) was positioned 0.5m below the water surface and measured backscatter in 4.5 cm bins down to 38.5m. Precision position data were obtained from an onboard GPS unit. A schematic of vessel-mounted instrumentation setup including bow chain, pole-mounted ADCP and EK60, tow-yoed CTD and microstructure profiler, as well as further details, are found in: McPherson, R. A., Stevens, C. L., O'Callaghan, J. M., Lucas, A. J., and Nash, J. D.: The role of turbulence and internal waves in the structure and evolution of a near-field river plume, Ocean Sci. Discuss., https://doi.org/10.5194/os-2019-120, in review, 2019.