Acoustic Doppler Current Profiler System at UTMSI Pier (Part 1)

The currents at the UTMSI pier near the mouth of the Aransas Pass inlet toward the Gulf of Mexico is quite dynamic. Since the Aransas Pass inlet is one of the major channels in the South Texas coast for water exchanges between the Gulf of Mexico and the local bays, better understanding of characteristics of the currents and tides are important not only for science but also for fisheries and transportation. The currents and tides at the UTMSI pier have been observed by Tony Amos’ pioneering efforts during the last 2-3 decades in this location. Although the daily tidal amplitude is barely a foot range, this is by no means
insignificant considering the shallow bays in the region (1-3 m depth) except for the dredged parts. The currents at the inlet is mostly bimodal due to tidal currents and elongated channel axis, and its speed often exceeds 2 knots and occasionally
exceeds 3 knots. Except for few occasions of time-series current meter measurement by the Texas Water Development Board and few research surveys during the past several decades, most current observations at the pier have been limited at the fixed depths (e.g. at 1m from surface and/or 1 m above the bottom). The “side-looker” current meter installed at 7 m depth at the pier by the Texas A&M – Corpus Christi group only looks at the 7 m water depth as well.

The main objective of my efforts in deploying another current meter at the pier is to investigate the current characteristics for the whole water column and build the time-series data. This information would be useful in better answering basic
questions such as “How significant is the vertical velocity shear?”, “How the vertical velocity distribution changes along the tidal cycle?”, “How significant is the upwelling/downwelling – vertical – velocity?”, “Would there by any net zero
velocity plane in the water column over tidal cycles?”, and “How much turbulent is the water column?”.

I acquired a Nortek Aquadopp current profiler (1 MHz) with an asymmetrical transducer heads that can be mounted to monitor the 12 m water column. The 30 m cable connected between the profiler and the lab computer not only allows the real-time data monitoring but also supplies the power to the profiler. So, the internal memory and battery inside the
profiler are used as backup. The current deployment design is that the profiler is installed on the bracket at about 1 m water depth looking down toward the bottom. The 21 beam cells are assigned with 0.5 m thickness interval and with 0.4 m blanking distance. The currents are recorded at every 10 minutes with 1 minute averaging. The basic wave
parameters are also recorded every hour.

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