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Jet Ski Provides Platform for Collecting Water Quality Data in Bay Studies

By Steve Werblow
Freelance Journalist
Ashland, Oregon

Bret Webb
Assistant Professor
University of South Alabama
Mobile, Alabama

Lightweight, portable and with minimal draft, the Jag Ski collects high-resolution data, georeferenced with real-time, kinematic GPS, across the deep shipping channel and the broad shallows of Mobile Bay.

Jet skis are no longer just for fun; they can also be platforms of opportunity for coastal research. The Jag Ski, a red-and-white Kawasaki Ultra LX personal watercraft (PWC) designed by the University of South Alabama's Bret Webb, isn't built just for thrill-seeking, but for bathymetric surveying, multiparameter water quality sampling and water-velocity studies in the shallow estuarine environment of Alabama's Mobile Bay.

Mobile Bay, roughly 48 kilometers by 19 kilometers wide, is a drowned river mouth estuary that receives an average freshwater discharge of 1,800 cubic meters per second from several rivers, including the Mobile and Tensaw. The bay's average depth is 3 to 4 meters, sliced through by a 12-meter-deep shipping channel.

When the Deepwater Horizon oil platform exploded and sank about 161,000 meters off the mouth of Mobile Bay in April 2010, the Jag Ski was used to study the movement of oil from the spill. The findings revealed the dynamics of the Mobile Bay estuary and the performance of structures designed to repair the barrier island at the mouth of the bay.

Jag Ski Equipment
The Jag Ski was initially designed to study scour holes near bridge foundations and study nearshore currents, as its size and maneuverability allow it to access study sites unreachable by most boats. It was then equipped to carry out bathymetric surveys in shallow areas and the surf zone.

The PWC uses a River'Surveyor M9, an acoustic Doppler profiler (ADP) manufactured by SonTek (San Diego, California). The RiverSurveyor M9, designed to deliver velocity and direction measurements from 6 centimeters to 40 meters depth, is also equipped with real-time kinematic GPS.

The dynamics of river discharge and tides from the Gulf of Mexico result in a wide range of salinity in Mobile Bay. Salinity, measured in practical salinity units from 0 for pure freshwater to 42 for highly saline ocean water, is often as low as 5 practical salinity units, but, in drought conditions, the salt wedge pushes well north of the bay into the delta and rivers, raising salinity. During the same survey, it would not be uncommon to have salinities ranging from 5 to 30 practical salinity units, which is near oceanic salinity. Accounting for salinity and temperature in coastal surveys is important because those variables affect the speed of sound and, therefore, ADP data.

The Jag Ski is also equipped with a SonTek CastAway CTD. At every kilometer or so, the instrument is cast to steadily freefall with a sampling rate of five samples per second. Data from the CastAway integrates with the ADP's RiverSurveyor Live software package, generating sound-speed corrections for the acoustic data. The software yields real-time water velocity, direction and estimates of discharge, and allows information to be viewed in multiple data sets simultaneously during surveys on the waterproof computer aboard the Jag Ski or back on shore. The program integrates GPS, CTD and ADP data, and exports to MathWorks Inc.'s MATLAB or Hypack Inc.'s (Middletown, Connecticut) HYPACK software. To continue this article please click here.

Steve Werblow is a freelance writer based in Ashland, Oregon. He covers agriculture, resource industries and water issues. Examples of his published work can be found in
Everything About Water, Industrial Environmental Technology, Brisbane Times, Australian Geographic, Process and Control Engineering, Hydraulics and Pneumatics, Industrial Water World, Marine Scientist and more.

Bret M. Webb is an assistant professor of civil engineering at the University of South Alabama, as well as a practicing engineer at South Coast Engineers LLC. His research interests include coastal and estuarine hydrodynamics, tidal processes, sediment transport and coastal mod

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