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A project log for Oceanography for Everyone: The OpenCTD

Empowering researchers, educators, and citizen scientists through low-cost, open-source hardware.

andrew.david.thalerandrew.david.thaler 09/06/2016 at 18:460 Comments

We deployed two OpenCTDs in a tidal estuary ahead of Hurricane Hermine.

Background

Hurricane Hermine is a tropical cyclone that passed over our field site in coastal Virginia on September 4, 2016. To test the longevity of the batteries and the durability of the OpenCTD during long term deployments, I placed two units in our Test Ditch (a tidally influence drainage ditch connected to the Mobjack Bay estuary that is conveniently located on our property), where they remained for 74 hours.

Photo Narrative

Photo of deployment siteDeployment site.

Photo of deployment site at peak floodDeployment site at time of peak flooding.

Photo of wider flood zoneWider flood zone to show extent of flooding.

Photo of deployment site at recoveryDeployment site at time of recovery.

First look at the data

Hermine deployment for CTD 2This is the cleaned data from the second unit, which used a cheaper conductivity probe. It was deployed at dead low tide 12 hours before Hermine was supposed to hit.

Temperature: Temperature is relatively stable and declines predicatably as air temperature declined during the storm, and then rose once the storm passed near the end of the deployment. Two rapid drops can been seen in the first 24 hours of deployment, these correspond to heavy rainfall.

Salinity: Salinity climbs rapidly as Hermine drives salty seawater up into the Chesapeake and then Mobjack Bay. It declines slightly in conjunction with the heaviest rainfall, and then rises. It fluctuates slightly with changes in sea level, but remains high throughout the deployment.

Depth: This is a lot of flooding for the region. Low tide during the storm is almost as high as pre-flood high tide. Because this is a drainage ditch, tides don't fall like they normally would, since runoff continuously adds more water during the storm, leading to low-tide spikes rather than gradual curves as seen druing the first and last low tide.

As important as sensor validation against other equipment, these readings are consistent with observed environmental conditions during the time of deployment.

Notes

One salinity probe appears to have lost calibration (mid-level graphite probe), furthur investigation will determine if the data is recoverable. This particular unit has been used for several dozen test deployments and has been pretty beaten up. It is likely that conductivity calibrations will need to be conducted more often than originally anticipated.

Lessons Learned

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