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Sensors and Superstorm Sandy

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Issue: 
Fall 2012

John Porter (VCR)

As this issue of Databits was about to go to press, "superstorm" Sandy had a near-miss on the Virginia Coast Reserve. It provided an excellent opportunity to see how sensors perform under heavy-duty conditions. Generally speaking our sensors worked well throughout the storm, and it appears that all of them on Hog Island (our principal barrier island research site) survived and collected interesting data throughout the storm.

This is not to say that Murphy's Law didn't come into play as well. Our main radio hub on the north end of Hog Island developed a power glitch, probably related to a dodgy power inverter, two days prior to the arrival of Sandy that caused it to come up for about 1 minute, transfer lots of data, then go off the air again for the day. This was annoying in that it prevented us from dumping the data from the island real-time, but even the brief transfer window was enough to get back some interesting results. Also in accordance with Murphy's Law, now that the storm has past, the radio hub is working perfectly!

New Tide Station. Radar sensor and data logger are in the black box under the solar panel. Radio communications are via a 900MHz directional antenna on the mast.

Our biggest suspense was over a new radar tide station installed on an abandoned navigational marker only days prior to Sandy's arrival. The box containing the sensor and logger are suspended about 3 meters above the water, but we feared that a major storm like Sandy could produce a large storm surge that might just be high enough to wash the box away! Fortunately, as seen in the graph below, the water level only rose to within 1.2 meters of the box so we got a good first-hand view of the storm surge related to Sandy. Especially notable is how quickly the storm surge abated as Sandy passed. Tides returned to normal ranges over the course of a single tidal cycle, dropping over 2 meters between high and low tide (normal tidal range is about 1.3 m), after building up for several days as Sandy approached.

Tides off Hog Island during "superstorm" Sandy

Another source of suspense was our network of ground water wells. These wells are located in rough lines across Hog Island, and although all the electronics are located well above ground, the exceptional tidal flooding still placed them at risk. Fortunately, none of the data loggers appear to have been submerged, although one located by a pond probably came pretty close as water levels "spiked" around the time of peak flooding from Sandy. Note on graph below, the spike represents standing water around the well - and the quick decline occurred as water flowed away above-ground. The slower decline on the "shoulder" of the curve represent the slower flows out of the well through the sand.

Well near pond in central Hog Island

Sandy also provided an excellent opportunity to test out some of the newer sensors we have deployed. One is an "impact" rain gauge that uses the impact force of rain drops onto a piezoelectric sensor to model the rain amounts. We are hoping to replace many of our (frequently clogged) tipping bucket rain gauges with this technology. The Morella cerifera seeds that abound on our site are exactly the right size to get through the mesh on a tipping bucket rain gauge, but just big enough to clog up the drain! However, the flat plate of the impact gauge can't be clogged. To test the impact gauge, our newest station on Hog Island includes both tipping bucket and impact gauges. During Hurricane Irene, the bucket blew out of the tipping bucket gauge, so we weren't able to do a comparison. However, during Sandy both gauges stayed operational and the correspondence between sensors was excellent. In the graph below, the red line indicates the tipping bucket rain gauge and the blue the impact gauge.

Rain gauge comparison

Finally, no discussion of sensors at the Virginia Coast Reserve LTER would be complete without mentioning the webcams. Again, Murphy's Law kicked in with our Broadwater Camera experiencing a power problem (again, probably a bad inverter) that caused it to communicate much more slowly than usual, with "ping" times of over 1 second. Nonetheless the camera was able to capture an array of photos during the storm. Many of them were less than optimal because the high winds caused the camera to shake, but they still provide a graphic record of the extent of flooding during "superstorm" Sandy. Below are pictures of South Hog captured during peak flooding and after flooding subsided. The dark areas are the Morella shrubs that stuck up out of the water. Also there is a picture of a very wet Peregrine Falcon that rode out the storm, with its mate, in the Cobb Island hacking tower. Additional photos are available at: http://amazon.evsc.virginia.edu/gallery23/main.php/v/events/Sandy2012/

Peak Flooding on South Hog

Post Flooding on South Hog

Peregrine Falcon, during Sandy