Public Lab Research note

Quick Kite Survey of Bayou St John Wetland, post-Cindy, July 1st 2017

by eustatic | July 10, 2017 21:38 10 Jul 21:38 | #14643 | #14643

Miriam and I wanted to see how quickly we could survey the Bayou St John wetland.

It's been a while since my last survey flights, where I was trying to elaborate and test on the issue of usability of drones vs kites for surveying, and surveying this site. Since then, one of my drone students crashed and destroyed one of the propellers, and I haven't had time to fix it.

Similarly, many of my old kites are in disrepair, but we spent about 15 minutes making a new cross-spar for my 9' Delta kite. Wind was too low for a flowform kite, but the Delta flew straight up, with about ~1 kg of force in uneven, ~10 mph winds, on the second attempt.

We wanted to put a camera up quickly, so we used a RGB mobius camera with a plastic soda bottle rig (~0.2 kg) , mounted to a Delta kite. There's some video of this [placeholder for video link]

Here's the weather on July 1st, we waited until the afternoon, when winds were likely to be high enough, and tides would be falling. Hurricane Cindy had recently raised water heights on the south shore of Lake Pontchartrain by three to four feet. (Seabrook gauge, USGS)image description

The water was a bit high, but within a normal tide range.

What we were able to capture was the movement of a Shell bar west, up out of the water entirely. This shows up as a white line just east of the concrete pad of the levee. This Shell bar was not moved as far as the wrack line, a brown line that was also moved by Cindy's high water.

image description

We've been documenting the movement of these Rangia shells ever since tropical Storm Karen pushed them into the Bayou from under the overpass, where the dredging contractor had placed them. [Click here for the gif] The shell bar has moved over the eastern side (channel side, the deeper side)) of the planted wetland, smothering, but not entirely wiping out planted Spartina and Scirpus reeds. Andy Baker for LPBF had been using previous photos to manage the site. In 2017, LPBF and other orgs are no longer funded to maintain the site, although other groups and the Levee board, i believe. have stepped up to remove trash.

Other things of note: we were able to document recreational use of the site by taking pictures of a number of cars parked on st bernard ave, as well as number of tents and number of people-shaped blobs in the water next to the tents. .image description

There are 11 cars, two pop up tents, and 16 people swimming at the mouth of the bayou. Note the new seawall armoring on the upper left. At the bottom of the photo, we can compare the relatively plant-less west side with the flourishing marshes on the east side. We can also see the darker water that signifies the channel that was dredged to improve water circulation.

Also we note that the channel which was dredged and planted in 2013 seems to have filled in lakeward of the overpass by summer 2017. the RGB picks up this basic color difference. This general observation was confirmed by someone who saw the facebook post of this kite image. LPBF has conducted a post construction bathymetry survey. They could repeat this survey if they wanted to know how much the channel has filled in. I don't know how this affects the oxygen levels in the Bayou south of the overpass. Restoring a channel for migration of fish and replenishment of oxygen levels was the purpose of the re-dredging of this historic bayou, from when a road was placed though it.

In this case, we lucked out, in that Cindy seems to have done some of the work for us, moving shell that may have smothered the planting.

It's also interesting to me that shells move with less water than sand. The sand in the wetland seems to have largely stayed put. But the shells are obviously more dense than the wrack, which is just dead plant materials. How much of this is due to the death of the plant roots that may have otherwise prevented the movement of this material?

It's important to have a low cost, quickly applied method like the kite to monitor sites that have few or no institutional support. It only took about 30 minutes to take the pictures.

Here's a link to the Isee Change post.


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