The storm left behind massive new patches of open water that scientists can be watching carefully to see if vegetation and wholesome marshes return.
Hurricane Ida might have moved on, however the internet of issues the highly effective hurricane left behind after striking southern Louisiana stay. In lots of of the hardest-hit communities, entry to energy, air con, and gasoline stays a problem. Large numbers of houses have been destroyed or severely broken. Some key roads and bridges are out, and returning residents are dealing with curfews and boil water warnings.
5 days after catastrophic storm surge, winds, and downpours pummeled the Mississippi River Delta, Landsat 8 acquired imagery of the storm-damaged area. The false-color pictures above present a portion of far southern Louisiana, together with the Barataria Basin and Breton Sound, on September 19, 2015 (left) and September 3, 2021 (proper). Whereas Landsat 8 collects new imagery of this space each two weeks, newer pictures from 2016-2020 had vital cloud cowl.
The picture combines purple, near-infrared, and short-wave infrared wavelengths (bands 5-4-3) to make it simpler to tell apart between water (darkish blue) and vegetation (inexperienced). Water with extra suspended sediment seems lighter blue. The suspended sediment appears to be like brown in the natural-color model of the identical picture (beneath).
5 days after the storm, many water our bodies had been nonetheless discolored by sediment stirred up by rain and floods. Floodwaters nonetheless swamped areas alongside many rivers, coasts, and lakes. Broken or lacking marsh vegetation left massive patches of open water, particularly in components of the Lafourche, Jefferson, and Plaquemines parishes. The picture beneath exhibits a extra detailed view of an space in Lafourche Parish close to Larosa. The big rectangular function is a low-lying farm constructed on reclaimed land and guarded by a levee and pumping system. (Verify Worldview to see a cloudier pair of images that present marshes in this space earlier than Ida hit in August 2021 in comparison with after the storm in September 2021.)
“A mixture of flooding, erosion, and defoliation throughout Ida doubtless created many of the brand new patches of open water seen in the Landsat picture,” defined Marc Simard, the principal investigator for NASA’s Delta-X mission, a subject marketing campaign to the Mississippi River Delta that was conducting analysis on sediment and marsh dynamics when Ida approached. After canceling some subject work whereas Ida was close by, the Delta-X staff restarted flights a couple of days later and has been utilizing plane-based radar, together with the UAVSAR and AirSWOT sensors, to evaluate the results of the storm. In mid-September, when waters have receded some, flights carrying the AVIRIS-NG sensor will even resume. Information assortment groups will even return to the sphere and to boats to start sampling from the bottom once more in mid-September.
“One of the fascinating issues to look at can be to see if the stark modifications you see in this Landsat picture show to be momentary or lengthy lasting,” mentioned Simard. “Some of the losses might have been floating vegetation that washed away or vegetation that merely misplaced their seasonal leaves and can most likely develop again. Different had been uprooted and can not supply the coastal safety they as soon as did.”
Among the many issues that Delta-X groups can be monitoring carefully is how salinity ranges and the quantity of sediment in water shifts in the area over time. “If the salinity gradients have modified as a result of of Ida and salinity will increase inland, it can kill off freshwater marshes, and they are going to be changed by salt marshes,” mentioned Simard. The staff will even be watching how a lot sediment is coming in from rivers and obtainable to replenish eroded coastal areas or backside sediments that had been displaced through the storm. As an illustration, small topographic options in the underside sediments decide whether or not vegetation can thrive.
“I believe we’ll see that wholesome wetlands with a lot of incoming sediment can be much more resilient than wetlands which obtain little no sediment from river discharge,” mentioned Simard. “Our hope is that the fashions being developed by Delta-X scientists will present a practical perception into the vulnerability and resilience of wetlands in this area in the long-term.”
Previous to the storm, the wetlands in this space were losing land at one of the quickest charges in the world because of the mixed results of upstream dams and levees that lure or divert sediment, subsidence of the land, and rising sea ranges. Subsidence, or sinking of the land, is attributable to pure settling and compaction of new delta sediment and by human actions, akin to pumping for groundwater or oil.
NASA Earth Observatory pictures by Joshua Stevens, utilizing Landsat knowledge from the U.S. Geological Survey.