Safeguards from #drought and barges on the #MississippiRiver – NOAA
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Mississippi River water levels normally decline in fall and winter, but not as much as October 2022. Lack of rain in the Ohio River Valley and Upper Mississippi Valley over the past few weeks has caused River water at levels not seen in over a decade along key parts of the river. Low water levels are slowing barge traffic and raising concerns that saltwater intrusions in the lower Mississippi could affect water supplies.
The Operational Earth Imager (OLI-2) on Landsat 9 captured this natural color image of the parched river on October 7, 2022. The image shows backed up barges north of Vicksburg, Mississippi. At times, well over 100 tugs and barges waited due to a temporary river closure caused by barge groundings and dredging, according to dispatches. Tugs and barges are grouped into groups of varying sizes, but can easily be 300 meters long and 30 meters wide.
The map above shows how wet the ground was on the same day the Landsat 8 image was acquired. Using data from the Crop Condition and Soil Moisture Analytics (Crop-CASMA) product, the map shows soil moisture anomalies on October 7, 2022, or how the water content in the top meter (3 feet) of the ground relative to normal conditions for the time of year. The brown areas were drier; the blue areas were wetter. Crop-CASMA integrates measurements from NASA’s Soil Moisture Active Passive (SMAP) satellite and vegetation indices from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA’s Terra and Aqua satellites.
The river level at Vicksburg had dropped to 0.66 feet (0.20 meters) on October 20, a low level but still well above the record level of −7.00 feet in 1940. However, further upstream in Memphis, the river level dropped to -10.79 feet on October 17, 2022, the lowest level recorded at the site since National Weather Service records began in 1954.
In New Madrid, Missouri, water levels had dropped to -5.1 feet on Oct. 20, just slightly above the gauge’s minimum operating level. Water levels, or “gauge height” or “river levels” do not indicate the depth of a stream; rather, they are measured against a chosen reference point. This is why some gauge height measurements are negative.
A lack of rain over a very wide area is the main reason water levels have dropped so low, said Tennessee state climatologist Andrew Joyner. “It doesn’t take long for the water levels to drop given the lack of rain over such a large area,” he said.
Downstream in the lower part of the river, the U.S. Army Corps of Engineers deal with salt water intrusion in the lower reaches of the river. Normally, the river’s flow prevents salt water from the Gulf of Mexico from coming very far upstream, but the river is so low that a wedge of salt water has crept north and is threatening catches used for fresh water supply. To prevent salt water from rising further upstream, the Corps began construction of an underwater sill at Myrtle Grove, Louisiana on October 11.
The forecasts of the National Weather Service Lower Mississippi Forecast Center calls for water levels to drop even further at several points along the river in the coming weeks. In many cases, they expect water levels to drop even lower than they did in 2012, 2000 and 1988, other years when water levels hit lows. abnormally low.
What will happen beyond a few weeks is less clear. “Looking at the one- and three-month forecasts, it looks like there’s an equal chance of above-average or below-average rainfall,” Joyner said. “If we end up with average rainfall, conditions may not worsen, but it won’t lead to improvements either.”
NASA Earth Observatory images by Joshua Stevens, using soil moisture data from Crop Condition and Soil Moisture Analytics (Crop-CASMA), Landsat data from the US Geological Survey, and data from the National Water Information System. Story of Adam Voiland.