Study: Low water levels make shipping difficult on Mississippi River and move salty water upstream
In addition to slowing barge traffic, low water levels have raised concerns that saltwater intrusion in the lower Mississippi River could affect water supplies.
Operational Land Imager (OLI-2) on Landsat 9 captured this natural-color image of a depleted river on October 7, 2022 (below). This image shows a barge pouring north of Vicksburg, Mississippi. It was learned that more than 100 tugboats and barges were waiting as the river was temporarily closed due to barge grounding and dredging work. The tugs and barges are strung together and come in a variety of sizes, but can easily be 1,000 feet long and 100 feet wide.
The map above shows how wet the soil was on the same day the Landsat 8 imagery was acquired. Using data from the Crop Condition and Soil Moisture Analysis (Crop-CASMA) product, this map shows soil moisture anomalies on October 7, 2022. Among them, the brown area is relatively dry, and the blue area is relatively wet. Crop-CASMA integrates measurements from NASA’s Soil Moisture Active Passive (SMAP) satellite and vegetation indices from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA’s Terra and Aqua satellites.
By October 20, the river level in Vicksburg had dropped to 0.66 feet, a low level but still well above the record low of -7.00 feet set in 1940. However, on Oct. 17, 2022, further upstream in Memphis, the river’s water level dropped to -10.79 feet, the lowest level since the National Weather Service began keeping records there in 1954.
In New Madrid, Missouri, on Oct. 20, the water level dropped to -5.1 feet, just above the minimum operating level of the water gauge. Water levels do not indicate the depth of rivers, instead they are measured relative to a chosen reference point. This is why some water level gauges have negative height measurements.
Tennessee climatologist Andrew Joyner explained that the lack of rain in a very wide area is the main reason why the water level has dropped so low. “Given the lack of rain on such a large scale, it didn’t take long for the water level to drop,” he said.
Downstream of the river, the U.S. Army Corps of Engineers is dealing with saltwater intrusion down the river. Normally, the flow of river water would prevent saltwater from the Gulf of Mexico from moving far upstream, but the river was so low that a wedge of saltwater had crept northward and threatened intakes for freshwater supplies. To prevent the saltwater from moving further upstream, the U.S. Marine Corps began construction of an underwater strut in Myrtle Grove, Louisiana, on Oct. 11.
Forecasts from the National Weather Service’s Lower Mississippi River Prediction Center point to lower water levels at several points along the river in the coming weeks. In many cases, they expect water levels to be lower than in 2012, 2000 and 1988 — other years when water levels reached unusually low levels.
What will happen in a few weeks is less clear. Joyner said: “Looking at the one-month and three-month forecasts, it looks like the chance of above or below average rainfall is equal. If we end up with average rainfall, the situation may not get worse, but it won’t cause improve.”