Recent articles in some New Orleans news sources have questioned the role of deepening the Mississippi River shipping channel in the intrusion of the saltwater wedge upriver. The stories note that no objections related to saltwater intrusion were raised in the few hundred public comments on the deepening and acknowledge that the Corps of Engineers was well aware of the issue. The Corps concluded that it was an issue the parishes could deal with.
The New Orleans Engineer District says on its website, “Since the Mississippi River is a source for municipal and industrial water supply, the effects of increasing the navigation channel depth from 45 feet to 50 feet were carefully analyzed in the studies for the deeper channel.” Deepening planners were also aware of the effects of climate change, which have been part of Corps studies and planning for years now. This year’s extended drought in almost the entire river basin has reduced flows to the point that the saltwater wedge crept higher upriver than in recent memory.
River flow is the single most important determinant of when and whether salt water will intrude upriver. However, a lot of things affect river flow besides drought, climate change or channel deepening. There are also more than a dozen freshwater diversions in the Lower Mississippi River. Their purposes are either to build up wetlands or marshlands with silt or to increase freshwater flows to certain areas.
The Mississippi River provides drinking water for millions. It also supports a $12.6 billion shipping industry, with 35,300 related jobs. It’s a source of irrigation water for farmers, a fish and wildlife habitat and a drainage basin. Some advocates want more flood control; others want to restore the wetlands that used to exist alongside the river, many of which were filled in to create cities and towns.
The Father of Waters has a lot of clamoring children asking for different things. During last year’s drought in the West that diminished the Colorado River, there were even revived calls to pump Mississippi River water out west, a literal pipe dream that’s more than a hundred years old.
Saltwater intrusion is an issue that may become more frequent as the climate changes. But as an article in this week’s issue notes, it has already happened far more often than most people were aware at the time. The farthest north the salt water traveled on record was all the way to Mile 119 in 1939 and 1940—long before channel deepening at the river’s mouth.