How to destroy a delta: Mississippi vs Nile approaches
by Len Bahr, PhD*
Even casual readers of LaCoastPost typically realize that short-sighted federal and state policy decisions during the past two centuries have rendered the Mississippi River watershed – and especially its delta – highly dysfunctional. The familiar litany of mistakes is topped by a levees-only policy on the part of the Corps of Engineers, which isolated the river from its delta in a successful but misguided attempt to prevent local river flooding.
There is perhaps less recognition that we’re not alone at the mouth of the sinking and shrinking Big Muddy delta, in that deltas are dying all over the globe, threatening more than a billion people who depend on these wonders of nature.
The Mississippi and Nile river systems have much in common, as well as distinct differences. Science Magazine recently published a sobering report on severe crises facing the Nile River delta and its fifty+ million residents. I highly recommend reading this four page article that would be interesting by itself but is particularly instructive for those of us concerned about the increasing morbidity of the Mississippi River delta.
Figure 1 shows satellite views of these two formerly magnificent deltas, at approximately the same scale. These low resolution images hide the cultural changes (such as described in the Science essay for the Nile delta) that are literally wringing the lives from these deltas.
Key differences between the Mississippi and Nile deltas include their respective watersheds and flow volumes. For the ten millennial span of Holocene period since the last ice age the watershed of the Mississippi has primarily occupied temperate deciduous and prairie biomes that comprise the central portion of the US. This vast watershed occupies a climate regime that maintains significant primary production to feed much of the world and sufficient runoff to supply flow to the upper Mississippi, Ohio and Missouri tributary systems.
So far at least, annual rainfall and snowmelt combine to make the lower Mississippi the third most powerful river on Earth, after the Amazon and Yangtze. The growing signs of climate change, including drought/flood events, make future bets very unwise, however.
Forgive a slight digression. Last Friday at the conclusion of the High Water Inspection Trip for the Mississippi River Commission, I had a conversation with Brigadier General Michael Walsh (who is mentioned in an April 23 coastal scutttlebutt minipost). The general has been calling for someone to write a sequel to John Barry’s Rising Tide, looking forward to the end of the century rather than back.
General Walsh apparently wants a credible handbook for sustainably managing the entire Mississippi River watershed and its delta. In considering such a project I believe that, given the pace of change, e.g., energy, freshwater and even phosphate fertilizer, the uncertainties through 2020 are challenging enough, let alone projecting nine decades.
Back to the comparison between the Mississippi and Nile systems, Mississippi outflow provides roughly 90% of the freshwater input to the entire Gulf of Mexico. This flow, coupled with a relatively low population density in south Louisiana, makes the Mississippi delta unique in the US, in terms of landscape having a superabundant source of clean freshwater. Don’t think that our neighbors in Texas aren’t aware of this ‘imbalance.’
In striking contrast with the Mississippi watershed and delta, the Nile supports one of the densest populations in the world. Since the age of the Pharaohs the residents of the Nile River valley, and especially its delta, have been absolutely dependent on river water, which is now running out, as described in the Science report mentioned above.
During the past ten thousand years of the Holocene period the Nile watershed, which consists largely of desert, has delivered far less water to its delta than has the Mississippi. This explains the large difference in delta areas.
In terms of time, it’s truly humbling to realize that some of our more technologically advanced ancestors in the northern part of Africa were using the Nile to transport massive stones to build pyramids two thousand years before the delta land underneath New Orleans even existed!
The population of Egypt grew exponentially during the latter half of the 20th century. In addition to recently expanded use of Nile river water for cotton irrigation and to supply an exploding population of thirsty Egyptians, anthropogenic global warming is now increasing the rate of evaporation from Nile Reservoirs.
Water is now being taken out of the Nile faster than Mother Nature can resupply it. In addition, river-borne sediments have been trapped behind six dams, or ‘cataracts,’ including the High Aswan hydroelectric project built by the former Soviet Union.
The once lush freshwater fan shaped Nile delta, the breadbasket for Egypt, is sinking and salt water from the Mediterranean Sea is now flowing into the northern part of the delta (Do the name Ruby Begonia sound familiar to ya?). On an annual basis the Mediterranean no longer receives a net flow of river water and a productive nursery ground for fish no longer exists. At least the lack of river flow into the Mediterranean presumably precludes massive eutrophication and the development of a hypoxic zone, such as occurs each year off of the Mississippi delta.
As for comparative numbers, the drainage basin of the Mississippi River occupies 2,980,000 square kilometers, or about 1.1 million square miles, 41% of the continental US. The Nile watershed is only 4% larger, covering 3,254,555 square kilometers, or about 1.3 million square miles, 10% of the area of Africa.
According to this blogger’s friend Wikipedia, the combined delta of The Yellow and The Yangtze Rivers is the largest in the world, with an astounding area of roughly 500,000 Km2. Second, at about 350,000 Km2 is the combined delta areas of the Ganges and the Brahmaputra. In third place is the (shrinking) Mississippi River Delta, described by Wikipedia at either 96,000 or 150,000 sq km.**
I decided to use the lower number for our coast, which still seems high but somewhat more reasonable. The Amazon delta came in at about the same area as the Mississippi, at about 100,000 Km2. Finally, according to Wikipedia, the area of the Nile delta is about 25,000 Km2.
Without doubt the biggest difference between the Mississippi and Nile deltas is population density. Figure 2 shows the relative difference in watershed areas, delta areas and relative population densities between the two deltas. Notice that even when multiplied by ten the population density of south Louisiana doesn’t even show up on the pie chart for the Mississippi delta.
*Founding editor (firstname.lastname@example.org)