Oxbows and Meanders

I found this tangled map, created in 1944, over on the ever-fruitful NASA web site for the Earth Observatory. It shows historical changes along a stretch of the Mississippi River.

North of the Atchafalaya River. The 1999 satellite image shows an oxbow lake from 1785, created when a meander (a bend in the river) closes itself off to leave behind a crescent.  From the Geological Investigation of the Alluvial Valley of the Lower Mississippi River, published by the Army Corps of Engineers in 1944. Source: Earth Observatory

North of the Atchafalaya River. The 1999 satellite image shows an oxbow lake from 1785, created when a meander (a bend in the river) closes itself off to leave behind a crescent.
From the Geological Investigation of the Alluvial Valley of the Lower Mississippi River, published by the Army Corps of Engineers in 1944.
Source: NASA/Earth Observatory

I stumbled upon it while looking at a small collection of river surveys from 1865, and comparing them to modern Google maps. There was this one, a stretch just south of St. Mary, Missouri.

Sheet 6 of the 1865 U.S. Coast Survey Map of the Mississippi River from Cairo, IL to St. Marys, MO.  Source: Wikimedia

Sheet 6 of the 1865 U.S. Coast Survey Map of the Mississippi River from Cairo, IL to St. Mary, MO.
Source: Wikimedia

The modern one looks a bit different – fewer bends, fewer islands – but not so much that it would be unrecognizable. Notably, the large bend that once branched off to St. Mary, Missouri, visible at the top of each map, is now just a small tributary.

One might have expected more of a difference over the course of 150 years of population increase and civil engineering.

The same stretch of river, with St. Mary, Missouri in the upper left corner.  Source: Googlemaps

The same stretch of river, with St. Mary, Missouri in the upper left corner.
Source: Googlemaps

But, at least on the Mississippi, the differences in major river flow come when the river is left alone to shift, meander, silt up and sidle over. The more humans work on this particular river, the more it stays the same. Levees are installed to prevent overflow (although they don’t always work).

The entire Mississippi Delta once shifted every 1,000 years or so – but with industries and port installations firmly established over the course of a few human generations, that would be an economic disaster. The Old River Control Structure, undertaken in the 1950s, keeps the delta in place.

More or less. At least, for the time being.

Because in the long run and when left to their own devices, rivers are all over the map.

Section of the 1944 Mississippi River Meander Belt. For more, visit here. Source: VisualNews

Section of the 1944 Mississippi River Meander Belt. For more, visit here.
Source: VisualNews

Watery Treasure

Draining swamps and wetlands has, over the course of human civilization, been seen as a way to grasp land from the greedy waters that cover most of the Earth’s surface.

Add to this that much of the drained, reclaimed land is then conveniently located on prime river or coastal property, and the terrestrial inclination to dry out wetlands makes even more sense. There’s gold in them there swamps.

A MODIS image from NASA's OceanColor Web shows floodwaters and sediment emptying into the Gulf. Source: PennNews/NASA

A MODIS image from NASA’s OceanColor Web shows floodwaters and sediment emptying into the Gulf.
Source: PennNews/NASA

Conservationists usually look at the loss of ecosystems, plant and animal life, habitat degradation and so on. But the real price of the gold rush mentality is slowly revealing itself.

The impact of river levees on flooding has become well known over the past couple of decades. Heavily developed rivers areas around the world experiencing regular and expensive inundations when water flow in flooded rivers is blocked from flowing into tributaries, marshes or swamps.

I found a report from 2005 that shows the impact of land drainage on Florida – not in terms of habitat loss, but in terms of local and regional climate change.

Human influence has transformed southern Florida. The transformation occurred not only on land converted to cropland or cities, but even in protected and undeveloped areas like the Everglades. Changes in water flows transformed deep-water sloughs into drier sawgrass marshes, and mangrove forests have shrunk dramatically. Source: NASA

Human influence has transformed southern Florida. The transformation occurred not only on land converted to cropland or cities, but even in protected and undeveloped areas like the Everglades. Changes in water flows transformed deep-water sloughs into drier sawgrass marshes, and mangrove forests have shrunk dramatically. Source: NASA

A multi-disciplinary team examined historical land cover and climate evidence from pre-development Florida (i.e. 19th-century), and found that in comparison to a drier, drained modern Florida, local climates were cooler and wetter in summer, and warmer in winter. The lack of local water cover changed local climate patterns.

This begins to get at the argument made by Sandra Postel, Director of the Global Water Policy Project, in a recent piece in National Geographic, namely, that wetlands in their watery form are worth more than the land we take from them.

She cites a new study in the journal Global Environmental Change, which shows that “the global area of freshwater wetlands and floodplains shrank by nearly two-thirds between 1997 and 2011, from an estimated 165 million hectares (408 million acres) to 60 million hectares (148 million acres).”

We’ve never been very good at weighing intangibles against objects of  immediate human value, like land. But Postel makes the argument for putting wetland and watershed services in a language we understand: Money.

Landsat images clearly show different types of landcover in southern Florida. Source: NASA/Robert Simmon

Landsat images clearly show different types of landcover in southern Florida.
Source: NASA/Robert Simmon

Citing the role of wetlands, like those that have been drained in Florida, as well as coral reefs, marshes and tropical forests, in mitigating flood and drought, the research team put together a list of water ‘services’ provided. These include recharging groundwater and filtering water in lakes and rivers, maintaining water levels that facilitate shipping, and several other long-term uses.

The total value of global ecosystem services to humans was evaluated at $120 trillion/year (for 2011). This is compared to a global GDP of  $75.2 trillion/year for the same year.

Now, the question is this:

If we look at everything through the lens of cost effectiveness, do we really believe humans can provide all the same services at a better price, even assuming we could develop the technology to do so?

Is a new condo development, mall, golf course or business center really the most cost efficient way to make use of the golden value of the world’s wetlands?