#delta

Oxbows and Meanders

/ PK Read / Leave a comment

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

Pulse Taking

/ PK Read / Leave a comment

‘Long memory’ is a term used in probability analysis. It originated in hydrology to predict flood patterns on the Nile River.

But do rivers remember where they once flowed?

Floraskin – Huth & Domenig Via: Data Is Nature

Floraskin – Huth & Domenig
Via: Data Is Nature

A large pulse of water was released along the Colorado River this year, an historic ecological undertaking meant to restore the once-lush downriver sections and delta. The goal of the 130 billion-liter (34 bn gallon) pulse was to imitate the spring floodwaters that once coursed the length of the river, but which have been diverted for other uses further upstream.

These images show the river before and after the water pulse was released. The river bed and tributary channels have been little more than dry markers for the memory of a river that once carried 18.5 trillion liters (4.9 trillion gallons) of water every year.

Before: An April 2013 view shows the dry river shell in northern Mexico. Credit: NASA Earth Observatory image by Robert Simmon, using Landsat 8 data from the U.S. Geological Survey

Before: An April 2013 view shows the dry river shell in northern Mexico.
Credit: NASA Earth Observatory image by Robert Simmon, using Landsat 8 data from the U.S. Geological Survey

After: Water flows through the same area, April 2014. Credit: NASA Earth Observatory image by Robert Simmon, using Landsat 8 data from the U.S. Geological Survey

After: Water flows through the same area, April 2014.
Credit: NASA Earth Observatory image by Robert Simmon, using Landsat 8 data from the U.S. Geological Survey

The final destination of the water is the Colorado Delta, which once formed a rich connection between the river and the Gulf of Mexico. The Delta has rarely seen river water since 1960.

As it turns out, the water pulse may not reach the Delta at all. Sand bars and shrubs are slowing the flow, even as conservationists work to re-establish trees and wetlands in its wake.

If there is such a thing, the long memory of the Colorado River may have to wait a while longer before it once again meets the Gulf of Mexico at the end of a long journey home.

 

http://www.livescience.com/45281-colorado-river-pulse-satellite.html

Transboundary Pulse

/ PK Read / Leave a comment

It’s a strange notion, the cutting off of water across an invisible territorial boundary. There are few actions we can take as humans – both for communities and for the environment – that are more baldly assertive than diverting rivers and water flow.

The Colorado River delta sits at the very end of the 2330 km-long (1450 m.) Colorado River, which winds southward from Colorado to the Sea of Cortez in Mexico. An object of human geo-engineering for hundreds of years, it’s only in the last century that the Colorado River became one of the most controlled, divided and litigated rivers in the world.

Over the past fifty years, so much water has been used in the United States that the river hasn’t reached the delta or the Sea of Cortez at all, turning what was once a lush system of lakes and marshes into a parched desert.

Collage of historical descriptions of the delta and an image of the dry delta of recent years. "The river enters the sea by a mouth four leagues wide...The Rio Colorado bathes (the land) like the Nile bathes Egypt, giving it great fertility." Source: Jordan Wirfs-Brock/

Collage of historical descriptions of the delta and an image of the dry delta of recent years. “The river enters the sea by a mouth four leagues wide…The Rio Colorado bathes (the land) like the Nile bathes Egypt, giving it great fertility.”
Source: Jordan Wirfs-Brock/Univ. of Colorado Boulder

But this week, for the first time in five decades and timed to coincide with World Water Day, water from the Colorado River flowed at more than a trickle on the southern side of the border in Mexico.

In 2012, the 1944 U.S.-Mexico treaty on river use was amended with an addition known as Minute 319, which aims to support reclamation of the delta through controlled ‘pulse flows’, large surges of water that then trickle off in an imitation of the pre-dam, pre-diversion river that flowed heavily with the snow melt in spring and tapered off through later months.

The surges created by this pilot project should help spread tree and plant seeds across the delta, while the tapering off should provide irrigation for plants to thrive. It’s hoped the influx of water and the re-establishment of plant life will also support the delta’s dwindling wildlife, including many species of migratory birds.

It’s an unusual cross-border project in that the water release isn’t specifically for commercial purposes, but to support environmental restoration.

Cross-border water cooperation and sharing to support ecosystem recovery: I suppose these days, that’s a strange notion, as well.

Colorado River Dry Delta, terminus of the Colorado River in the Sonoran Desert of Baja California and Sonora, Mexico, ending about 5 miles north of the Sea of Cortez (Gulf of California). Photo: Peter McBride USGS / Wikipedia

Colorado River Dry Delta, terminus of the Colorado River in the Sonoran Desert of Baja California and Sonora, Mexico, ending about 5 miles north of the Sea of Cortez (Gulf of California).
Photo: Peter McBride USGS / Wikipedia

Think of it as a surge of water. It’s what happens when there’s a big rainfall or the snow melts into a river. The flow increases for a few days or weeks, and then it goes back to normal. Rather than weather, this environmental experiment will be a release of water from a reservoir. It is designed to mimic the kind of natural pulse flows that help keep rivers healthy by spreading native plant seeds and creating conditions for those seedlings to grow and thrive. – See more at: http://www.nature.org/ourinitiatives/regions/northamerica/areas/coloradoriver/colorado-river-pulse-flow-qa-with-eloise-kendy.xml#sthash.2WwHpQtj.dpuf
Think of it as a surge of water. It’s what happens when there’s a big rainfall or the snow melts into a river. The flow increases for a few days or weeks, and then it goes back to normal. Rather than weather, this environmental experiment will be a release of water from a reservoir. It is designed to mimic the kind of natural pulse flows that help keep rivers healthy by spreading native plant seeds and creating conditions for those seedlings to grow and thrive. – See more at: http://www.nature.org/ourinitiatives/regions/northamerica/areas/coloradoriver/colorado-river-pulse-flow-qa-with-eloise-kendy.xml#sthash.2WwHpQtj.dpuf
Think of it as a surge of water. It’s what happens when there’s a big rainfall or the snow melts into a river. The flow increases for a few days or weeks, and then it goes back to normal. Rather than weather, this environmental experiment will be a release of water from a reservoir. It is designed to mimic the kind of natural pulse flows that help keep rivers healthy by spreading native plant seeds and creating conditions for those seedlings to grow and thrive. – See more at: http://www.nature.org/ourinitiatives/regions/northamerica/areas/coloradoriver/colorado-river-pulse-flow-qa-with-eloise-kendy.xml#sthash.2WwHpQtj.dpuf