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After 20 years of negotiations between seven US states, Mexico and a range of NGOs, the salt-caked wasteland of the long-dry Colorado River Delta is set for a burst of new life in an unprecedented ecological experiment.
The once-mighty Colorado has been progressively dammed over the past 90 years, with eight dams, including America’s largest - the Hoover - having left its Mexico delta completely dry for most of the past 40 years.
A “pulse” of 130 billion litres of water is currently wending its way across the delta in an eight-week revitalisation phase.
Two Deakin researchers are in Mexico witnessing the event, and assisting in monitoring its effects. Dr Rebecca Lester, Senior Lecturer in Freshwater Ecology, and Research Academic Dr Jan Barton, both from Deakin’s School of Life and Environmental Sciences and Centre for Integrative Ecology (CIE), have joined US scientists for 10 days, following the water’s edges and taking samples as they go.
The two Deakin scientists have been working on the project with Professor Karl Flessa, from the University of Arizona, who is the US Chief Scientist for this project, overseeing the US scientific monitoring of the flow, and who has recently been in Australia, as “visiting scientist” at CSIRO. The researchers have been collaborating on environmental flows in the Murray-Darling and the Colorado River, as the two rivers are very similar from a climatic and hydrologic perspective.
The sluices on the Colorado opened on March 23, beginning an occurrence similar to a small spring flood - the system's historic natural cycle - that is expected to support verdant life, separating the river from the desert, and allowing the re-emergence of trees such as native willow and native cottonwood, the latter of which has evolved to grow at a phenomenal pace during flood conditions.
Cottonwood roots can grow up to 2.5 centimetres a day as they pursue retreating groundwater. Currently, only three per cent of the original quantity of cottonwood and willow trees remains.
“This pulse will assist the river ecosystem to regenerate, and perhaps enable it to persist until the next flows come through the region,” Dr Lester said.
While she is not optimistic that the delta will continue to have flow beyond the pulse phase, she “is more optimistic that future events such as this can be achieved, and that perhaps, through time, more regular flow will be possible, despite competing demands.”
The Deakin researchers have joined approximately 40 scientists from institutions, such as the University of Arizona, the Universidad Autonoma de Baja California (Mexico), the United States Geological Survey and The Nature Conservancy.
The scientists are closely monitoring the event, installing temperature and moisture sensors, some of which have been buried up to 10 metres below the surface, to measure how deeply and how quickly the water seeps below the surface. Satellite imagery of vegetation growth and laser scans of the flood plain will also help to measure the return of life to the delta.
An El Niño flood returned water temporarily to the area in parts of the ‘90s, giving a hint of what the restored delta could be like, with saplings appearing as soon as three weeks after water reintroduction.
In the lead up to the pulse, the water was slowly released from three of the northern dams in the United States, so that it could be released to the Delta from the southernmost dam, Morelos, on the Mexican-US border. Until now, this dam has diverted what was left of the river into the irrigated fields of the Mexicali Valley.
The agreement, called Minute 319, is significant in that it is the first time that water has crossed the US-Mexico border for environmental purposes. Apart from allowing for this pulse flow, it includes the provision of $21 million by the US to assist with water-saving measures in Mexico and an agreement to share in shortages, allowing Mexico to store water in US dams (as it doesn’t have any itself).
A separate Water Treaty provides a legal framework to define the water rights of all parties, which has been designed to forestall conflict about how much water the US is obliged to flow into Mexico, a potential “sticking point,” given climate modelling predicts increasing aridity for the region.
After the initial pulse, a small flow will continue, providing an extra 64 billion litres over the next three years. While this is still much lower than the delta’s original “natural” saturation, researchers hope that around 950 hectares of the area will return to life, increasing the habitat for 380 species of native plants and animals, including 30 species of “stopover” migratory birds.
More details about the Colorado Delta flow can be found at the following sites: