An engineered flood has brought vegetation back to the lower Colorado River delta. The water pulse from the Morelos Dam took place last March after an agreement between the US and Mexican governments and results just released by the US Geological Survey and US Bureau of Reclamation show that it has had an overwhelmingly positive effect.
Between 23 March and 18 May around 130 million cubic metres of water was released into the dry riverbed below the Morelos Dam. The dam straddles the US-Mexican border west of Yuma.
‘The groundwater was recharged, vegetation got greener than previous years and the water helped germinate new native vegetation,’ says Karl Flessa, a University of Arizona professor of geosciences. ‘As a bonus, the river reached the sea.’
People living along the river course also benefited. For many it was the first time they’d seen the river.
The water eventually soaked into the ground 37 miles below the dam, but the surface flow expanded further than had been hoped. The new studies show that the increase in groundwater revived vegetation along the 83-mile route to the sea. This allowed willows and cottonwoods to germinate.
‘So long as the roots get down into the permanent water table, then you have established a new bunch of trees that will live for 20, 30, even 40 years,’ Flessa says. ‘Those trees will attract birds.’
Scientists have already noticed an increase in the number of birds along the watercourse. Farmers will also benefit from an increase in the water table, which can be pumped to irrigate fields.
The pulse flow came about under the Minute 319 agreement between the US and Mexico. This agreement helps to regulate water surpluses and flows on the Colorado River for benefit of both countries. ‘Another pulse flow would require a new agreement, because Minute 319 calls for only one pulse flow within the five-year term of the minute,’ Flessa says. ‘We hope the results of this pulse flow encourage the negotiators to make this happen again.’