‘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?
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.
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.