OK, truth be told, we stretched reality just a bit when referring to flooding. In an effort to make the history of the Salton Sea more interesting, we attempted to entice readers to continue reading by having each month end with a bit of a cliff hanger. Usually an allusion to flooding and ensuing destruction or some other calamity was made. It turns out flooding wasn’t an immediate danger. It was more of a long term danger.
The issue that had most experts of the day concerned was a type of erosion known as headward erosion or cutback. To picture what it looks like, think of Niagara Falls, but on a smaller scale. As water from the Colorado River flowed north along the channel of the New River into the Salton Sink, it produced a cutback that moved in the opposite direction. Unlike the slowly moving Niagara Falls cutback, thanks to the alluvial soil, the cutback along the New River channel moved quite rapidly. During periods when the water flow rate was very high, the cutback could move almost a mile a day.
The surface of the Salton Sea today is several hundred feet below sea level. The New River, where it crosses the US / Mexican border is a couple of feet above sea level. As the cutback moved southward, it carved out a canyon similar to the Grand Canyon, but again, on a smaller scale. The rising altitude of the land caused the height of the cutback grow larger and larger, approaching a hundred feet. Evidence of the flooding and headward errosion is still visible today along the New River channel.
If the cutback were allowed to move all the way to the Yuma, AZ region it would permanently shift the flow of the Colorado River into the Salton Sink and Imperial Valley. That was the real danger. Although, again, not an immediate danger.
We wanted to know how much water the Salton Sink, Coachella and Imperial Valleys, and entire surrounding area that is below sea level could hold, so we consulted a couple of geologists. The calculations varied slightly, but all the estimates came in at around 700 cubic miles of water. It actually holds a bit more because the land in Mexico between the Gulf of California / Sea of Cortez and the a fore mentioned areas is a couple of feet above sea level. 700 doesn’t seem like that big a number, but if it was taken from the ocean it would lower sea levels around the world by almost an inch. Not so bad considering global warming.
The average annual flow of the Colorado River is measured in acre feet, but when converted to cubic miles, works out to about 5 cubic miles of water. Yup, do the math on that one and you can see that it would take a really, really, long time to completely flood entire basin. Factoring in absorption and evaporation means that it would probably take about 200 years to flood the entire region. That’s plenty of time to move farms out of harms way.