So Goes the Colorado

 

Click to enlarge -- notice the tan hash-marked areas.

I follow the Facebook page Geomorphology Rules because it so often features maps like this one -- maps that tell a provocative story. I also follow it because my master's research was in fluvial geomorphology and I enjoy staying in contact (pun intended) with that quirky discipline that lies at the juncture of geography and geology. Plus which, geographer Kathleen Nicoll runs the site with equal measures of wit and wisdom.

The first thing I noticed about this map is that it identifies the Grand Canyon as a convenient divide between the upper and lower portions of the Colorado River drainage basin. I later noticed that this map (or perhaps it is a map excerpt) has no title or discernible producer.

But the most important thing about this map is that it explains why the Colorado River does not reach the sea most of the time. Most maps show it connecting to the Gulf of California, but in real life this is rare. Where Arizona, California, and Baja California meet, the river is scarcely 100 feet wide; immediately south of that it is not much wider than the small living room in which write this. 

And a few miles south of that, the bridge ("puente") that carries Mexico's Route 2 over the river is bridge over sand most of the time.

I have often explained this in terms of the unfair division of the river's water resources between the upstream and downstream neighbors. Octavio Paz famously lamented, "Alas, poor Mexico! So far from God and so close to the United States!" A century ago, the neighbors agreed to go "halfsies" on the basin's water, with each being allocated 7 million acre-feet of the total 14 million discharged annually. The agreement was made during an unusually wet period, but the U.S. always takes its half, since Mexico cannot come upstream to get it. Agribusiness and urban areas in the basin -- including the one I was living in when I learned all of this -- reduce the river to a trickle.

The maps makes clear, however, that this is not a full explanation of the problem. Rather, it is the interbasin transfers to the relatively small areas that essentially surround the basin. These are small regions to which water that would otherwise be making its way toward the aforementioned bridge is instead crossing the divide to supply cities, farms, or both in other basins.

The most notorious of these arrangements is the focus of the 1974 film Chinatown, but Los Angeles is far from the only culprit at this stage.