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Thursday, October 29, 2015


Steve Cole writes:

On the high plains of the Texas Panhandle, we have these things called "playa lakes" which are a unique feature of the region. "Playa" is the Spanish word for "dried-up lakebed" and so a "playa lake" is what happens when rain fills up a playa basin. (The soil here has a lot of clay so the lower parts of the playas have clay beds about as permeable as the average dinner plate. Nothing soaks in.)

While this area has the occasional stream (with actual rivers 50 miles north and 20 miles south of Amarillo), mostly it's just flat. Not as flat as a pool table, but the change in elevation rarely exceeds 10 feet in a mile. The land is divided up into unconnected drainage areas each of which are one to five miles across with a playa basin in the middle. Playa lakes can be as small as a bathtub or as big as 200 acres. [In all fairness, those rivers I mention are fairly tiny streams 10-20 feet across and 1-2 feet deep, but they sit at the bottom of massive canyons a mile wide and 500 feet deep. This is because in this dry region we get no rain for weeks then a LOT of rain all at once.]

The key thing about playa lakes is that they have no inlet (except rain) and no outlet (except evaporation). It doesn't rain that often here. We get 22 inches a year, but usually get a third of that in one week at some random point, and this year we got all 22 inches in the first six months with more to come. (This is good since otherwise farmers have to pump water from deep wells.) Given rain, the dry basins suddenly become charming little playa lakes that last a week or two. Maybe 2-10 square miles of rainfall will drain into a playa lake that is the size of a few football fields, resulting in several feet of water. This gets really bad in urban areas where most of the soil is covered by streets, buildings, and sidewalks so everything flows off into the playas.

When it rains a LOT the charming playa lakes just keep growing because they don't have natural banks. (Given 40 days and 40 nights of rain, you'd have playa lakes miles across.) When the city expands into a playa basin (and there isn't anything else to expand into), the first houses are built on the higher ground around the edge but over time houses are built closer and closer to the dried-up lake. When we get a 100-year rain (about once a decade) the lower houses will flood.

The playas in the established parts of town are often dredged much deeper (so they will hold more runoff water; one of them is nearly 70 feet deep) and are connected to East or West Amarillo Creek by underground pipelines with extensive pump systems. The creeks drain north 50 miles into the Canadian River and then east via the Arkansas River to the Mississippi River, and thereafter to the ocean.

Below is one example, originally called Dunivan Lake and later renamed Lake Lawrence. Amarilloans call it "the ocean." It is in a major shopping area, has been dredged more than 70 feet deep, and at this point is "over-full" and flowing up into parking lots, nearby streets, and businesses. The trees seen sticking up out of the lake are over 30 feet tall.   

Below is another example called Lake McDonald. This playa is in John Stiff Park (the major park in the rich part of town) so it is maintained at a constant level (about 10 feet lower than shown here) for fishing, walking abroad, and recreating yourself. The trees in the lake are next to the submerged walking path, and you can see the top parts of a few benches extending above the water surface.