The Southwest, for thousands of years, has undergone episodes of arroyo cutting, times when vertical-walled drainage ways cut deeply into soft valley fill. Whether arroyo cutting was a result of falling water tables or falling water tables resulted in arroyo cutting is an interesting question. Certainly an arroyo cut into wet ground will allow seepage into the waterway, ultimately dropping the water table unless sufficient precipitation falls to replenish the lost water. On the other hand, it's difficult for a waterway to excavate its bed into saturated soil.
Be that as it may, arroyo cutting has dramatic effects on plant life.
Roots that once reached ground water are suddenly dependent on precipitation alone, and
only shrubs capable of reaching deep into the ground in search of water are able to
survive. Even today, areas cut by deep arroyos are almost barren, but historically
supported grasses thick enough to be harvested for hay. The difference between mesquite
scrub and grasses as high as the stirrup of a horse gives a whole new meaning to the
term, "high water".
Listen to the Audio (mp3 format) as
recorded by KTEP, Public Radio for the Southwest.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.