The Incredible Drinking Tree

"For every complex problem there is a simple solution; and it is always wrong."

H. L. Mencken

In his letter to the editor of the Borrego Sun and fliers appearing around Borrego, R. D. McKee claims that "tamarisk are consuming more water than all other consumers combined." He calculates that there are 9,900 tamarisk in the valley and asserts that each tree consumes 4 acre-feet of water per year, or a total of 39,600 acre-feet annually. He is wrong.

First of all, it is intuitively unlikely that a single tamarisk could consume 4 acre-feet of water per year when we know that an entire acre of irrigated, mature citrus with one tree every 20 feet actually consumes only about 3.5 acre-feet/year.

Second, it can be confirmed by observation that most or all of the water consumed by tamarisk that could have any effect on the aquifer is already included in the figures published by the BWD and, conversely, that very little, if any let alone all of it is over and above that amount as McKee asserts.

  • Tamarisk thrives primarily in or near irrigated land in Borrego
  • Once irrigation is stopped, tamarisk begins to die off
  • Farmers remove tamarisk to reduce competition for irrigation water which is already included in the BWD figures.
  • Third, McKees figures are likely skewed by the nature of the data available/not available about water use by tamarisk.

  • The BWDs consulting engineer has conducted an independent review of the literature on water use by tamarisk
  • All of the data appear to be from trees in riparian environments where water is plentiful and tamarisk water consumption is unrestricted;
  • Even so, none of it shows water use any where near as high as that postulated by McKee;
  • So far, at least, BWDs consulting engineer has uncovered no data on tamarisk water use in arid environments like the Borrego Valley;
  • There is at least some likelihood that the data available is for different species of tamarisk that may require more water than those grown in wind rows in the Borrego Valley.
  • Finally, using "tamarisk water consumption" as a search string in Google, as McKee suggests, returns a number of documents that suggest a tamarisk tree "may use up to (emphasis added) 300 gallons of water a day." None of those sampled indicated higher use than 300 gals./day. Even assuming that McKees estimate of 9,900 tamarisk in the valley is correct and allowing the contrary to fact assumption that each tree uses the maximum 300 gals./day every day, the total amount of annual water use by tamarisk is far lower than his projections indicate. Even at an overgenerous 300 gals./day, each tree would consume roughly one-third acre foot of water a year; so 9,900 tamarisk would consume at most only 3,300 acre feet per year, or less than one twelfth of what McKee claims. And, again, this is based on an obvious overstatement of tamarisk water use in Borrego Valley.

    In sum, tamarisk obviously uses water maybe enough to justify large scale removal. The cost of such removal, however, is high; so the cost/benefit ratio must be carefully calculated. The data available do not support such calculations. The BWD is looking at ways of getting more and better information.

    The question of tamarisk removal deserves careful and informed consideration. It is not, however, a silver bullet that will eliminate the overdraft in one fell swoop; so it is a disservice to the community and serious efforts to deal with our increasingly dire groundwater situation to raise false hopes by portraying it as such.

    3/25/06


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