Tuesday, April 19, 2011

Phreatophytes - Control 'em Or Not!

Another one of those "I wish I knew" issues.  Phreatophyte control is an "on again, off again" water management issue that keeps popping up in the West.  It started in the 1940's, peaked again in the late 1960's and is resurging again in the mid-2000's.  It's always a question of water supply, riparian habitat and aquatic species impacts - usually in that order.

No one doubts that  these trees, which are deep rooted, can and do use groundwater.  In Kansas these tree species mainly include Tamarisk, Cottonwood, Russian Olive and Willow.  How much water they use is not all that much at issue either - it's considered from hearty to prodigious.  What is not clearly understood is their real impacts on the base flows of adjacent creeks, streams and rivers.

Many reports say their impact on baseflows is significant.  Many others say not so.  Most reports I have reviewed start with the assumption that they do affect baseflows, then work all kinds of magic with ET numbers to quantify that impact and conclude that eradication will subsequently free up X thousand acrefeet of water per year for other uses.  A few reports consider the replacement growth's ET requirements and moderate the saved water numbers in various degrees - all the way to no net increase in baseflow at all.  I found one report that says the impact on adjacent drainage baseflows depends on the nature of the creek and it's contribution drainage area - in cases where baseflow is a small component of streamflow, large-scale phreatophyte clearing in combination with sound range management will not lead to any increases in streamflow.  This of course, implies that where these conditions are not the case...

I will admit the majority of reports are in the camp of "..clear the water-robbing suckers out of the way, man..", but I'm not so sure.  It is an expensive procedure that requires a lot of maintenace and follow-up for a long time.  I guess I'm looking for the definitive compendium on phreatophytes, water supply, species impacts and habitat changes associated with this practice - taking into account the various climate regions, soil regimes, runoff ranges and whatever else is likely to affect these relationships.

BTW, this is another of the water conservation efforts Nebraska is proposing to do in the Republican River Compact area to placate Kansas. 'nuf said.

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