BOARD01713

• Board Meeting Date: 7/28/2003
• Description: CF Section - Tamarisk Control and Eradication Update
• Board Meetings - Doc Type: Memo

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Impact of Tamarisk Infestation on the
Water Resources of Colorado
May 30, 2003

cottonwood/willow community. Using the above information, one can reasonably estimate that
this non-beneficial use of water is approximately I foot per year for tamarisk and Russian-olive
for the riparian areas that could support a cottonwood/willow community and 4 feet per year for
the upland areas that could support a native grasses/sage/rabbit brush community. For Colorado,
based on personal observation, it is estimated that one-third of the land currently infested by
tamarisk and Russian-olive was formerly occupied by cottonwood/willow communities and two-
thirds by grasses/sage/rabbit brush communities. If one takes the estimated infested acreage of
57,000 acres in Colorado, the estimated norrbeneficial water consumption is approximately
170,000 acre-feet per year. [Note: based on current information that was presented at the annual
Saltcedar Bio-control Consortium meeting (February 19-21, 2003) in Albuquerque, the ratio of
native plant habitats that tamarisk now occupies is believed by many researchers to closer
approximate 20% for cottonwood/willow communities and 80% for grasses/sage/rabbit brush
communities for much of the West This would lead to a somewhat higher non-beneficial water
consumption estimate.]

The impact of uncontrolled tamarisk infestation is presented in Figure 12 over the next 50 years
based on a modest growth rate of 1 percent per year and a moderate growth rate of 2.5 percent
per year. Under these conditions the amount of water lost in a non-beneficial manner will range
between 290,000 and nearly 600,000 acre-feet of water per year. By comparison, the Denver
Water Board serviced 1,100,000 people with 250,000 acre-feet of water in 2001 (Denver 2002).

Research Need - The actual norrbeneficial use of water by tamarisk in Colorado's
different ecological ~ttings needs to be established. Existing research should be
used and augmented with on-the-ground measurements of changes to both stream
flow and groundwater before and after tamarisk control activities. This research will
help to establish the differen;e in water consumption between non-native
phreatophytes and typical riparian, floodplain, and adjacent upland plant
communities on an acre-foot/year per acre basis as a function of thicket maturity,
floodplain morphology, climatic conditions, geology, and geographic location.
These differences will help establish the non-beneficial use of water by these non-
native plants in comparison to a healthy riparian ecosystem. The understanding of
this non-beneficial use value is essential to the gaining of a consensus on the impact
that tamarisk has imposed, and what benefits can be expected if control and
revegetation take place on a broad scale.

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