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

3) Estimates on water consumption by tamarisk vary a great deal depending on location,
maturity, density of infestation, and depth to groundwater. Using past research,
tamarisk will generally use approximately 1 foot per year more than a cottonwood and
willow community and 4 feet per year more than an upland plant community of native
grasses/sage/rabbit brush Russian-olive has similar non-beneficial use values. For
Colorado, based on 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. Using the
estimated infested acreage of 57,000 acres in Colorado, the predicted non-beneficial
water consumption is approximately 170,000 acre- feet per year.

4) The impact of uncontrolled tamarisk infestation over the next 50 years is a water loss
ranging from 290,000 to 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.

5) Costs for removal vary depending on the expanse of the infestation, existence of other
valuable plant species, and terrain. Aerial helicopter spraying with herbicide has a cost
between $200 and $250 per acre, Irechanical mulching and herbicide application ranges
in cost from $300 to $800 per acre, and hmd clearing and herbicide application ranges
from $1,500 to $5,000 per acre. Additionally, a new bio-control approach that uses a
Chinese leaf beetle is being researched by the U.S. Departments of Interior and
Agriculture and may help further to reduce costs. No one approach is right for all
situations; Integrated Pest Management that matches the right methods for each
situation is the recommended strategy by the Colorado Department of Agriculture.

6) Removal is only part of the cost. Restoration is the other component which is necessary
to bring back the right native plants and restore habitat. Restoration may occur
naturally where native plants are still viable or may require specialized efforts. In
general, costs range from $50 to $1,500 per acre.

7) Using an average cost of tamarisk control and revegetation of $750/acre, 57,000 acres
of infestation in 2003, and 170,000 acre- feet of water potentially saved within Colorado;
the resulting overall cost for control and revegetation is $43,000,000 or approximately
$250 per acre- foot of water resources recovered.

8) Beyond improving the abundance of water, the extremely important side benefits of
tamarisk control and riparian restoration are:
>> Enhanced water quality,
>> Improved wildlife habitat,
>> Greater bio-diversity among both plants and animals, and
>> Improved conditions for human enjoyment of the river systems.

There are still several areas of research needed to complete the understanding of the tamarisk
problem in Colorado. These areas are highlighted in the report and can be supported by current
legislative efforts within the U.S. Congress (H.R. 695 and H.R. and S. 1051, S. 1236).

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