BOARD02384

• Board Meeting Date: 1/24/2006
• Description: WSP Section - Presentation by Tim Carlson of the Tamarisk Coalition
• Board Meetings - Doc Type: Memo

.

.

TamariskC.oll
eWeB Presentation, 1-25-2006

:.2.. The Colorado River has 6,465 total acres of tamarisk infestation <:It approximately 37% average density. Because
the Color:.H.lo River is more incised than the hroad floodplain of the Arkansas River, its tal11Jrisk infestations are
n~llT(jWl'l', ;lvcraging :356 feet in width.

3. The Purgatoire River has both broad floodplains and a I1Jrrow canyon section. As a result it has signitic<lnt areas of
infestJtion (9,316 acres) but has a low averfJge density of 25%.

4. The IIll)S! infested area is located around .John IvIartill Reservoir (5,567 acres) and is 7,000 feet wide at one point.

5. The lll<Jjor trihul::lries for the three rivers had an additional 6,685 acres of infestation y.,;th an average density of
Jpproximatcly 30%. FOlmlain Creek and the HueIlano River, both tributaries to the Arkansas River, accounted for
more lh;.Hl 50% of the overall infested acres for tributaries.

6. Current water losses are based on the amount of water tamarisk is cunently using under observed densities minus
the water that would be used by native plants. Figure 1 represents the differences in vegetative cover \vith and
without tamarisk and illustrates how tamarisk will occupy an area much greater than the riparian zone which
typically would support cottonwoods and willov....s, also phreatophytes. The significant water losses occur as
tamarisk occupies upland areas v...ithin the floodplain that would nonnaUy have dlyland xeric vegetation such as
grasses, SJge, rabbit brush, etc. For much of the Arkansas River, with its broad floodplain, this upland area is
typicall).' 80% of the infested area; whereas, the Colorado River generally has upland areas ranging between 50%
Lind 75%. Based on these conditions, the estimates of cunent water losses above and beyond what native vegetation
\vmJld LIse are:
a. Colorado R.iver = 7,392 acre-feet per year.
b. Arkansas River = 5:1,834 acre-feet per year.
c. Purgatoire River = 7,412 acre-feet per year.
d. Trihutaries = 6,031 acre-feet per year.

7. Future water losses ;)ssume an infilling of the existing infestation areas that \villlikely occur over the next several
Jec~j(jcs based on similar conditions observed in other states (NM, UT, and NV). Future water losses from infilling
only (no expansion from existing infested areas) are estimated to be:
a. Colorado River = 19,705 acre-feet per year.
h. Arkansas R..iver = 94,119 acre-feet per year.
c. Purgatoire River = 31,193 acre-feet per year.
d. Tributaries = :.w,644 acre-feet per year.

2