The Tamarisk Coalition received a $50,000 grant from the Colorado Water Conservation Board (CWCB) to perform an inventory of tamarisk infestations on the Colorado and Arkansas Rivers within the state. The purpose of this work was to establish and implement an inventory protocol that is economical to perform and would provide a clear understanding of the extent of the tamarisk problem. The Colorado River and Arkansas River watersheds are identified because they are heavily infested and represent two distinct topographic conditions – a western slope canyon setting that is predominantly Federal lands and a front range prairie setting that is predominantly private agricultural lands. A survey of the Purgatoire River in southeastern Colorado was completed with local funding and this information is included within this summary report. The Yampa River and its tributaries, and the headwaters of the Dolores to McPhee Reservoir were also surveyed; however, this information is currently being analyzed and is not yet available.

Inventory and mapping were performed during the summer and fall of 2005 and coordinated with the U.S. Geological Survey’s (USGS) efforts at establishing a national on-line database which would conform to the weed mapping standards developed by the North American Weed Management Association. The basic approach was to use existing aerial photography and satellite imagery and local knowledge available from counties, river districts, soil and water conservation districts, state agencies, Army Corps of Engineers, National Resources Conservation Service, USGS, CSU, and The Nature Conservancy. This information was then “ground-truthed” by a 2-man team to confirm infestation density, maturity, terrain, presence of native species, and several other site characteristics. GPS data and digital photo records were taken and shape files were developed utilizing GIS capabilities at Mesa State College. Over 800 miles on the Colorado, Arkansas, and Purgatoire rivers and their major tributaries were surveyed using this approach. This information, in the form of shape files and characteristics data, has been transformed into a digital GIS database which soon will be available on the USGS invasive species website, www.niiss.org.

The full project results may be found here.The inventory summary for the three river systems is presented in Tables 1 and 2. Tributary information is presented in Tables 3 and 4. Tables 1 and 3 present the general mapping data; whereas, Tables 2 and 4 provide information on estimated current water and future water losses associated with the tamarisk infestations and the estimated costs for tamarisk control and revegetation. Table 5 and 6 summarize the costs and water impacts respectively. These water losses and cost estimates are based on the most recent research and statistical analysis available through the USDA, NOAA, USGS, CSU, National Invasive Species Council, Tamarisk Coalition, and others.