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Title: Implications for the Removal of Invasive Species in Canyon de Chelly National Monument

Author
item Simon, Andrew
item Bankhead, Natasha
item JAEGER, KRISTIN
item WOHL, ELLEN

Submitted to: Environmental and Water Resources Institute World Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2007
Publication Date: 5/7/2007
Citation: Simon, A., Bankhead, N.L., Jaeger, K., Wohl, E. 0200. Implications for the Removal of Invasive Species in Canyon de Chelly National Monument. Environmental and Water Resources Institute World Congress Proceedings. Tampa, FL. 10 p. (CD-ROM)

Interpretive Summary: In the American Southwest, floodplain vegetation was historically dominated by Fremont cottonwood. During the 20th century, however, invasive exotic species such as Tamarisk and Russian-olive began to proliferate and now comprise the large proportion of many riparian zones in the southwest USA. In Canyon de Chelly National Monument, increased channel narrowing and incision has been occurring at a faster rate compared to other drainages within the southern Colorado Plateau. The National Park Service is engaged in an experimental program to remove the invasive species Tamarisk and Russian-olive from the margins of Canyon de Chelly, Arizona. The Park Service hopes that this program will aid in returning the channels to their wide and shallow geometry characteristic of the region a century ago. Because the bank materials are dominated by sands, the added strength provided by roots is significant to bank stability. Results of iterative bank-stability modeling runs show that the effects of root reinforcement provided by Tamarisk and Russian-olive have a significant impact on bank-stability and bank-failure frequency. Removal of riparian stands of Tamarisk and Russian-olive will lead to bank instabilities and accelerated widening in Canyon de Chelly National Monument. The rate that this occurs will be a function of the frequency of moderate flows that have the ability to cause losses of matric suction from lateral infiltration. For this reason, longer-duration flows such as snowmelt hydrographs should be more critical than monsoon-type convective events.

Technical Abstract: As part of a study to investigate the causes of channel narrowing and incision in Canyon de Chelly National Monument, the effects of Tamarisk and Russian-olive on streambank stability were evaluated. Root tensile strengths and distributions in streambanks were measured and used in combination in a root-reinforcement model to estimate the additional cohesion provided to layers of each streambank. Relations between tensile strength and diameter for Tamarisk and Russian-olive were similar to other woody, riparian species. However, where the roots of other riparian species have roots concentrated in the top 1m of the soil profile, roots of Tamarisk and Russian-olive extend throughout the bank profile (to 4.3 m). That is, a cohesionless bank acquires the properties of a weakly cohesive bank due to the presence of roots, providing an average 2.8 kPa of cohesion. The effects of a series of 1.0 and 1.5 m-deep flows on bank-toe erosion, pore-pressure distributions and bank stability were evaluated. Results of iterative modeling runs show that the effects of root reinforcement provided by Tamarisk and Russian-olive have a significant impact on bank-stability and bank-failure frequency. Removal of riparian stands of Tamarisk and Russian-olive will lead to bank instabilities and accelerated widening in Canyon de Chelly National Monument. The rate that this occurs will be a function of the frequency of moderate flows that have the ability to cause losses of matric suction from lateral infiltration. For this reason, longer-duration flows such as snowmelt hydrographs should be more critical than monsoon-type convective events.