Event Title

Chicken or Egg? Floodplain Sedimentation as the Precursor or Result of Tamarisk Invasion?

Location

Eccles Conference Center

Event Website

http://water.usu.edu/

Start Date

3-27-2006 5:45 PM

End Date

3-27-2006 6:00 PM

Description

Channel narrowing on the Upper Green River of Colorado and Utah is well documented. Regulation, invasive riparian vegetation, and climatic shifts have all been implicated as agents of riparian and aquatic habitat changes. However, the rates and timing of floodplain sedimentation events leading to the degradation of aquatic habitat and riparian forest alteration are poorly constrained. Previous work has used aerial photos, GIS analysis and replicate ground photos to document 20th century floodplain building. To describe modern fluvial-riparian interactions, we documented bed, bank and, floodplain response to large floods from Flaming Gorge Dam in tamarisk control and removal reaches of Lodore Canyon of the Green River in Dinosaur National Monument, a brisfan controlled canyon, similar to the Grand Canyon. To obtain the rates and timing of 20th century floodplain sedimentation events we excavated large trenches through known accreted surfaces in Lodore Canyon and Brown’s Park. We used changes in the stem anatomy of tamarisk samples, local rating curves and, stratigraphic analysis to precisely age date the deposited sediments. Initial results show that significant floodplain accretion occurred when FGD began operations in the fall of 1962 and abandoned the floodplain deposits from the summer 1962 flood. Additional floodplain accretion occurred in 1983, the first flood significantly greater than FGD powerplant capacity. Modern channel response to floods indicates that past floodplain sedimentation events could have occurred independent of riparian vegetation invasion. The Green River in Brown’s Park shows potential for continued narrowing, while Lodore Canyon appears to be near an equilibrium state with the current hydrologic regime.

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Mar 27th, 5:45 PM Mar 27th, 6:00 PM

Chicken or Egg? Floodplain Sedimentation as the Precursor or Result of Tamarisk Invasion?

Eccles Conference Center

Channel narrowing on the Upper Green River of Colorado and Utah is well documented. Regulation, invasive riparian vegetation, and climatic shifts have all been implicated as agents of riparian and aquatic habitat changes. However, the rates and timing of floodplain sedimentation events leading to the degradation of aquatic habitat and riparian forest alteration are poorly constrained. Previous work has used aerial photos, GIS analysis and replicate ground photos to document 20th century floodplain building. To describe modern fluvial-riparian interactions, we documented bed, bank and, floodplain response to large floods from Flaming Gorge Dam in tamarisk control and removal reaches of Lodore Canyon of the Green River in Dinosaur National Monument, a brisfan controlled canyon, similar to the Grand Canyon. To obtain the rates and timing of 20th century floodplain sedimentation events we excavated large trenches through known accreted surfaces in Lodore Canyon and Brown’s Park. We used changes in the stem anatomy of tamarisk samples, local rating curves and, stratigraphic analysis to precisely age date the deposited sediments. Initial results show that significant floodplain accretion occurred when FGD began operations in the fall of 1962 and abandoned the floodplain deposits from the summer 1962 flood. Additional floodplain accretion occurred in 1983, the first flood significantly greater than FGD powerplant capacity. Modern channel response to floods indicates that past floodplain sedimentation events could have occurred independent of riparian vegetation invasion. The Green River in Brown’s Park shows potential for continued narrowing, while Lodore Canyon appears to be near an equilibrium state with the current hydrologic regime.

https://digitalcommons.usu.edu/runoff/2006/AllAbstracts/39