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Open-File Report 2014–1095

Prepared in cooperation with AMS Consultants

State-and-Transition Prototype Model of Riparian Vegetation Downstream of Glen Canyon Dam, Arizona

By Barbara E. Ralston, Anthony M. Starfield, Ronald S. Black, and Robert A. Van Lonkhuyzen


Facing an altered riparian plant community dominated by nonnative species, resource managers are increasingly interested in understanding how to manage and promote healthy riparian habitats in which native species dominate. For regulated rivers, managing flows is one tool resource managers consider to achieve these goals. Among many factors that can influence riparian community composition, hydrology is a primary forcing variable. Frame-based models, used successfully in grassland systems, provide an opportunity for stakeholders concerned with riparian systems to evaluate potential riparian vegetation responses to alternative flows. Frame-based, state-and-transition models of riparian vegetation for reattachment bars, separation bars, and the channel margin found on the Colorado River downstream of Glen Canyon Dam were constructed using information from the literature. Frame-based models can be simple spreadsheet models (created in Microsoft® Excel) or developed further with programming languages (for example, C-sharp). The models described here include seven community states and five dam operations that cause transitions between states. Each model divides operations into growing (April–September) and non-growing seasons (October–March) and incorporates upper and lower bar models, using stage elevation as a division. The inputs (operations) can be used by stakeholders to evaluate flows that may promote dynamic riparian vegetation states, or identify those flow options that may promote less desirable states (for example, Tamarisk [Tamarix sp.] temporarily flooded shrubland). This prototype model, although simple, can still elicit discussion about operational options and vegetation response.

First posted May 9, 2014

For additional information, contact:
SBSC staff, Southwest Biological Science Center
U.S. Geological Survey
2255 N. Gemini Drive
Flagstaff, AZ 86001

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Suggested citation:

Ralston, B.E., Starfield, A.M., Black, R.S., and Van Lonkhuyzen, R.A., 2014, State-and-transition prototype model of riparian vegetation downstream of Glen Canyon Dam, Arizona: U.S. Geological Survey Open-File Report 2014-1095, 26 p.,

ISSN 2331-1258 (online)





Model Parameters—Glen Canyon Dam Releases, Floodplain Categories, and Riparian Vegetation Associations



References Cited

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