Geospatial Analysis of Change in River
Channel Position and Riparian Vegetation

The history of 20th century changes in the landscape, river flow, climate, and development of the lower Colorado River offers clues to better understand the environmental processes and conditions needed to maintain populations of native species and ecosystems. Agriculture and development, together with dams and channelization of the river, have brought large, mostly undocumented changes to the ecosystems extending from Lake Mead to the Colorado River delta.  Habitats in the LCR change in response to invasive species, urban growth, and public works including water regulation, flood control, flow regulation, and water diversion.  These change vectors intermingle with wildlife refuges, parks, agriculture, tribal lands, water-recreation centers, mining districts, and wilderness areas. This patchwork of different ownership and management priorities, combined with severe constraints on the magnitude and timing of flow releases, leaves limited possibilities for management actions that could create positive ecosystem changes.   A thorough understanding of how the water, sediment, and ecosystems have responded to past changes would allow better forecasting of how the ecosystems and habitats may respond to alternative future changes.

Historical aerial photography beginning in the 1930s and 1940s identify historic and sometimes pre-dam conditions in both landscape and vegetation.  These images offer a base source of information and an analysis tool for research into such topics as studies of changes in riparian vegetation and habitat, surface hydrology, pre-dam conditions, land use change, and sediment sources and sinks.  Image processing and geographic information system (GIS) analysis of these photographs is necessary to make the datasets usable.  The development of a GIS database of maps and photographs is helping to provide a ready research tool for the broader LCR project. 

Aerial photography of the LCR acquired in 1938 was located in the Bureau of Reclamation Office in Boulder City, Nevada.  This dataset was acquired through a “Memorandum of Understanding” (MOU), established between the BOR and the USGS in 2004, to facilitate sharing of data.

An Interagency Agreement between USGS and BOR was then created in 2006, to promote the distribution of geospatial datasets using an on-line web-mapping service.  This will make a Lower Colorado River Map Atlas available to the general public for visual analysis using ArcIMS software, in which the user needs only access to the Internet to have the ability to navigate the GIS data, turning layers on/off and zooming into areas of interest. 

REFERENCES

Norman, Laura M., Webb, Robert H., Gass, Leila, Yanites, Brian, Howard, Keith, Pfeifer, Ed, and Beard, L. Sue, 2004, Geospatial Analysis Of Changes In River-Channel Position And Riparian Vegetation Of The Lower Colorado River: Proceedings, The Geological Society of America Denver Annual Meeting, November 7–10, Paper No. 218-9, Denver, CO. (POSTER)

Project Background