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November 10, 2022

Title: USGS Science Support of Bi-National Efforts to Restore Riparian Ecosystems in the Colorado River Delta

Speaker(s): Patrick B. Shafroth, Volunteer-Emeritus, Fort Collins Science Center; Pamela L. Nagler, Research Physical Scientist, Southwest Biological Science Center; Eduardo Gonzalez-Sargas, Research Scientist, Colorado State University

Date: November 18th at 2:00 pm Eastern

Satellite view of the endpoint of the Colorado River.
Endpoint of the Colorado River, MexicoLess than 80 years ago, the mighty Colorado River flowed unhindered from northern Colorado through the Grand Canyon, Arizona, and Mexico before pouring into the Gulf of California. But as this NASA Earth Observatory satellite photo from September 2000 shows, irrigation and urban water needs now prevent the river from reaching its final destination. Rather, the Colorado River just disappears into the desert sands.The Colorado River can be seen in dark blue at the topmost central part of this image. The river comes to an end just south of the multicolored patchwork of farmlands in the northwestern corner of the image and then fans out at the base of the Sierra de Juarez Mountains. Only about 10 percent of all the water that flows into the Colorado River makes it into Mexico and most of that is used by the Mexican people for farming.

Summary: A treaty signed by the U.S. and Mexico in 1944, and various subsequent amendments (“Minutes”), are the basis for bi-national agreements between the two countries, including management of water in the Colorado River. One aspect of these agreements in the Colorado River delta (in Mexico, downstream of the U.S.) involves the allocation and delivery of Colorado River water to support efforts to restore riparian ecosystems. In his A Sand County Almanac (1949), Aldo Leopold famously described the Colorado River delta’s thriving ecosystems. However, by the 1960’s, combined effects of streamflow depletion and land conversion had dramatically reduced the quantity and quality of these systems and the river seldom flowed to its terminus in the Gulf of California. While some USGS involvement in the Delta began in 1998, significant effort across multiple science centers began in 2014 and continues to the present in the context of Minutes 319 and 323. In the case of both of these Minutes, some Colorado River has been allocated to support efforts to restore native riparian forests, which provide essential habitat for migratory birds. Minute 319 was focused largely on a single high or “pulse” flow in 2014 and lower flows from 2015-2017. Under Minute 323, which began in 2018 (and is scheduled to end in 2026), water deliveries are used primarily to irrigate managed restoration areas. USGS scientists led and are leading multiple efforts and are supporting others related to these restoration activities. Under Minute 319, USGS scientists conducted an array of studies related to the “pulse flow,” including surface and groundwater hydrology, dynamics of riparian vegetation, large-scale changes in vegetation “greenness” and actual evapotranspiration (ETa), and sediment transport and geomorphic change. Results of these efforts were published in a special issue of the journal, Ecological Engineering (2017) – USGS had five co-authors on eight of 17 articles in the issue and served as co-editors. Under Minute 323, primary research activities have included continued processing and analysis of remotely-sensed data to assess large-scale dynamics of vegetation and ETa in the riparian corridor, and development of several publications related to avian use of these delta habitats. Both of these foci are largely conducted in the context of assessing the effects of restoration efforts. Two key USGS activities in recent years, related to data delivery, have been to 1) deliver actionable science to end-users through the development of a searchable, remotely-sensed, vegetation greenness and ETa database, and 2) lead the development of a database system for sharing and archiving data among the Minute 323 Science and Monitoring community. This community includes myriad governmental, NGO, and University scientists and stakeholders from both sides of the border. Another significant role of USGS has been to provide technical assistance on a range of topics to our partners. In the remaining four years of Minute 323, planned activities include continuation of ongoing efforts with respect to assessing the outcomes of restoration actions on variables such as vegetation, hydrological processes (e.g., ETa), and avian ecology. New efforts include assisting restoration practitioners to improve understanding of the dynamics and influences of target restoration habitats and the importance of connectivity between habitat patches; helping develop a system to provide early warning of water stress which can negatively affect vegetation in the restoration sites; and expanding surface water-groundwater modeling efforts.