A DELTA ONCE MORE: RESTORING RIPARIAN AND WETLAND HABITAT IN THE COLORADO RIVER DELTA Daniel F. Luecke Jennifer Pitt ENVIRONMENTAL DEFENSE FUND Boulder, Colorado Chelsea Congdon Boulder, Colorado Edward Glenn, Ph.D. Environmental Research Laboratory, University of Arizona Tucson, Arizona Carlos Valdés-Casillas, Ph.D. Instituto Tecnológico y de Estudios Superiores de Monterrey Guaymas, Mexico Mark Briggs Sonoran Institute Tucson, Arizona June 1999 ISBN 1-58144-356-0 © 1999 Environmental Defense Fund The Environmental Defense Fund is a leading, national, New York-based, private, non-profit, research and advocacy organization with more than 300,000 members nationwide. EDF’s staff includes scientists, economists, engineers, and attorneys who seek practical solutions to a broad range of environmental and human health problems. Copies of this report may be obtained from: EDF Publications 1875 Connecticut Avenue, NW Washington, DC 20009 ACKNOWLEDGMENTS EDF gratefully acknowledges the contributors who have generously supported its work in the Colorado River Delta region, including the Compton Foundation, the General Service Foundation, the Charles Stewart Mott Foundation, the Catto Foundation, and the Environmental Protection Agency. Thanks to Elena Chavarria for her intelligent translation of the executive summary. In addition, credit is due to Osvel Hinojosa, Yamilett Carrillo, Jaqueline Garcia and Francisco Zamora for their contributions to research in the Colorado River Delta. ABOUT THE AUTHORS: Daniel F. Luecke is an environmental scientist and Edward Glenn is a professor in the Soil, Water, and regional director with the Environmental Defense Environmental Science Department at the University Fund in Boulder, Colorado. Over the past two of Arizona. He has studied the vegetation and water decades he has been involved in a number of river- quality of the delta in collaboration with Mexican ine and aquatic habitat protection projects. scientists over the past decade. Jennifer Pitt is a senior resource analyst with the Carlos Valdés-Casillas is the director of the Center Environmental Defense Fund in Boulder, Colorado. for Conservation of Natural Resources (CECARENA), From 1994 to 1998 she worked on river restoration and head of research of the Instituto Tecnológico y for the National Park Service and American Heritage de Estudios Superiores de Monterrey (ITESM), Rivers. Campus Guaymas. He has published several reports on assessment and planning of coastal areas in Chelsea Congdon was a senior resource analyst with Mexico, in particular on the Sea of Cortez. the Environmental Defense Fund for 11 years. From 1995 to 1998 she worked in EDFs Rocky Mountain Mark Briggs is the director of research at the Sonoran office, leading the organizations efforts in the Institute, Tucson, Arizona. His area of focus is on Colorado River delta. She continues to work on delta evaluating the health of riparian ecosystems and restoration as a consultant and documentary film developing strategies for improving their overall eco- producer. logic condition. iii EXECUTIVE SUMMARY Historically, the Colorado River fed one of the deserve greater consideration in the allocation greatest desert estuaries in the world. The of Colorado River resources, the deltas mini- Colorados delta consisted of vast riparian, mum requirements are surprisingly modest. freshwater, brackish, and tidal wetlands that This report outlines the deltas natural and covered 1,930,000 acres (780,000 ha) and cultural history, documents recent scientific supported a legendary richness of plant, bird, findings about the deltas partial recovery, and marine life. Today, conditions are changed. reviews its current political context, and makes Decades of dam construction and water recommendations for securing, assuring, and diversions in the United States and Mexico have managing existing flows to further benefit and reduced the delta to a remnant system of small sustain the deltas remnant wetland ecosystems. wetlands and brackish mudflats. The authors assessed habitat values in the Recently, however, the delta has begun to deltas vegetated riparian areas and wetlands, make a comeback. In the last two decades, and found relatively large areas of dense, floodwater, releases from reservoirs in the woody vegetation capable of supporting signifi- United States, agricultural return flows from cant bird populations. In addition, the authors both countries, and municipal wastewater from measured the quantity and rate of water flows Mexico have proved beneficial. Although flood needed to sustain delta vegetation, and found flows are extremely unreliable and irregular, that annual flows of 32,000 acre-feet (4 x 107 m3), and wastewater is high in salinity and pollut- supplemented by periodic (once every four ants, this water has begun to restore some areas years on average) flood flows of 260,000 of the delta. Current conditions have allowed acre-feet (3.2 x 108 m3), should suffice. Research wetlands to flourish on about 150,000 acres documenting flows needed to support the (60,000 ha). fisheries of the delta and the near-shore marine The authors believe that key areas of the delta environment of the Gulf of California has not might be saved through more efficient use of yet been conducted. water that now flows into the delta. This could Finally, the authors outline recommendations be accomplished without adverse effects on to manage existing flows for the benefit of delta other Colorado basin water users. While ecosystems; change international institutions demand for water by irrigators, cities, and other and agreements to support delta ecosystems; important constituencies makes it unlikely that establish market mechanisms and funding a natural flow regime can be restored to the sources for delta preservation; increase public delta, deliberate management of existing water participation; conduct further research; and resources, such as agricultural drainage, waste- implement site-specific restoration. water, and floodwater, could make a significant difference. Although the deltas ecosystems iv RESUMEN EJECUTIVO Por tiempos inmemorables, el río Colorado mejores consideraciones en la distribución de alimentó uno de los mayores estuarios recursos del Río Colorado, los requerimientos desérticos del mundo. El delta del Colorado mínimos del delta son sorprendentemente consistía en más de 781,060 ha. (1,930,000 acres) modestos. cubiertas por bastos humedales riparios de agua Este reporte describe la historia natural y dulce, agua salobre y de mareas, que sustentaba cultural del delta, documenta los hallazgos una riqueza legendaria de plantas, aves y vida científicos mas recientes referentes a la marina. Hoy las condiciones han cambiado; recuperación parcial del delta, revisa el contexto décadas de construcción de presas y desviación político actual y ofrece recomendaciones para de agua en Estados Unidos y México, han asegurar y orientar el manejo de los flujos reducido el delta a un sistema remanente de existentes hacia el beneficio y sustentabilidad pequeños humedales y lodazales salobres. de los ecosistemas de humedales remanentes Recientemente, sin embargo, el delta ha iniciado del delta. su regreso. En las dos últimas décadas, la Los autores evaluaron los valores del hábitat liberación de flujos de agua de las presas de en la vegetación riparia del delta y encontraron Estados Unidos, las aguas residuales agrícolas áreas relativamente extensas de densa de ambos países y el agua de desecho munici- vegetación de galería y boscosa capaz de pal de México, han probado ser benéficas. A soportar poblaciones significativas de aves. Del pesar de que los flujos de inundación resultan mismo modo, los autores realizaron mediciones ser extremadamente aleatorios e irregulares, y sobre la cantidad y tasa de flujos de agua que las aguas residuales tienen elevada requeridos para soportar la vegetación del delta salinidad y contaminación, esta agua ha y encontraron que flujos anuales de 4 x 107 m3 empezado a restaurar algunas áreas del delta. (32,000 acres-pie), acrecentados por flujos de Las condiciones actuales han permitido el inundación de 3.2 x 108 m3 (260,000 acres-pie) establecimiento de 54,725 ha. (150,000 acres) de cada 4 años en promedio , será suficiente. Aun humedales. no se ha llevado a cabo la investigacion para Los autores confían en que ciertas áreas del delta establecer los flujos necesarios para las podrían ser salvadas mediante un uso mas pesquerias en el delta y en el litoral del Golfo eficiente del agua que fluye ahora a través del de California. él. Esto puede lograrse sin efectos adversos Finalmente, los autores enlistan reco- sobre los otros usos del agua del cauce del mendaciones para el manejo del flujo existente Colorado. Dado que la demanda de agua para para beneficio de los ecosistemas del delta: irrigación, ciudades y otros usuarios de cambiar instituciones y acuerdos inter- importancia, hace remota la posibilidad de que nacionales para apoyar los ecosistemas del un régimen de flujo natural pueda restaurarse delta, establecer mecanismos de mercadotecnia para el delta, el manejo deliberado de los y recaudar recursos para la preservación del recursos hidráulicos, como drenes agrícolas, delta; incrementar la participación pública, aguas residuales y flujos de inundación, avanzar la investigación e implementar podrían lograr una diferencia significativa. A restauración en sitios específicos. pesar de que los ecosistemas del delta merecen v TABLE OF CONTENTS EXECUTIVE SUMMARY.......................................................................................................................................