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Photo 3. Aerial view of the Colorado River delta, near where the Colorado meets the upper Gulf of California These floods are significant, sustaining the delta's ecosystems through the periodic inundation of its riparian areas and wetlands. Satellite images show a marked decline in summer vegetation during five dry years from 1988 to 1992. Floods in 1993 were followed by three more dry years, but in 1997 scientists observed that midstory trees that appeared to have germinated in 1993 dominated many parts of the delta (Glenn, 1998b). These trees survived three years without river flows. This and other evidence lead researchers to be- lieve that flood flows at three- or four-year intervals could maintain vegetation. These floods also could help sustain upper Gulf shrimp fisheries and other marine species dependent on the delta. Future research on Gulf aquatic species may yield more specific information concerning their dependence on freshwater flows from the delta. Given the apparent importance of floods, one possible way to support delta ecosystems would be to deliber- ately manage flood releases for maximum benefit. Water management agreements on the Colorado River include provisions for allocating water under shortage and surplus flow conditions.26 These agreements could be revised to ensure that a portion of surplus flood flows are stored for, or delivered to, water-dependent ecosystems in amounts and rates, and at times, that would be most beneficial. 25 It should be noted that annual flow averages and flood release figures do not always reflect the amount of overbank flooding-the inundation of riparian lands-that occurs in the delta. This is more accurately reflected in rate of flow as measured in cubic feet or meters per second. 26 The U.S. Bureau of Reclamation, the agency responsible for management of the Colorado River dams and flows, reports expected flow conditions to Mexico through the International Boundary and Water Commission (Johnson, 1999). 14