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I I I I I I I I I I I I I I I I I I I EXECUTIVE SUMMARY INTRODUCTION This report presents the results of a process to develop flow recommendations for the native fish community, including the endangered Colorado pikeminnow (Ptychocheilus lucius) and razorback sucker (Xyrauchen texanus), in the San Juan River of New Mexico, Colorado, and Utah. Flow recommendations are a major milestone of the San Juan River Basin Recovery Implementation Program (SJRIP), which was initiated in 1992 with the following two goals: 1. To conserve populations of Colorado squawfish and razorback sucker in the basin, consistent with the recovery goals established under the Endangered Species Act, 16 U.S.C. 1531 et seq. 2. To proceed with water development in the basin in compliance with federal and state laws, interstate compacts, Supreme Court decrees, and federal trust responsibilities to the Southern Utes, Ute Mountain Utes, Jicarillas, and the Navajos. Mimicry of the natural hydrograph is the foundation of the flow recommendation process for the San Juan River. Scientists have recently recognized that temporal (intra- and interannual) flow variability is necessary to create and maintain habitat and to maintain a healthy biological community in the long term. Restoring a more-natural hydrograph by mimicking the variability in flow that existed before human intervention provides the best conditions to protect natural biological variability and health. The linkages between hydrology, geomorphology, habitat, and biology were used to define mimicry in terms of flow magnitude, duration, and frequency for the runoff and base- flow periods. The flow characteristics of these linkages were compared with the statistics of the pre- Navajo Dam hydrology to assist in fine-tuning the flow recommendations. The flow recommendations require mimicry of statistical parameters of flow, based on the linkages developed and the statistical variability of the pre-dam hydrology rather than mimicry of each annual hydrograph. A 65-year-long period of record (1929 to 1993) was used to assess the relationship between water development scenarios and the ability to meet the flow recommendations. Data were gathered and analyzed during a 7 -year research period (1991 to 1997) to determine fish population and habitat responses to reregulation of Navajo Dam to mimic a natural hydrograph. The research involved quantification of several relationships, including flow/geomorphology, geomorphology/fish habitat, and flow/habitat availability relationships. The SJRIP will use an adaptive management process, along with monitoring and continued research, , to adjust the flow recommendations in the future. The ability to adaptively manage the system is SJRIP Biology Committee May 1999 S -1 Executive Summary Flow Report