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4. CONCLUSIONS The general objective of this investigation of two known Colorado squawfish spawning sites in the lower Yampa Canyon, Mathers Hole (AM 17.5) and Cleopatras Couch (AM 16.5) was to build on previous work to identify the dynamics of squawfish spawning habitat formation that was commenced by a multi-disciplinary team of biologists, geomorphologists and hydraulic engineers in 1991. The earlier work at C1eopatras Couch and the Alternate Spawning Bar (RM 18.5) was used to develop a physical process-biological response model for spawning habitat formation, that had limited validation (Harvey et aI., 1991, 1993; Mussetter et aI., 1992). Fish capture data in 1992 at Mathers Hole and C1eopatras Couch on the Yampa Aiver at a discharge of about 600 cfs, and a long history of fISh capture at the head of Gray Canyon on the Green Aiver provided the impetus to further test the essential elements of the PAM. The specific objectives of the 1993 field investigation of the lower Yampa Canyon sites at Mathers Hole and C1eopatras Couch were to: 1. Test the PAM at a known spawning site where the physical conditions are somewhat different to those where the model was initially developed, 2. Evaluate whether the observed patterns of squawfish congregation at different locations during the spawning period can be related to physically-based changes at the individual spawning bars during the recessional flows, 3. Attempt to develop physically-based criteria for locating other potential Colorado squawfish spawning locations for subsequent testing by biologists, 4. Begin to address the question of the required frequency of bar-forming discharges at the spawning locations. Based on the data collected during the 1993 field work and subsequent analyses ofthese data and others derived from previous work, the following conclusions can be drawn from this investigation. 1. The geomorphic and hydraulic analyses conducted at the Mathers Hole spawning bar indicate that this location meets each of the three sets of criteria (macroscale, meesoscale and microscale) required by the PAM for formation of squawfish spawning habitat. 2. On a macroscale level the sharp bend in the canyon and bedrock-induced valley constriction cause backwater conditions that are responsible for bar formation. The flows are confined by the left valley wall and the strath terrace on the right side of the channel, up to and including, the flood of record (32,300 cfs). 4.1 Resource Consultants & Engineers, Inc.