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P -2- This report leans heavily on the wort: of Annear (1980) which is included here in its unaltered thesis form as Appendix I. An effort is made in the following "Synthesis" section to discuss Annear's findings relative to the above stated objectives. The "Synthesis" also explores additional data not included in Appendix I. SYNTHESIS The Yampa and Green Rivers immediately above their confluence are both fifth order streams, draining geologically similar watersheds which in turn have had historically similar use patterns. The main differences between the two streams are discerned with a comparison of their flows (Table 1). Prior to the closure of the Flaming Gorge Dam in 1962, the mean annual monthly flows for the fifth order Green and Yampa Rivers were essentially the same, 2133 and 2223 CFS respectively. Differences in the timing for the peak flows (late for the Yampa) and mean monthly variations (greater for the Yampa) also existed. After closure the flows in the Green were moderated even further and are now with substantially less variation than the Yampa. Also apparent in Table 1 is a difference in the flow rates between preclosure and postclosure dates for the Yampa River. This is allayed to a small but significant increase in irrigation use of the Yampa and Little Snake Rivers. The concentration of several chemical parameters also increased during this period (Table 2) as did the conductivity (relat ed to total disolved solids). The pH also increased as one might expect with an increase in the basic ionic components (Table 2). No pre closure data existed for the Green River but since mean flow rates did not change materially after closure there is little reason to believe that gross water qaulity was much different from what it is now after closure (Table 2). Mean monthly temperatures peaked in July and August at 20 -20 0C. in both rivers prior to dam closure and reached a low of 0 - 1 0c during the period December to February. After closure, however, the temperatures in the Green River moderated at a much lower level above the confluence with the Yampa varying but from 4 to 11 0C. Below the confluence little difference existed before or after closure. (Appendix I, p 35). 16