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, , Application of IFG's lnstream Water Temperature Model in the Upper Colorado River "; The Colorado River below Glen Canyon dam previousiy supponed large populations of squa.....'-lSh and chub: now, none are present (Minckley and Deacon. 1968). Chub, however, have been observed in the tail waters of the Linie Colorado River beiore these ......aters mix with the cold main. stem waters. The hypolimnentic (deep water) release from the reser. voir subseauent to its closure nrovides relativel\' cold water below Gl~ Canyon dam. Fo; example. according to pub- lisl\ed water quality data for the USGS pge at Lees Ferry, which is located ~6 kilometers downstream from the dam. the mean July temperature in 1973 was 8.SoC ro.s, Geo- logical Survey, 1973). The cold thermal regime induced by the reservoir persists far downstream because there are no ~arge tributaries to ameliorate these very cold release waters, \ The resulting lack of successful spawning has eliminated \ squawfJSh and chub populatiom in these cold water reaches ! (MWer. er 1lI.., 198~). ~ Below Aaming Gor~ resenoir, a similar situation exists. No squawfish or chub are currently found in the Green River between the dam and the con1luence with the Yampa River. a distance of 104 kilometers. The Yampa is an un. conuaIled moutary that contributes more than one.third of the Green River flow. Both fISh mec:ies still inhabit the Yampa and are also found in the G~ below the Yampa con1luence (Holden and Crist, 1981 ). Water temperature is sufficient to explain the absence of squawfish and chub in the Green above the confluence. To comply with the Endan~d Species Act, future developers in the UCRB will be required to eDSUre that pro- posed' projects maintain necessary water temperatures. Be- cause the inmeam water temperature model can predict dOWDStream water temperatures under various conditions ~ ~= reservoir release temperatures and dischal'l!e5. the m could be used to analyze proposed projectS and to sugest means of mitigating, or even enhancing, aquatic habitaL ) MODEL APPUCATIONS 'Ibe impacts of reservoir release temperatures and dis- charps. or any other form of diversion or augmentation. on dOWllStream water temperatures can be simulated by the model. The effects of otherwise natum flows can be in- cluded in the simulation. This paper will present twO ap- plications of interest to water resource planners and fIShery manaaerSo Two outnut disnlavs are useflJ! to visualize these applications - a. longitudinal temperature profIle aJ1d a temperature versus site dischar e curve. The fust example UStrates an app lCation using the longitudinal profile Out- put display. This displa~' locates the river reaches of suitable spawning habitat for squawflSh. The second example illus. trates an application using the temperature discharge output display. it is used TO determine site discharge mnges neces. sary to maint:lin suitable temperature for squa.....iish and .:hub spawning. The fU'St example demonstrates do.....nstream tempera. ture changes due to various reservoir release temperatures. Output was obtained for a given reservoir release discharge and a single constant set of hydrometeorological condi. tions, The simulated water temperatures include the effeCts oi all additional normal flows in the stream network. The water temperatures are plotted versus river location for each release temperature (Figure :). The plots are called longitu- dinal temperature promes, In this example, only the profIle from the Yampa syn- thetic gage Oocation of assumed reservw) down to the Ouray Study site are shown. Normal July hydrometeoro- logical conditions were used. Each profIle is for the specie fied reservoir release temperature varying from 4-ISoC and one at 19.400C. The latter prome is the normal July water temperature at the Yampa synthetic gage and. therefore. represents existing normal July conditions. The normal July diurnal fluctuation is less than =2.00C at Ouray. Suitable squawfish spawning temperatures are superim- posed on the promes to clearly see the resulting river reaches of suitable spawning temperature habitat, Also added is substrate suitability, The river reach below Split Mountain contains a sand substrate which is unsuitable for spawning (Prewitt, eu1.., 1981). This example shows that assumed reservoir release tern. peratures between 4 and lSoC would not provide the mini- mal spawning temperature threshold for squawfish at any suitable downstream location between the assumed,reser. voir (Yampa synthetic gage) and Split Mountain. Only reo leases approaching existing conditions (19.400C) ~ to ensure proper spawning temperatures in some of the reo maining known spawning reaches betWeen these two loca- tions. The Green River between the Yampa-Green con- fluence and Split Mountain provi~es only marginal spawn- ing habitat (Joseph. et 1lI.., 1977). A validation check was made at interior gages within the network. Measured water temperawres (smoothed by the respective pgr's r~ession model) w.ge comlJared tn wlues that were independently e!.edic~d Q)' the p~'5ica1 process ~odel. The difference between the predicted and measured \'Ilues is the validation check. The result of the vaiidation check at Jensen gage, which is located between the Yampa. Green confluence and the Ouray stUdy site. was +O.S:oC for the normal July hydrometeorological conditions, Ob- viously, this prediction is the uncalibrated \'alue: the model could easily be calibrated to completely eliminate the dif- ference. The above analysis was made using historical data for the operation of Aaming Gorge. The historical normal July ,~ temperature release is 6.51 oC. Recentl\', a variable le~ selective withdrawl operatinsr: s:heme has been implement~d at Aaminsr: Gorsr:e. The new normal Juh' release temnera. ture is 11.110C Wemer. er ai,. 1981).'This results in a Green River water te-mperature of 19.5oC inunediately be. low its confluence with the Yampa for existing normal J..iy hy:irometeorologica: conditions. Therefore. the Green Ri\'e~