as Brownlee and a natural river-lake system is the 

 depth at wliich the water is discharged. Flows 

 fi'om a reservoir are usually discharged at depth, 

 whereas flows from a lake are discharged from the 

 surface. At Bi-ownlee, the turbine intake is 36.6 m. 

 below normal pool level. Tlie spillway discharges 

 from the surface and from a depth of 35.4 m. 

 Fluctuation in water level is considerable during 

 late fall and winter; the reservoir is lowered as 

 much as 32. S m., depending on forecasts of ex- 

 pected spring runotf. The fluctuations lead to ter- 

 raced mudbanks that are unproductive areas. Av- 

 erage vohunes of water from the Snake River at 

 Weiser, Idaho, range from 255 c.m.s. ( cubic meters 

 per second) in late summer to 1,132 c.m.s. in the 

 spring. Maximum rate of flow during the studj' 

 period was about 1,416 c.m.s.^ 



METHODS 



Sampling stations were establisiied throughout 

 Brownlee Reservoir and at certain locations rip- 

 stream and downstream from the reservoir to 

 measure physical and chemical properties of its 

 water. Temperature, dissolved oxygen concentra- 

 tion, and current were the principal factors 

 studied. The location of sampling stations and 

 the techniques and equipment iised are described. 



SAMPLING LOCATIONS AND TECHNIQUES 



We established sampling stations .throughout 

 the resei'voir and at certain locations upstream 

 and downstream from it (fig. 1). Twelve main sta- 

 tions were spaced about 6 km. ajiart on the axis 

 of the reservoir. They extended from 1 to 69 km. 

 above the dam. Occasional sanqjling was done be- 

 tween these main stations. Additional stations 

 along the Snake River included sites on State 

 highway 30 at the bridge in Weiser, State highway 

 71 on interstate bridge below Brownlee Dam, and 

 on the catwalk below the Oxbow and Brownlee 

 power plants. Other stations were at Eagle Creek 

 (on the Powder River) and at five places in the 

 Powder River ann of Brownlee Reservoir. '\>'ater 

 samples were also collected at fish-trapping sites 

 throughout the reservoir during the periods of 

 migration by salmon. 



All permanent stations were sampled once every 

 2 weeks durine summer stratification of the water 



in 1062 and once a month in winter and early 

 spring after turnover of the water in 1963-64. 

 Permanent stations were marked by Styrofoam ^ 

 buoys anchored to concrete blocks to assure sam- 

 pling at the same location each period. 



Four sets of diurnal observations were made in 

 addition to the routine sampling. These observa- 

 tions covered either a 24- or 48-hour period; sam- 

 ples were taken every 3 to 6 hours. 



To secure temperature profiles from top to bot- 

 tom and define the epilimnion, thermocline, and 

 hypolinniion when present, depth and conductivity 

 readings were recorded with each temperature 

 change of 0.55° C. as read from a Whitney therm- 

 istor and conductivity meter. The thermistor was 

 calibrated daily with a certified laboratory ther- 

 mometer and checked periodically at various 

 depths with a mercury reversing thermometer. The 

 conductivity meter was calibrated daily. 



During periods of stratification, water samples 

 were taken in 2i4-liter plastic Van Dorn bottles to 

 determine dissolved oxygen and other character- 

 istics in each of the three water masses. Before and 

 after stratification, sampling was from the sur- 

 face to the bottom at intervals up to 15 m. Sam- 

 ples were kept in an insulated cooler to minimize 

 chemical changes that might be caused by in- 

 creasing temperatui-e. Dissolved oxygen was de- 

 termined by the unmodified Winkler method 

 (American Public Health Association, 1960) ; a 

 second sulisample was drawn and placed in a 

 l>lastic bottle for later determination of free carbon 

 dioxide, sulphate, turbidity, total and phenol- 

 phthalein alkalinity, and pH. Duplicate samples 

 from some of the same casts were collected at least 

 once every sampling day to check accuracy of all 

 deteiMninations. 



Daily maximum and minimum air tempera- 

 tures, precipitation, and wind direction and ve- 

 locity were recorded at two stations. IVIeteorologi- 

 cal data were received from the weather station 

 operated by Radio Station KWEI at Weiser, 

 Idaho. A second weather station was established 

 near station 14 on the we,st side of the reservoir. 



A temperature pi-ofile was determined by taking 

 the temperature from top to bottom and recording 

 the depth at every temperature change of 1° F. 



1 A flow of 2.209 c.m.K, wa.s recorded in December 1964 (after 

 the study ended) . 



-' Trade names referred to in this jniblication do not imply 

 endorsement of commercial products by the Bureau of Com- 

 mercial Fisheries. 



LIMNOLOGY OF BROWNLEE RESERVOIR 



297 



