Th© general run-off pattern over the entire Trinity drainage 

 varies somewhat from that recorded at Lewiston. The spring run-off 

 peak at Burnt Ranch occurs a month earlier than the peak at Lewiston 

 (Figure 3) • Inflow from many small tributaries which drain an area 

 with little snow accumulation contributes most of the earlier run-off 

 at that point. River flow at Hoopa, including the inflow from New River 

 and the extensive South Fork drainage, reaches a spring run-off peak in 

 March, two months earlier than the peak at Lewiston* 



River Temperatures 



River temperatures at Lewiston were recorded daily from November 

 1942 through July 1946 (Tables 2-5 and Figure 4). Temperatures were 

 taken with a hand thermometer three times each day, at 8 a.m., 12 noon, 

 and at 5 p.m., until January 1946. Following that date, continuous 

 temperatures were recorded by a thermograph. During most of the year, 

 the river reached its maximum temperature at about 5 p.m., and its 

 minimum at 8 a.m.; consequently, temperatures taken by hend thermometer 

 at these hours closely approximate the extremes. Average daily tem- 

 peratures after January 1945 were computed from thermograph records 

 by tftking the mean of temperature readings at two-hour intervals 

 during a 24-hour period. 



Trinity River is warmest during July and August when spring and 

 summer salmon are holding over in the main river. The maximum water 

 temperatures and dates of occurrence for years of record are as follows : 

 78*^., on August 13, 1943; 81**F., on July 24 and 27, 1944; and 83°F,, on 

 July 27, 1945» Temperature records were not complete enough in 1946 to 

 show the highest temperature with certainty, but a high of 80. 5*^., was 

 reached on July 22, 1946. The maximum temperature recorded for 1943 

 may not be the true peak temperature for that year, as it was taken from 

 partial records made during August and September. A temperature of 

 80*'F., or higher was recorded on 9 days during the sionmer of 1944 and 

 27 days during the svomner of 1945. As a result of experience gained at 

 Deer Creek Station on Sacramento River, California (Moffett, 1949), 

 80**F., is considered lethal or near lethal for king salmon. The same 

 species is able to survive when surface temperatures are ahove 80°F., in 

 Trinity River by remaining in the cooler waters of deep holes along the 

 river. In August 1944, water at depths over 8 feet in one of these 

 large holes was 7t'., cooler than surface water* 



The daily temperature range is of interest when considering the 

 effect of majcima as lethal agents. To illustrate this range In Tt-inity 

 River during summer, the hourly record for July 27, 1945, is presented* 



