Figure 10 . Difference between the Snake and Salmon Rivers, 1991-1997. Positive numbers indicate the Snake River is warmer. Figure 11 . Temperature difference between RM 192 and RM 180, 1991-1997.
Positive values indicate river warming.
To quantitatively understand the Snake River heat budget and characterize the effect of flow from Hells Canyon Dam on the downstream water temperature, a simplified heat budget model can be applied. The model considers atmospheric heating and cooling, and mixing of temperatures from the tributaries that flow into the Snake River. Figure 12 illustrates a simplified diagram of a river with atmospheric heat exchange as water flows downstream between points a and b . At point c a tributary with a different temperature enters the river. In the short reach from b to d , the primary temperature change is the result of the mixing of water from the tributary at c .