Yaquina Estuary receives freshwater inflow primarily from two tributaries, the Yaquina 
River and Big Elk Creek, which have similarly sized drainage areas and contribute 
approximately equally to freshwater inflow (Figure 2.2; State Water Resources Board, 1965). 
The long-term median freshwater input to Yaquina Estuary is 7.5 m s' . There is a strong 
seasonal pattern in freshwater input to the Yaquina Estuary (Figure 2.3). During the months of 
November through April, the Oregon coast receives high precipitation and the estuary is river 
dominated. Beginning in May and continuing through October, there is a decline in the riverine 
freshwater inflow and the estuary switches from riverine to marine dominance. For this 
document, we defined the wet season (November - April) as months when the median monthly 
discharge exceeds the long-term median annual discharge and the dry season (May- October) as 
months when the median monthly discharge is less than the long-term median. The estuary is 
well mixed under low flow conditions, and partially- to well- mixed during winter high inflow 
conditions (Burt and McAlister, 1959; Kulm and Byrne, 1966). The flushing time of the estuary 
during the dry season varies from 1 day near the mouth to 9 days in the upstream portions (Choi, 
1975). 
Figure 2.2 Map of watershed of the Yaquina Estuary, showing the two primary tributaries 
(Yaquina River and Big Elk Creek). 
7 
