The trajectory (direction of movement) of oil spilled into a river is affected not only by the river currents -- which generally take the oil downstream -- but also by the wind. If the wind blows straight down the river, the oil may travel quite far down the river before it comes in contact with either bank. But if the wind blows at an angle to the river, the oil is more likely to be blown towards one or the other riverbank.
You can see how this works by looking at two short movies showing predictions from GNOME, our oil spill trajectory model, for a small oil spill in the Columbia River estuary.
20-knot Wind from the East
In this movie, the wind is blowing in almost the same direction as the current is flowing. The oil is not blown towards either riverbank, so most of it remains on the surface and flows out the river mouth to the sea.
20-knot Wind from the Southeast
In this movie, the wind has changed direction to blow more towards the north bank of the river. Because the wind influences the movement of the oil, the oil travels a much shorter distance downstream before it contacts the north bank of the river.
More Information about Spills in Rivers
Oil Spills in Rivers: Find out why oil spills in rivers differ from spills that occur in the open ocean.