CogKnoSys

Knowledge you can walk. Read the idea below, then step up to the general, across to peers or down to the specific.

Physical

Columbia River Tides

Columbia River tides are the regular rise and fall of water, driven mainly by the Moon and Sun, that reaches up the Columbia as far as Bonneville Dam.

Learn, discuss, create, buy or invest

The idea

Tides are the regular rise and fall of sea level, caused mainly by the pull of gravity from the Moon and the Sun. Along ocean coastlines, these tides rise and fall approximately twice a day, following a predictable rhythm. When the water stops rising, it has reached high tide, and when it stops falling, it has reached low tide. Between those two points, the rising water is known as the flood tide, and the falling water that follows is known as the ebb tide.

Approximately twice a month, near the new moon and full moon, the Sun, Moon and Earth form a line, and the Sun's pull adds to the Moon's. Then the tide's range is at its maximum, and this is called a spring tide. When the Moon is at first or third quarter, the Sun partly cancels the Moon's pull, so the range is smallest; this is a neap tide.

On the Columbia, tides push far upriver, and changes in water level from the tide can still be recorded as far inland as Bonneville Dam. Many river mouths, like the Columbia's, have a shallow bar at the entrance that can keep deep boats out at low tide. Because of this, pilots and sailors carefully plan their river crossings around the predicted times of high and low water.

Check yourself

Question 1 of 3

How often do ocean tides typically rise and fall?

Pick one. The first pick counts.

Composition

what it's made of

  • High tide — The highest water level in each cycle, reached when the water stops rising.
  • Low tide — The lowest water level in each cycle, reached when the water stops falling.
  • Slack water — The moment the tidal current stops before it turns and flows the other way.
  • Spring and neap tides — The largest and smallest tidal ranges, which take turns in a two-week cycle.

Connection

how it relates

Under Columbia River Estuary

In place

  1. Bonneville Damstrength 70 of 100

    Tidal changes in the Columbia's water level can be recorded as far inland as Bonneville Dam.

Cause and effect

  1. Ocean Currentsstrength 60 of 100

    Tides produce back-and-forth currents known as tidal currents.

  2. Earth Systemsstrength 50 of 100

    Tidal forces act on the entire Earth system, even moving the solid crust slightly.

Related

  1. Circular Motionstrength 40 of 100

    Tides come partly from the orbital motion of the Earth and Moon around each other.

Change

how and why it evolves

Past
In 1788 fur trader John Meares could not get his ship across the rough breakers at the Columbia's bar.
Now
Jetty building, diking and dredging have reduced the estuary's tidal prism and tidal mixing. Restoration work has reopened some cut-off swamps, so tidal waters can flow in and out of them again.
Next
These tides will likely keep following the Moon and Sun, while restoration work reopens more marshes to tidal water.

Knowledge you can walk. Read the idea, then step up, across or down.

Columbia River Tides

Columbia River tides are the regular rise and fall of water, driven mainly by the Moon and Sun, that reaches up the Columbia as far as Bonneville Dam.

Learn, discuss, create, buy or invest

The idea

Tides are the regular rise and fall of sea level, caused mainly by the pull of gravity from the Moon and the Sun. Along ocean coastlines, these tides rise and fall approximately twice a day, following a predictable rhythm. When the water stops rising, it has reached high tide, and when it stops falling, it has reached low tide. Between those two points, the rising water is known as the flood tide, and the falling water that follows is known as the ebb tide.

Approximately twice a month, near the new moon and full moon, the Sun, Moon and Earth form a line, and the Sun's pull adds to the Moon's. Then the tide's range is at its maximum, and this is called a spring tide. When the Moon is at first or third quarter, the Sun partly cancels the Moon's pull, so the range is smallest; this is a neap tide.

On the Columbia, tides push far upriver, and changes in water level from the tide can still be recorded as far inland as Bonneville Dam. Many river mouths, like the Columbia's, have a shallow bar at the entrance that can keep deep boats out at low tide. Because of this, pilots and sailors carefully plan their river crossings around the predicted times of high and low water.

Check yourself

3 quick questions, instant feedback.