Around the Water Cooler: Tour of a King Tide

By Chris Janousek, PhD

Video taken during a king tide event shows a variety of tidal habitats in a forested estuarine valley in the Pacific Northwest. Marshes and rarer tidal swamp and scrub-shrub wetlands are shown. (Note: the video contains only background sounds; no narration or closed captions are included.)

For many years, one of my favorite activities as a marine scientist has been catching the early morning low tides along the rocky shores of the Pacific coast. The crisp salty air and the almost overwhelming diversity of intertidal marine life (not the 4 or 5 AM alarm clock) would inevitably make me glad I made the trip.

At EPA, my research has focused on the other end of the tidal range—the very highest parts of the intertidal zone where salt marshes and tidal swamps create a complex transition zone between truly terrestrial ecosystems and marine habitats like seagrass meadows. With other scientists at EPA’s Western Ecology Division lab, my work focuses on potential sea-level rise effects on coastal wetlands. Integral to understanding sea-level rise is studying high tide events.

Depending on location, North American coastlines have 1-2 high and 1-2 low tides per day. The most extreme high and low tides occur twice a month when the sun and moon are aligned linearly with the Earth. Tidal amplitudes also vary seasonally.

In the Pacific Northwest, the highest tides occur in the winter and can be up to a half meter higher than summer high tides. These are the king tides. In December 2012, we caught one of this winter’s king tides by boat while collecting water quality data in a tributary to one of Oregon’s largest coastal estuaries.

High water levels can be stressful to wetland organisms and humans alike. For organisms more adapted to life on dry land – plants and insects, for example – flooding may bring salt water, reduce soil oxygen and displace animals.

Excessive water levels also threaten developed land. The presence of wetlands in the high intertidal zone, however, creates a natural buffer protecting coastlines from damage by attenuating incoming wave energy. It is also during high tides that inorganic sediments are trapped by wetland vegetation, a process that helps these habitats maintain their elevation. Protecting and restoring such natural buffers along our coastlines may be especially valuable when high tides coincide with storm surges.

Data from both satellites and tide gauges show that sea-level has been gradually rising over the last several decades in step with other changes to the global climate. The magnitude of future sea-level change is still uncertain, but rising seas and king tides will continue to shape America’s coastal communities – both biological and human built.

About the Author: Chris Janousek, PhD is a coastal ecologist at EPA’s Western Ecology Division.

To learn more:

NOAA information about tides

Recent on-line scientific paper on vegetation’s role in attenuating coastal wave energy

EPA information on Sea Level Rise as a climate change indicator

Editor's Note: The views expressed here are intended to explain EPA policy. They do not change anyone's rights or obligations. You may share this post. However, please do not change the title or the content, or remove EPA’s identity as the author. If you do make substantive changes, please do not attribute the edited title or content to EPA or the author.

EPA's official web site is Some links on this page may redirect users from the EPA website to specific content on a non-EPA, third-party site. In doing so, EPA is directing you only to the specific content referenced at the time of publication, not to any other content that may appear on the same webpage or elsewhere on the third-party site, or be added at a later date.

EPA is providing this link for informational purposes only. EPA cannot attest to the accuracy of non-EPA information provided by any third-party sites or any other linked site. EPA does not endorse any non-government websites, companies, internet applications or any policies or information expressed therein.