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King Tides: Look out for coastal flooding

King tides are becoming a royal pain in some coastal areas, where they bring seawater flooding into streets and parking lots. King tides will occur along the Atlantic coast of the US during the first week of November 2017.

What causes tides?

The gravitational pulls of the sun and moon cause tides. The orbits of the sun and moon are elliptical–more oval than circular. This means that as they rotate around the earth, their relative distances from the planet vary.  The closer they are to the earth, the stronger their gravitational pulls. The ocean covers more than 70% of the earth’s surface. The gravitational pulls of the sun and moon create long-period waves in the ocean. We observe these long-period waves as tides. When the sun and moon are in line with each other, their gravitational pulls act together on the earth. This is when we see our more extreme tidal ranges (higher high and lower low tides.) These usually occur with new and/or full moons. We refer to these tides as “spring tides,” regardless of the time of year in which they occur

What are king tides?

A few times a year, the spring tides will be exceptionally high. Commonly called “king tides,” these perigean spring tides are created by a new or full moon that happens to be at its closest point to the earth.  In recent years, many coastal cities have found that their streets and parking lots flood during king tides, even on sunny, dry days. In many places, sea level has risen to a point where these king tides result in seawater flowing up pipes that were intended to drain rainfall from the land. 

Global sea level has risen and fallen over geologic time scales. Current rates of sea level rise are increasing, but our built infrastructure in coastal Florida is generally not changing in elevation. This provides a challenge for drainage. When king tides coincide with storms, flooding can be extreme, as the rainwater cannot drain through pipes that are already full with seawater.

Citizen scientists are encouraged to take photographs during king tides and submit them to the King Tides Project International. The goal of this project is to use images of current day king tides to help people visualize  what “normal” water levels may be like in future years.

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