Tides, Breakers, and Fetches

Flooding on Gate 5 Road during a 2019 winter storm | photo and post by Larry Clinton

This is the third installment of a research paper on the microclimates of Richardson Bay by Yellow Ferry Resident Richard Pavek.

Sooner or later, everyone who lives on the water acquires a tide chart thinking it will forecast the high and low tides. But it doesn’t. While NOAA scientists can calculate the timing of the tides from the Moon and Sun’s relative locations and the gravitational pull on the Earth, they cannot predict the actual tide’s highs and lows.

Forecast Tides and Actual Tides. The highs and lows on tide charts are approximations, calculated by averaging the highs and lows for the past ten years and projecting them forward for the coming year(s). Overriding this baseline of highs and lows are the floodwaters from rainstorms and wind-driven bay currents that form the actual tides.

High Tide (High Water)—There are two highs per day; one is higher than the other. (Highest High Tide and Lowest High Tide—the highest is the one to worry about).

Low Tide (Low Water)—There are two per day. Of little concern to those who park on the shore.

Seasonal Tide Levels in the Northern latitudes are higher in winter than summer.

Rainfall Swollen Tides are High Tides inflated by the drenching rains of atmospheric rivers.

Mean Sea Level (MSL, often shortened to sea level) is an average surface level from which heights such as elevation may be measured.

Global Sea Level refers to the average height of all the Earth’s ocean basins. Global Sea Level Rise refers to the average global sea level increase. ‘Local sea level’ refers to the water’s height measured along the coast relative to a specific point on land. Tide stations measure the local sea level as well as the tides.

Breakers—Tides that break upon a beach every 10 seconds to a minute. These tides are caused by sea-level disturbances far out in the Pacific Ocean. Additionally, various circulating currents of seawater can create strong winds directed towards the land, which will bring water up onto the beach. As this water travels towards the beach from deep to shallow water, its amplitude (height) increases until it finally ‘breaks’ as a full-fledged breaker suitable for surfing.

Fetches—The distance traveled by winds or waves without obstruction.