- Interaction of forces that create ocean tides and currents are complex
- Predicting future conditions requires accurate information about present and past conditions
- NOAA operates 200+ water-level stations in US waters that provide real-time data to scientists & educators
Kneel on a beautiful golden beach, reach out and make the final adjustment to your sandcastle. Sit back and admire its architectural splendor: The towering spires, the crenellated battlements. Listen blissfully as the gentle blue sea laps in the background.
This hard work deserves a rest. Retire to your towel, and take a well-earned nap. But when you wake, the tide has come in and washed your masterpiece away – was it just a dream?
No, tides are very real. To improve student knowledge of this tremendous force, the US National Ocean Service (NOS) has launched an educational initiative to track and explain tidal movements.
Tracking the tides
Ocean tides result from the gravitational attraction of the sun and the moon, but the interaction of the forces generated by each can be quite complex. The size and shape of coastlines and local weather patterns also affects tides. A standard practice for predicting future conditions is to begin with good information about the present and the past.
To amass this knowledge base, the National Oceanic and Atmospheric Administration (NOAA) manages 210 long-term, continuously-operating water level stations in the US and its territories, as well as approximately 100 short-term stations each year in support of various programs.
The National Water Level Observation Network (NWLON) has collected water level and tidal data in the US since the 1800s. Continuous records for the Presidio in San Francisco date back as far as June 30, 1854.
Historical water level stations relied on mechanical floats and a pen and ink strip chart that was retrieved by human observers once a month and mailed to headquarters for manual processing.
In contrast, modern collection stations use computers to send an audio signal down a .05-inch sounding tube and measure the interval before the reflected signal travels back to the surface. The stations collect new data every six minutes and transmit it hourly to NOAA headquarters. In stormy conditions they can be reprogrammed to transmit every six minutes.
Real-time water level information is now available to commercial navigators, recreational boaters, municipal planners, scientists, and researchers.
Students and educators can get in on the act with extensive classroom materials, including lesson plans, worksheets and assignments using easily-accessible, real time data from the collection stations.
The trouble with tides
Why all the fuss about tides? People who live in coastal areas have long found it necessary to monitor tides and tidal currents and to try to predict them. Understanding low tides prevents ships from entering harbors or navigating narrow waterways. Knowing the timing of high tide makes it safer to pass beneath bridges.
Fish populations concentrate during certain tidal currents, resulting in feast or famine for fishermen. Strong currents make ocean swimming treacherous, and beachgoers who venture onto sandbars may find their return route cut off by high tide.
Tides and currents also affect the removal of pollutants from land and the recirculation of nutrients for organisms that inhabit near-shore waters.
In other words, there’s much more than a sandcastle at stake.
Water level monitoring over long periods of time is particularly helpful in understanding the ocean’s role in world climate and climate change. NWLON analyzes sea level trends by computing changes in mean sea level using a minimum span of thirty years of observation at each location.
In addition, long-term sea level records are a good lens through which scientists can view climate change-related phenomena such as global temperature fluctuations, hydrologic cycles, glacier and ice sheet coverage, and the frequency and intensity of storms.
Putting this knowledge to use means coastal managers and engineers can adjust for the impacts of sea level rise in long-range planning. Just like the sandcastle, engineers need to know about tides and currents to ensure the safety of bridges and other coastal constructions.
Take a tour through NOS's tidal teaching materials, and maybe next time you build a castle on the beach, you’ll know how best to protect it.