Coastal Shifts: Measuring the Tidal Range

If you measure the water level at its highest point and then at its lowest point, then the vertical gap between those measurements represents the total change. If that change is measured in feet or meters, then it is defined as the tidal range.

If the high tide is 12 feet and the low tide is 2 feet, then 12 minus 2 equals 10. If 10 is the difference in height, then it is the tidal range.

If a large amount of water enters a wide opening and is pushed into a smaller, narrower area, then the water has nowhere to go but up. If the water level rises higher as a result, then the bay experiences an increased tidal range.

If the water level in this specific bay can rise and fall by as much as 50 feet in a single day, then it represents the largest difference recorded on Earth. If this is the maximum recorded difference, then it is the highest tidal range.

If water must physically move through or around obstacles, then the shape and depth of the land will change the water's height. If the body of water is large, it responds more to gravity; however, sand color and fish population do not affect water levels.

If a tidal bulge moves across the open sea, it has plenty of space to stay relatively flat. If that same bulge hits a coastline and is "squeezed" against the land, then the water level is forced to rise higher, increasing the tidal range at the coast.

If a location passes through only one water bulge and one low point in 24 hours due to its geographic position, then it has a single daily cycle. If it has one cycle, it is a diurnal pattern.

If the Earth is spinning while water tries to move toward the Moon, then the water is deflected by the planet's rotation. If this deflection causes water to "pile up" in certain corners of the ocean, then it alters the local tidal range.

If tidal energy moves up a river, it rubs against the bottom and sides of the riverbed. If friction consumes that energy and the water volume spreads out, then the vertical difference in the tides, or the tidal range, will shrink.

If the Sun and Moon line up to pull on the water together, then the high tides are at their maximum and low tides are at their minimum. If the difference between high and low is maximized, then these events produce the largest tidal range.

If a location experiences two tidal cycles a day (semidiurnal) but the geographic shape of the coast causes one high tide to be much taller than the other, then the pattern is "mixed."

If a body of water is mostly surrounded by land with only a tiny opening (like the Strait of Gibraltar), then only a small amount of the ocean's tidal bulge can enter. If very little water enters, then the Mediterranean has a very low tidal range.

If the distance between high and low water is 20 feet, a large strip of beach will be affected. If that distance defines which land is wet or dry, then the intertidal zone is created by the tidal range.

If a harbor is shallow and the tide drops by 10 feet, then a ship that was floating safely might run aground. If the captain knows the tidal range, then they can time their arrival for high tide to ensure there is enough water.

If low air pressure allows the ocean to rise and wind pushes water onto the shore, then the water level will be higher than a normal high tide. If the water is higher, then the observed tidal range for that day increases.

If the Moon and Sun are usually aligned more closely with the Earth's center (equator), then the gravitational "pull" is strongest in those regions. If the pull is strongest there, then the water bulges are larger, creating a higher tidal range.

If the time it takes for a wave to bounce from one end of a bay to the other is the same as the 12.5-hour tide cycle, then the water starts to swing back and forth rhythmically. If this "swinging" adds to the tide's height, then it is called resonance.

If the force of moving water erodes rocks and moves sand, then a larger difference in water levels creates more erosion. If geologists analyze this force, they are studying the impact of the tidal range.

If scientists need a consistent baseline to measure from, then they average the lowest tides over many years. If this average is set as "zero," then any tide below that is a "minus tide" and helps define the tidal range.

If the range was only about gravity, it would be the same everywhere; however, because it changes based on land location, bay shapes, and ocean depths, it is a geographic study. Answer D is incorrect because the tidal range is not universal.