While working with scientists and educators at the Cape Cod National Seashore, one of the scientists pointed out the discrepency between the tides at the beach and a nearby estuary. The tides at the beach bordering open ocean is roughly a twelve hour cycle, with 6 hours of high tide and 6 hours of low tide. The tides within the neighboring estuary, which is connected to the ocean by a narrow channel, are roughly 8 hours of high tide and 4 hours of low tide. As the water flow out of the estuary, there is less "push" by the water, so the draining of the estuary slows. But when the ocean waters begin to rise with the approaching high tide, the water rapidly flows back into the estuary.
This was such a fascinating phenomena, so we wanted to create concrete visual experiences to accompany the description. Because time lapse is relatively easy and inexpensive to do, consider developing your own movies for educational projects.
Tides at Beach 9.8 mb MPEG
Tides in Estuary 27.2 mb MPEG
The movies were made with a Kodak DC-290 digital camera with a 128 mb compact flash memory card. Camera was set to take a picture once a minute. Despite being secured to a metal railing, the strong winds buffeted the camera, creating the noticeable shake of frames.
Selected images from movies: Low tide at beach and low tide in estuary (second image).