Measuring the Outgoing Tide of Bolinas Lagoon

Overview

Objectives/Goals The purpose of my project was to determine how fast Bolinas Lagoon drains in the period between high tide and low tide, to see if there is a lag between the calculated low tide and the actual low tide, and to find out if the water is warmed as it sits in the shallow lagoon. Methods/Materials Procedure: Take three preliminary temperature readings at different points along the lagoon. Measure distance of 100 feet along the side of the narrow channel where water exits the lagoon. Mark distance with cones. Every fifteen minutes, throw a grapefruit into the water. Time how long it takes for the grapefruit to travel the 100 feet between the cones. Measure the temperature of the outgoing water every hour. Over the course of 7.5 hours, I threw a total of 35 grapefruits into the channel and measured their speeds. Materials: 2 cones for marking the 100 foot distance thermometer 35 grapefruits stopwatch tide tables for Bolinas, California data table to record current speeds and water temperatures Results The water flowed increasingly faster until mid tide, and then it slowed down. There is a lag of about 45 minutes between official calculated low tide and actual low tide because the bottom of Bolinas Lagoon drags on the water as it drains. There is a lag of about 30 minutes for high tide. The water was not warmed as it sat in the lagoon. Conclusions/Discussion The water probably drained the fastest out of the lagoon at mid tide because it had a chance to gain momentum and overcome the drag effect of the mud. However, at the beginning of the tide cycle, the water was still dragging on the mud, and this created the lag. The water may be warmed as it sits in the lagoon. However, the day of the experiment, it was overcast and rainy, so the sun never had a chance to heat the mud.

Competition history

• CSEF 2006 Earth Sciences/ Planetary Sciences/ Physical Environments · Entry J0607

Resources

• CSEF project summary ↗

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