Tidal amplitude, often defined as half the difference between high tide and low tide, can be measured using various methods, including the amplitude ratio method which involves comparing water levels between stations.
The Amplitude Ratio Method
One technique for determining tidal amplitude relies on comparing water level data collected simultaneously at different locations: a control station (where tidal data is well-established) and a subordinate station (the location where you want to determine the amplitude).
According to this method:
- It requires simultaneous water level observations of high water at the control and subordinate tide stations.
- You must record water levels at 6-minute intervals during a rising and falling tide on each side of the peak high water at both the control and subordinate station(s).
Steps Involved in This Method
To apply the amplitude ratio method, follow these steps:
- Select Stations: Identify a control tide station with reliable, long-term tidal data and the subordinate station where you need to determine the tidal amplitude.
- Plan Observations: Coordinate simultaneous water level observations at both stations.
- Execute Recordings:
- Begin recording water levels as the tide rises towards its peak (high water).
- Continue recording through the peak high water.
- Record as the tide falls away from its peak.
- Ensure recordings are taken at 6-minute intervals throughout this period.
- Collect these observations for at least one rising and falling tide on each side of the peak high water at both the control and subordinate stations.
- Analyze Data: Compare the observed high water levels (or the tidal range around high water) at the subordinate station to those simultaneously observed at the control station.
- Calculate Amplitude: Using the known amplitude or tidal range at the control station and the observed ratio or difference during the simultaneous observation period, you can calculate the amplitude at the subordinate station. This often involves establishing a ratio between the tidal ranges (or high water levels relative to a reference point) at the two stations.
This method is particularly useful for determining tidal characteristics in locations where long-term data is not available by relating them to nearby established stations.
