These questions refer to tides.
1. Why are vertical clearances of bridges along navigable waterways given as heights in feet above mean(average) water height?
2. Why would knowledge of tides be of any importance in a military landing action?
1. Vertical clearances of bridges along navigable waterways are given as heights in feet above mean water height for several reasons:
- Consistency and Standardization: Using mean water height as a reference point ensures that measurements and clearances are consistent across different locations. Mean water height is calculated based on a long-term average, smoothing out the effects of tidal fluctuations and providing a reliable reference point.
- Safety and Navigation: Navigable waterways accommodate boats, ships, and other vessels. By specifying clearances above mean water height, bridge designers and planners ensure that vessels can safely pass under bridges without any obstructions. This information is crucial for navigational safety and preventing accidents.
- Predictability: Tidal fluctuations vary throughout the day, and using an average height provides a predictable reference point for bridge measurements. It allows bridge clearance calculations to account for the maximum height of the tidal cycle and helps ensure that vessels will always have sufficient clearance under the bridge, regardless of the tide.
To obtain the mean water height and calculate the clearance, tidal data is collected over an extended period at tide gauges located nearby the bridge. These gauges measure the water level relative to a fixed benchmark and record the changes in tidal height over time. By analyzing this data, the average tidal height can be determined, and bridge clearances can be established.
2. Knowledge of tides is essential in military landing actions due to the following reasons:
- Navigation and Timing: Tides significantly affect water depth, currents, and the distance to the shoreline. Understanding the tide patterns allows military planners to determine the best time to launch a landing operation. At high tide, there may be more water depth for boats to approach the target area, whereas at low tide, the water may recede, revealing potential obstacles or creating challenges for larger vessels. By considering the tides, military forces can optimize their approach and timing to maximize their operational effectiveness.
- Beach Conditions: Tides influence the condition of the beach during a landing operation. The height of the tide affects the width of the beach available for landing, as well as the slope of the shore. High tides may provide a broader landing area, while low tides may expose hazards such as rocks or reefs. Knowledge of tide cycles allows military forces to plan their landing based on the most favorable beach conditions, reducing the risks associated with landing on uneven or hazardous terrain.
- Concealment and Surprise: Tidal fluctuations can impact the visibility of approaching forces. During high tides, the water may cover potential landing craft or provide greater concealment for amphibious operations. Understanding the tides can help military planners take advantage of these natural factors to enhance the element of surprise and maintain strategic advantages during a landing action.
To obtain knowledge of tides for military purposes, extensive research and analysis of tidal patterns specific to the target area are conducted. This may involve consultation with experts in oceanography or the use of specialized tide prediction models and charts. By utilizing this information, military commanders can better plan and execute landing actions with increased efficiency and effectiveness.