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. The vertical clearances of bridges along navigable waterways are given as heights in feet above mean water height because it provides a consistent reference point for determining whether a vessel can safely pass under the bridge. Mean water height refers to the average water level over a specific period, usually calculated based on tidal data. By specifying heights above mean water level, it ensures that the clearance accounts for any variations in water levels due to tides. This ensures that vessels have sufficient space to pass under the bridge without risking contact or damage.
To determine the clearance of a bridge above mean water level, you would typically need access to bridge specifications or engineering drawings, which provide information on the bridge structure and its vertical clearance. These documents would usually specify the height above mean water level at different points on the bridge, allowing mariners to assess whether their vessel can safely navigate through.
2. Knowledge of tides is crucial in military landing actions for several reasons:
a) Planning and timing: Tides can significantly affect the depth and accessibility of waterways, especially in coastal areas and estuaries. Military landing operations often require vessels to approach and navigate through unfamiliar territory, which may include shallow areas or potential obstacles. Understanding tidal patterns and their impact on water levels helps military planners determine the optimal timing for operations, ensuring that vessels can safely navigate through shallower regions.
b) Beach and shoreline conditions: Tides also play a role in determining beach conditions, such as the width and slope of the shoreline. Landing operations heavily rely on assessing whether a beach can support the safe and efficient disembarkation of troops and equipment. Knowledge of tides aids in identifying suitable landing sites by understanding how tidal variations impact the beach's suitability, including the presence of obstacles, currents, or even submerged hazards.
c) Amphibious operations: Amphibious assaults often involve a combination of land, air, and sea operations. Tidal information is crucial for coordinating the movement of amphibious assault vehicles, landing craft, and other vessels involved. Knowing the timing and height of tides allows military planners to synchronize actions, ensuring that the necessary vessels and equipment can operate effectively.
To obtain tidal information, military forces typically rely on specialized hydrographic charts, tide tables, and forecasts. These resources provide details about tidal patterns, water depths, and related information necessary for planning military landing actions.