VERTICAL DATUM, DEPTH AND HEIGHTS


1. What is the main cause of tides? 2.


During the approximate 28 day lunar orbit the interaction between the moon, sun and earth alters. This affects the magnitude of the tides causing spring, neap and intermediate tides. When during the lunar cycle do spring, neap and intermediate tides occur?


3. 4.


The difference between successive high and low waters is known as the range of tide. Which is greater, a spring range or a neap range?


The time at which successive high and low waters occur becomes later day by day. Why is this?


5. What are the three basic tidal patterns? Give a brief description of each. 6. Match the following tidal terms to the illustration below.


a) Chart Datum (CD) b) Charted depth (below CD) c) Clearance of bridge (above HAT) d) Depth of water e) Drying height f ) Height of light above (above MHWS) g) Height of tide h) Highest Astronomical Tide i) Mean High Water Neaps j) Mean High Water Springs k) Mean Low Water Neaps l) Mean Low Water Springs


m) Neap range n) Spring range


(HAT)


(MHWN) (MHWS) (MLWN) (MLWS)


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