GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S GEOMETRIC DESIGN OF TRANSPORTATION INFRASTRUCTURES 315 – GDT 711S NATURAL PHENOMENA AT THE SEA AND OCEAN BN NAKAMELA 1 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S SEA NATURAL PHENOMENA • Natural phenomena are events that happen as a results of the forces of nature • Natural phenomena that occur in the sea, tend to have effects on the coastal areas and hence, they affect the planning, design and operations of the port • These phenomena cause sea disturbances and the important once to the harbour/port engineer are; – The Winds – The Tides – The Tsunamis • These disturbances are a result of the dynamic interaction of the earth spheres • All of these cause waves on the surface of the water body Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 2 2 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S BRIEF PHYSICAL GEOGRAPHY OF THE EARTH • The earth (or the globe) consists of three zones or spheres • These zones are in a state of dynamic equilibrium; 1. Lithosphere • The land part of the earth or the solid outer part of the earth 2. Hydrosphere • The part of the earth covered by the body of liquid water 3. Atmosphere • The envelope of gases, which covers both, the lithosphere and the hydrosphere Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 3 3 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S LITHOSPHERE G. ATMOSPHERE Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 4 4 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S WIND • This is a meteorological phenomenon, which occurs within the troposphere zone (lowest zone of the atmosphere) • It causes the movement of air in a specific direction and blowing in a horizontal direction, parallel to the surface of the earth • In harbour and port engineering, the effects of wind blowing is important in two aspects; The force it exerts when it blows against an object in its path The disturbance it creates when it blows over the surface of the ocean • This disturbance is normally proportional to its speed and appears in the form of waves • The formation of sea waves takes place in the open sea as a result of the action of the wind Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 5 5 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S WIND • Sea waves are of two types; –Oscillatory waves These are stationary waves (cause stationary water particles) –Translational waves These possess forward movement (cause water particles to move in the direction of the waves) They start as oscillatory waves and change as they approach the shoreline They are the main concern of the port and harbour engineer Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 6 6 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S THE THREE TYPES OF HARBOURS Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 7 7 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S ANATAMY OF A WAVE Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 8 8 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S TIDES • This is the rise and fall of sea levels, which also result in currents • Tidal heights and currents have a significant effect on navigation • They are a coastal phenomenon (as they are easier to observe where the land and water meet, but they exist everywhere) • Tides are caused by combined effects of three processes; – Gravitational pull of the moon – Gravitational attraction of the sun – Centrifugal force of the rotating earth • The earth and the moon spin as pair around a common point (called a Barycentre) – The earth orbits the sun once every year – The moon orbits the earth approximately every 29 1/2 days (the Lunar month) Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 9 9 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S ANATAMY OF A WAVE MOON EARTH Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 10 10 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S ANATAMY OF A WAVE MOON EARTH Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 11 11 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S SPRING TIDES AND NEAP TIDES • Tidal ranges vary by day, by month as well as by year • There are two periods during the month when the positions of the three bodies (the earth, the moon and the sun) are of interest • At a time when their positions form a straight line –This occurs during the new moon and the full moon –During this time the gravitational effects of the sun and the moon become additive –The resulting tides rise higher and fall lower than at other times –These tides are called SPRING TIDES Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 12 12 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S EARTH – MOON – SUN POSITIONS FOR SPRING TIDES Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 13 13 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S EARTH – MOON – SUN POSITIONS FOR SPRING TIDES • At a time when their positions form a right angle (90o) – This occurs when the moon is in the first and third quarters – This is half way between the new moon and the full moon – The sun and the moon pull at right (90o) angle to each other – Their effects are partially cancelled out by one another – The resulting tides rise and fall less than at other times – These are called NEAP TIDES which have smaller tidal ranges Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 14 14 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S EARTH – MOON – SUN POSITIONS FOR NEAP TIDES Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 15 15 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S EFFECTS OF TIDAL CHANGES ‐ HARBOUR FALLING DRY DURING LOW TIDE ITEMS PACKED ON A PALLET HARBOUR OF GOREY, JERSEY Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 16 16 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S TIDAL PATTERNS OR CHARACTERISTICS • Tides can occur within a day in three ways –Diurnal Tides These occur as a single high and a single low tide each day (i.e. one tidal cycle per day) They tend to occur in certain areas when the moon is at its furthest from the equator –Semi‐diurnal Tides Two high and two low waters occur daily of relatively similar ranges They are more likely to occur when the moon is over the equator –Mixed Tides Also occur as two high and two low tides per day But the successive high tide and low tide levels that vary significantly from each other They tend to occur as the moon moves furthest north or south of the equator Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 17 17 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S TIDAL PATTERNS OR CHARACTERISTICS Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 18 18 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S TIDAL PATTERNS OR CHARACTERISTICS Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 19 19 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S TIDES Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 20 20 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S DIURNAL TIDES • A diurnal tidal cycle is characterized by a single high tide every 24 hours and 50 minutes Diurnal tides typically occur in partially enclosed basins, such as the Gulf of Mexico Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 21 21 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S BEHAVIOUR OF DIURNAL TIDES • A diurnal tidal cycle is characterized by a single high tide every 24 hours and 50 minutes Diurnal tides typically occur in partially enclosed basins, such as the Gulf of Mexico Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 22 22 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S SEMI DIURNAL TIDES • A semidiurnal tidal cycle is characterized by two high tides daily of about equal heights occurring about 12 hours and 25 minutes apart • The east coast of the United States usually experiences semidiurnal tides Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 23 23 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S BEHAVIOUR OF SEMI DIURNAL TIDES • A semidiurnal tidal cycle is characterized by two high tides daily of about equal heights occurring about 12 hours and 25 minutes apart • The east coast of the United States usually experiences semidiurnal tides Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 24 24 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S MIXED TIDES • In a mixed tidal cycle, the tides also occur twice daily, but the two high tides and two low tides are unequal in height • Mixed tides occur on the west coast of the continental United States and in Alaska and Hawai‘i Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 25 25 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S BEHAVIOUR OF MIXED TIDES • In a mixed tidal cycle, the tides also occur twice daily, but the two high tides and two low tides are unequal in height • Mixed tides occur on the west coast of the continental United States and in Alaska and Hawai‘i Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 26 26 GEOMETRIC DESIGN OF TRANSPORT INFRASTUCTURE 315 – GTD711S Geometric Design of Transportation Infrastructures 315 – GDT 711S BN NAKAMELA 27 27
