Brazil Erosion by nature is generated by wind, waves, littoral currents, near shore currents, and geological influences. Erosion cycle will vary a lot due to the the local beach conditions. Research projects have shown that the size of sediment and type of sediment also effect the erosion cycle. Small sediment are easier to transport by waves and currents Larger sizes of sediment do more harm when transported. Also the "pump-effect" from wave weight makes it easier for small sediment to be transported. The pump effect causes raize and fall of the pore pressure and release, lift the sediment up in water. Great Lakes

 

It is to be considered that all elements, Meteorological , Geotechnical, Marine and even Space effects(moon+ sun gravity)meet on a shore and also that these elements are mobile and can develope strong forces each - and worse together. 1 )Erosion by nature is a physical process where the different material particles in movement will effect each other and causes erosion. There are many parameters on a beach to be considered when to measure an erosion cycle.Generally, the nature behavior could be comapairesed to a Domino bricks game.If the temperature raize or fall it will start a circulation in the air and generate winds.

The winds then will generate waves. The waves will generate currents near shore which will transport the sediment(sand) away. Wave's weight hit the bottom surface and raize pore water pressure(a form of "strike back") which press the sediment up into the water and make it easier for to be transported away.

2) There are however some general parameters in nature behavior.The littoral (coast parallell) currents generally have one main direction with sediment transport. Near shore the currents also change directions with the tide. In a tide cycle from ebb to flood the direction of the currents will change nearly/or 180 degree and vice versa when changing from flood to ebb. Also for examples, grounds and stones on a local place will effect the current directions.Second picture is a small excerpt from an X-Term Grid in marine measures(Indicators are usually set to range 4min, 24 hours and synchronized but would be to large to show here).Even if the wave directions are similar there are lots of activities below water surface all the time.

3) It is a common idea that there is no ground water on shores and near shores and also that heavy rain will not effect the erosion on a beach. A common attitude is that "there is so much water outside so it is nothing to care about". But a land slide can occur on a place near the sea due to heavy rain as well as it can occur inside a country. The ground water is there and also the the pore water pressure.The pore pressure and ground water will raize or fall with air pressure changes and also if land is loaded by houses,buildings etc. This is to mean that when a wave hit the shore, it will cause a load and the load will increase the pore water pressure.When a wave retires there will be an over preussure on the beach which put the sedimennt up into the water and make it easier for currents to transport it away..This will continue for every wave and that is why it is called the pump effect.

The first section will effect a local place but there is nothing we can do about that. The other sections are easier as we here are able to measure and capable to put in some actions in order to keep the sediment on place and avoid erosion.

Besides the above mentioned parameters there are also effects from winds on a beach (wind erosion). In some areas there are earthquakes which causes high waves and tsumani waves.Temperature changes in water near shore can cause ribs, high speed currents perpendicular out from a beach and can be very dangerous for swimming people. Also techtonic movements can effect the erosion

Waves and winds is a large subject itself so we are not going to deep in this here, as there are many books and reports that can be be studied. The below is just a very small peace.

When wind start there will be small waves(capillarity waves) which structure is dependent of the water tension.When the wave length has grown there will be small groups of waves which structure is determined by gravity (graviation waves).The waves are groving fast but only in the wind direction. When the wave height increase more than 1/7 of the wave length the top will be unstable and break into white foam. When wave movement reach the bottom surface the wave base will slow down in speed due to friction, then the wave top passes by and the wave breaks.

Waves can be very powerful especially during high speed wind conditions for example in hurricane areas so buildings have to very strong. Hurricane waves can hit a beach with a pressure of more than 70 tons/square meter.A tsunami wave from earthquake hit Lissabon 1775 and destroyed a third of the town and killed about 50.000 people.

Glossary:

Athmosphere: The air mass which surround the earth.

Low = low pressure air. Air circulation rotate in a left hand circle on the northen hemisphere and right on the southern

High = high pressure air. Air circulation in right hand circle on the northen hemisphere and left on the southern.

The same conditions occurs in water. Check for example your dishtray when you empty water. Water will always get out in a left hand circle on the northern hemisphere and right hand circle on the southern hemisphere.

Sediment = The soil material on a beach and in water. Sand, mud etc.

Littoral currents = Coast parallell currents (usually one main direction) outside a shore

Near shore currents = Currents that change directions with tide and also dependent of bottom surface, such as stones, grounds, constructions etc.

Ribs = Temporary currents near shore usually perpendicular to the beach. Can be very strong

Waves can be descibed by :Height - Speed - Amplitude(period from one top to next to)

Summer waves = Waves during summer conditions. Winter waves = Waves during winter conditions

Tsunami wave = Wave caused by for instance earthquake. Will be very high and can destroy land. A tsunami is formed by movments in the the bottom layer and effect a column of water.
A warning center PTWC, Pacific Tsunami Warning Center was made 1948 located in Honululu.area

1. Movements in bottom layer effects water. 2. A serie of waves moves out with a height of less than one meter in open sea. 3. When a wave approach to land will the energy be concentrated to a smaller volume/ area and causes the wave to grow in height. ( Speed in open deep sea can be 800km/h. like a Boeing 747. Height will vary over 100m.)

 

Tide = Ebb and Flood. A period cycle of water level changeCertain printed schedules can usually be obtained from harbor charts. Also usually calculated years ahead for local places. Normal cycle around 6 hours.(This phenomenon is also used to produce electrical power. First hydro electric power station was built in Bretagne. 13.5m as maximum tide diff medium 8,5m diff..)	Tide is dependent of the moon graviaty and vary a lot on different local places on earth. Tide can vary 18 m (~59 feet).
Ebb= regular low water condition Nip flood=happens when the moon is half and forces are smaller than usual.	Flood = regular high water condition. Spring Flood =happens when moon is full or down and on the same line to the sun.Forces are added and flood is half a time bigger than usual

 

High water= Water level usually dependent of air pressure. Higher than normal for a local place.

Low water= Water level usually dependent of the air pressure.Lower than normal for a loca place.

No scheduled change Usually every harbor has there own real time indicators.

Air pressure in standard athmospere = 1013,5 millibars or Pascal

Ground water = The water in soil layers. Will vary in height with heavy rain and air pressure as well as if it is loaded by constructions.(nature law)

Pore water pressure = The hydraulic pressure in soil layers. Is effected by air pressure and loads.

Pump Effect = The raize and fall of the pore water pressure when waves load and unload weight at the bottom surface.

Techtonic Movements = The movement of mountains, landmasses and continents.(For an example- South America has moved from Africa a long time ago) Mountains and landmasses are still moving around. Tables might be obtained from geolocical institutes.

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