Work's of river, winds, seas and their Engineering Importance

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1. WORKS OF RIVERS, WIND AND SEA AND THEIR ENGINEERING IMPORTANCE L e ss o n 7 Baculo, Ashley, B a li w a g , A u b r e y B i n o n d o , Binondo, Zara Veronica C. Canono, Ryan

2. R I V E R S As the rivers have a beginning which is called head. The place where as river ends in the sea or lake is called mouth. In all the cases, the slope of the rivers at the head is high so that it can carry all the materials (the coarse and fine weathered products) from the parent rocks down. The slope slowly decreases and in the plains it is smaller. Thus the shape of the slope from the head to the mouth is concave (facing the sky)

3. P L A Y F AIR’S L A W ( F U N C TI O N O F A R I VER) John Playfair

4. WHO IS JOHN PLAYFAIR? S c o t t i s h G e o l o g i s t a n d m a t h e m a t i c i a n M a r c h 20 , 1 7 4 8 , B e n v i e , F o r f a r s h i r e , Scot. D i e d J u l y 2 1 8 1 9 , B u r n t i s l a n d , F i f e E x p l a n a t i o n a n d e x p a n s i o n o f i d e a s o n uniformitarianism. He was the first to propose that a river c u t s i t s o w n v a ll e y a n d w a s a l s o t h e f i r s t to recognize the transport role of glaciers.

5. P L A Y F A I R ’ S L A W ( F U N C T I O N O F A RIVER) This law indicates how deep valleys and landforms have been formed. These landforms have been formed by the three geologic functions of the rivers:

6. GEOLOGIC FUNCTIONS OF THE RIVERS EROSION T R A N S P O R T A T I O N DEPOSITION

7. EROSION The erosion is one of the most expressive features of river which is turbulent with currents in all directions. Most rivers carve the river valley by erosion. T h e r i v er ero d es i n f o u r m a i n w a y s : Attrition Corrosion Corrasion H y d r a u l i c a c t i on

8. H Y D R A U L I I C A C T I O N The waves crash against rock and compress the air in the cracks. This is the force of the water of the fast flowing rivers that can dislodge materials from the river banks and river beds.

9. C O R R A S I O N ( A B R A S I O N ) Eroded particles in the water scrape and against the rock (cliff), removing small pieces. This is the abrasive force producing a mechanical erosion of rocks by the sediments the river carries.

10. A B R A S I O N : T H R E E F A C T O R S If the transported materials is hard in relation to the bed, the bed gets affected and we a r s d ow n . If both are hard then the bed gets polished I f t h e b ed i s h a r d er t h e b ed i s n ot a f f e c t e d .

11. A T T R I T I O N Eroded particles in the water ash into each other and break into smaller pieces. Their edges gets rounded off as they bash into each other. This is due to the rubbing of the particles being carried by the river when they are thrown at each other.

12. C O R R O S I O N ( S O L U T I O N) In this process the water dissolves particles of the river banks or bottom and carries them in solution. Weak carbonic acid in sweater dissolves rock like chalk and limestone.

13. T R A NSP O R T A T I O N O F ERODED MATERIALS

14. T R A N S P O R T A T I O N O F E R O D E D MATERIALS The materials that have been eroded have to be transported down the river. There are ways in which the river can transport the materials dislodged by it. Dissolved Load Suspended load: the fine particles of Sand silt and clay can remain in suspension. Bed Load: The large-sized materials settle to the bed of the river and move along the bed by rolling, sliding or by sudden movement (saltation). This bottom load is also called the traction load.

15. D E P O S I T I O N ( A L L U V I A L D E P O S I T I O N) When the velocity of water in river is not enough to carry the load of soil particles it has been carrying, it deposits the load at the places of low velocity. This usually happens in the regions where the slope of the river bed becomes gentle. These Function act on the following three physical processes involved in the formation of river valleys, namely: Deepening of the river valley L e n g t h e n i n g or s h o r t e n i n g of t h e r i v e r v a ll e y W i d e n i n g t h e r i v e r v a ll e y s

16. C A RR I E D O R D E P O S I T E D P A R T I C L E S B Y RIVER WATER Different particles of soil require different velocities. F or t h e m t o b e s o u r c e d b y w a t e r For them to be carried in water T o b e d e p o s i t e d on t h e i r p a t h .

17. F i g u r e 1 . F i e l d s of erosion, transportation and deposition of r i v e r s e d i m e n t s i n t h e f l o w o f rivers.

18. STREAM CYCLE

19. Juvenile or Youth Stage (Upper Course) This is the stage of high downward vertical erosion. It develops the following c h a r a c t er i s t i c f orm a t i o n s : V- shaped valleys Gorges and canyons Rapids and cataracts (Rapids of greater dimensions are known as cataracts) Waterfalls Holes Piracy (Capturing of a streamlet that flowed into one river another stream that flows into another river)

20. EXAMPLE:

21. Maturity Stage (Middle Course) This is the middle course of a river where the gradient is gentler and the river valley becomes wide, leading to the following features: Meanders Flood plain

22. M e a nd e r s The term meander is derived from river Meanderz in Turkey, which flows in loops. In the wide plains the river may be made to bend and take a curve due to some obstructions. Then the velocity around the outside bend becomes very much higher and hence the river cuts down the river bank. As the velocity inside the bend being less, deposition of fine particles takes place which is shown. The clay deposits are found more on the inside of the river bends where the velocity is low. As erosion cuts away bank on one side and deposition takes place on the opposite side, the river migrates laterally and produces a meandering river

23. EX A M P L E:

24. Flood plain The flood plains occur in the middle course of the river that has formed its maturity. The valley characteristics are absent and the river flows along a wide and flatter region. Overflow of the banks and flooding happens during floods. This leaves behind deposits of silt on both sides. These are called flood plains

25. EXAMPLE:

26. The following are the geomorphologic features of this region: Levees- : The natural embankments formed by the river in the flood plains are called levees. As the floodwater in the river spills on the flood plains it loses energy and coarse materials are deposited at the edges. Over the years raised edges are formed which are called levee Oxbow lakes- The meandering river can cut across the flood plain and form the oxbow l a k e s . T h e o x b ow l a k e s c a n d e v e l op i n t o s w a m p s i n c o u r s e of t i m e . Braiding- When the river reaches the end of the middle course the river deposits more and more of the load it has been carrying and may break up into a network of interconnected channels resembling the strand of a braid. This happens more often towards the beginning of the old stage of the river.

27. E X A M P L E:

28. OLD AGE (Lower Course) In the last stages of the river just before it joins the sea or lake, the flow becomes gentle as the slope of the river in considerably reduced. If it joins the sea, there are waves, sea currents and also change in the salinity of water. The suspended material is deposited. If the amount of material is not large then it will be carried away by the sea by its currents and waves. This is what happens to the small rivers on the west coast of peninsular India. However if the rivers are large like those which flow into the Bay of Bengal and the amount of suspended materials carried by river is very large, a large amount of the suspended materials will be deposited at the mouth of the river to form deltas.

29. - Delta-Building: The subject of delta-building is very interesting and can be explained as follows. The deposition of material at the mouth of the river and into the sea materially increases the length of the river. This decreases the slope and hence more deposition happens. For example, if the slope was 2 ft in 90 miles and if the length of deposition of sediments of the river is increased to 100 miles, the slope reduces from 1 in 45 to 1 in 50. The velocity of water decreases and more deposition takes place. Also during the floods because of the raising of the beds, the river will have to branch off before it falls into the sea to increase the flow and thus form the typical delta.There are many types of deltas of which three are the typical.

30. E X A M P L E

31. 1) Arcuate deltas : I t l oo k s l i k e t h o s e of t h e r i v er G a n g es a n d N i l e.

32. E X A M P L E :

33. 2) Birds foot deltas It appears like that of the Mississippi river. These rivers carry extremely fine particles and clays. The deposits do not allow much flow under the surface (the deposits being clayey or impervious), so that the flow of water is concentrated in a few large channels which form a pattern of the bird’s foot. Thus this type of deltas has clay deposits.

34. EXAMPLE:

35. 3) Estuarine filling: As in the Hudson River which flows into an estuary and where the deposits are built in the form of long bars at the mouth of the river. The forms extensive filling of soil bars or marshes.

36. The rivers that fall into lakes will also build deltas. The deltas, built in lakes and in land seas or bays, are more perfect than those built in the open ocean with strong currents and waves. The deltas built in the seas will be usually irregular. The three stages or courses do not depend on the age of the river but on the present performance of the river at a given place which depends on many present factors. It is also interesting to consider the two basic physiographic concepts in river flow that of (a) base level and (b) profile of equilibrium which varies with the flow.

37. a) Base Level : This is the level that controls the depth of the stream erosion. No stream base level c a n b e b e l ow t h e s ea l e v e l . . A base level is the depth limit of the valley and is controlled by the water level in the body of water into which it flows down (ocean, sea, lakes, etc.).

38. b) Profile of equilibrium : A stream is said to have reached its grade or profile of equilibrium when its slope and volume of water it carries are in equilibrium with the sediment load it transports. The annual and seasonal fluctuations in volume and velocity bring about continual readjustments of their profile. The gradient is expressed as slope of the profile of equilibrium at the steady state of flow of the river with no erosion or deposition. It is expressed in meters per kilometer, meter or feet per mile.

39. No implication of years is to be read into the terms juvenile, youth and old stages. It only represents the various stages of development of the river. Thus a youthful stream in hard rock, high above the base level (profile of equilibrium) may be millions of year of age, whereas the old stream near the base level may be only a few thousand years of age.

40. REJUVENATION OF RIVERS As already indicated, youth and old age does not denote the age of the river but only whether it is eroding (juvenile) or is in equilibrium or in depositing (old age) at present. Thus if a mature river has its gradient increased for example, by lowering the sea level or some construction then the river will work to reduce the gradient by cutting down the previously deposited flood plain until the former gradient is again e s t a b l i s h e d . T h i s i s i n a cc or d a n c e w i t h t h e P l a y f a i r ’ s l a w .

41. CORIOLIS EFFECT AND FERREL’S LAW T h e e f f e c t w h i c h c a u s es t h e d e f l e c t i on of a b o d y i n mo t i on on e a r t h d u e t o t h e rotation of the earth is called the Coriolis Effect. According to Ferrel’s law, due to this effect if a body moves in any direction on the earth’s surface, the deflection force will act to the right in the northern hemisphere and the left in the southern hemisphere. According to this law a river flowing in the north direction in northern hemisphere tends to erode the east banks more than the west banks. Similarly a river in the northern hemisphere flowing in south direction tends to deflect to the west; land ero s i on w i l l t a k e p l a c e mo r e of t h e w e s t b a n k s t h a n t h e e a s t b a n k s . H owe v er i n a l l the cases the resistance of the material to erosion and slope of the land will also play a prominent part.

42. W I ND The movement of air over the surface of the earth is called wind. Wind performs all the three functions of erosion, transportation and deposition of the weathered products. The wind deposits are also called Aeolian deposits.

43. EROSION WORK OF WINDS T h e p r o c e s s es of ero s i on d u e t o w i n d a r e ( 1 ) D e f l a t i o n , a n d ( 2 ) A b r a s i on

44. 1. Deflation The act of removing the loose particles of the earth from one area and forming depression as shown in the figure is called deflation. By this process of removing the s a n d t o t h e g r o u n d w a t er l e v e l , o a s i s i s f o r med i n d e s e r t s .

45. Abrasion Abrasion is the process of impact of the coarse particles in the wind against formations like understanding rock and eroding them. Most of the coarse materials in the wind remain in the lower 30 to 60 cm height of the wind from the ground as bed load and some coarse sand particles will be swept by rolling them on the ground. Hence the rock erosion produces profiles of upstanding rocks as shown in figure. In such cases there will be more erosion at the lower level and very much l e s s ero s i on a t t h e h i g h er l e v el of t h e u p s t a n d i n g r o c k s .

46. SAND STORMS AND DUST STORMS While the lower part of the wind consists of sand, the upper part is mainly the fine particles of dust. Thus the lower part produces the sand storms and the upper part produces dust storms. SAND STORMS describe an exceptionally strong wind, which picks up and carries a large amount of sand in the atmosphere. They can reach up to weight of 10-50 ft. DUST STORMS carry much smaller particles, which can be carried higher and further tyan sand storms.

47. D E P O S I T I O N O F S E D I M E N T S The velocity of the wind carrying the particles may get reduced by some obstructions like hills, mountains, forests sudden change of climate presense of water bodies like rivers, sea, fall of rains, etc. This reduction of velocity forces deposition of the particles the wind is carrying, and they form typical Aeolian deposits. TWO (2) IMPORTANTS TYPES OF DEPOSITS: Sand Dunes Loess

48. S A N D A N D D U N E S The sand dunes are formed by deposition of sand carried by winds. It is heap of sand conical in cross section with a gentle slope on the windward side and a steeper slope on the leeward side. There is much type of formations such as the (1) LONGITUDINAL DUNES, (2) TRANSVERSE DUNES and the most common (3) CRESCENT SHAPE DUNE called BARCHANS. The dunes may get stabilized as “ fixed dunes “ in one place or like the barchans mo v e on t h e d i re c t i o n s of t h e w i n d s . S a n d d u n e s c a n b e f orm e d a t t h ree ( 3 ) k i n d s of l o c a t i o n s n a m e l y : N e a r s e a s h ores a s s h ore d u n e s Bed of rivers as riverbed dunes I n l a n d a s d e s e r t d u n e s

49. P L A N V I E W O F S A N D D U N E S Crescent Shaped Dune called Barchans T r a n s v e r s e D u n e L o n g i t u d i n a l D u n e SEIFS are also called LONGITUDINAL DUNES. T h e y a re f ormed p a r a ll e l t o t h e d i re c t i o n s of t h e wind as shown in the figure. These are usually f o u n d i n t h e p l a c e s w h e re s t e a d y w i n d p re v a i l s . T h e s e d u n e s m a y e x i s t i n g re a t h e i g h t s a n d u p t o 20 m a l o n g l o n g d i s t a n c e s .

50. L O E S S D E P O S I T S The term loess was first applied to the loose unconsolidated deposits found along the Rhine River extending to the Black Sea. Loess is fine particles usually derived from flood plains and glacial outwash laid by the wind. It consist of the loosely arranged angular grains of calcareous silt, rich in quartz with calcium carbonate. It is the uniform size and composition formed without stratification. The loess deposits pose two (2) engineering problems: The collapese of its structure on wetting or saturation. Because of its losse structure, they are subject to frost heaving in cold countries, w h e n t h e y o c c u r on h i g h w a y l a y o u t s .

51. SEA- Seas and Oceans covered 70% of the Earth’s surface. The term “ sea “ is generally used for saline water bodies surrounded by landforms and also water bodies of shallower depth less than 4km. F O R M A T I ON O F T H E S H O R E L I N E sea waves, sea currents, the theory of formation of coastlines by erosion, deposition and sea level changes. Coral deposits SEA WAVES -The waves are created by the winds. This disturbance travels to the coast and gets its energy destroyed. The distance between the crests of adjacent waves is the wavelength in the deep part of the sea; waves are only oscillatory (goes only up and down). These are called oscillatory waves.

52. LITTORAL CURRENTS - The word littoral means pertaining to the shoreline. The movement of water up to the coast when the waves break is called swash and the return of the water back into the sea is called backwash. While the flow (velocity) of the swash is directed to the shore the currents set up by the backwash (which is called the rip current) usually act below the sea level and are directed to the deeper waters. W A V E S A N D C U R R E N TS Or d i n a r y W a v es T r a n s i t o r y W a v es Littoral Currents Rip Currents

53. FORMATION OF COASTLINE BY MARINE EROSION OF C O A S T A L R O C K S Four distinct processes. Abrasion: Waves hurl pebbles, sand boulders and other substances against base of cliffs, under-cutting the base of cliffs on the sea coast. Hydraulic action: The cracks in the cliffs are filled with sea water from the waves and its sudden release during the retreat of the waves cause the material around the cracks to break up. Attrition due to rubbing together of particles in the waves and get broken up. Solution (Corrosion): By chemical action leading to solution of some of the constituents

54. L A N D F O R M F O R M ED B Y M A R I N E E R O S I ON O F R O C K S O N S E A C O A S T S Landforms are created by the above erosion of the rocks beside the sea. Sea Cliffs

55. Landforms are created by the above erosion of the rocks beside the sea. Sea caves, Arches, stacks and stumps L A N D F O R M F O R M ED B Y M A R I N E E R O S I ON O F R O C K S O N S E A C O A S T S

56. Wave-cut platforms L A N D F O R M F O R M ED B Y M A R I N E E R O S I ON O F R O C K S O N S E A C O A S T S

57. FORMATION OF LANDFORMS BY COASTAL DEPOSITION the sediments entering the sea are carried away by the sea waves and deposited in the sea or alternately it may be taken to the other parts of the seacoast. deposits on the coast forms the landforms called 1.) beaches, 2.) spits and 3.) bars. Beaches: These are formed by the deposition of sand and gravel along the coast. In theory, beach is the zone extending from low water sea level to the upper limit of high water. Spits: Spit is a long and narrow extension of the beach into the sea. They are sand deposits formed by shore drifts.

58. FORMATION OF LANDFORMS BY COASTAL DEPOSITION 3. Bars: Bars are long deposits of sand formed in the sea parallel to the shoreline. This may be above or below the sea level. Those above the sea level are called barrier beach. Tombolo: If the bar forms a link to the mainland the link is known as a tombolo Lagoo n : A b ar s p i t c an e n c lo s e a portion of the sea

59. F O R M A T I O N O F L A N F O R M S B Y S E A L E V E L C H A N G ES A rise in sea level can form a fjord. Fjord is a narrow long valley. There are called shore lines of submergence.When the sea level falls and more of the land gets exposed they are known as raised beaches. The landforms formed by this process are called land or shores of emergence.

60. Types of Shorelines: Shoreline of submergence - A shoreline, characterized by bays, promontories, and other minor features, formed by the dominant relative submergence of a landmass. Also known as positive shoreline; submerged shoreline. Shorelin e of e m erg e nce - A s tra i gh t or gentl y c u r vin g s horelin e f or m ed by the dominant relative emergence of the floor of an ocean or a lake. Also known as emerged shoreline; negative shoreline. F O R M A T I O N O F L A N F O R M S B Y S E A L E V E L C H A N G ES

61. TYPES OF CURRENTS THAT AFFECT THE COASTLINE Underflow or rip currents and littoral currents – We noted that the waves that come to the shore with a certain velocity, after flowing up the slope of the beaches, the water returns to the sea with a velocity depending on the slope of the beach along the bottom. This current is called undertoe or rip current . Already dealt with in the current that moves along the coast is called littoral current . This current will flow parallel to the coast until depressions are found which will give an opportunity for seaward exit.

62. Tidal Currents – The rise and fall of the tide in an open coast does not produce much effect on the deposits on the shoreline. However if the tides are very high and the fall of the tide has to take place through a narrow exit then the large velocity at the place of exit may have some effect on the nearby deposits at that place. The high velocity can lead to erosion. TYPES OF CURRENTS THAT AFFECT THE COASTLINE

63. S E A W A LLS A N D BULKHEADS

64. S E A W A LLS A N D B U LKH E A D S Seawalls and bulkheads are the massive structures built alone the coast. (Built parallel to the coast.) Their faces may be vertical, sloping or parabolic to produce as little force on the wall as possible.

65. S E A W A LLS A N D B U LKH E A D S Bulkheads are made of steel or concrete or timber piles and they are used where the impact of waves is not very large. The large hollow prestressed concrete pipes have been used for shore protection near Chennai harbor with some success.

66. C O N S T R U C T I O N O F R E V E T M E N T S Revetments against the coast are usually built with large stone or concrete block big enough to resist the force of the waves placed on each other. It should also be built high enough to prevent overtopping of the ordinary waves. For economy, the height may be such that s t o r m w a v e s m a y j u s t s p i l l o v e r i t .

67. ROCK REVETMENTS In stream restoration, river engineering, and coastal engineering, “revetments” are sloping structures placed on banks or cliff in such a way as to absorb the energy of incoming water. Slope angle of layered boulders to absorb, rather than reflect

68. PREVENTION OF SILTING Corals are very small sea organisms that live in very large colonics especially near the tropics. They secret calcium carbonates and build coral reef. These coral deposits may be built on sand deposits in the sea. T h r ee t y p es of c o r a l s r e e fs d e p o s i t e d : Fringing reefs Barrier reefs Attols

69. FRINGING REEFS Fringing reefs grow near the coastline around islands and continents. They are separated from the shore by narrow, shallow lagoons. Fringing reefs are the most common type of reef that we see.

70. B A RR I E R R EE FS Barrier reefs also parallel the coastline but are separated by deeper, wider lagoons. At their shallowest point, they can reach the water’s surface forming a “barrier” to navigation.

71. ATOLLS Sometimes known as a coral atoll, is a ring-shaped coral reef including a coral rim that encircles lagoon partially or completely. There may be coral island or cays on the rim.