floodplain presentation

introduction of geomorphology, definition of floodplains, its types and its important.

1.   BANGALORE UNIVERSITY ASSIGNMENT ON GEOMORPHOLOGY M.SC APPLIED GEOLOGY 1 ST SEMESTER (2017-18)  SUBMITTED BY- RUPANKAR RAJKHOWA   BANGALORE UNIVERSITY

2. CONTENT INTRODUCTION FLUVIAL DEPOSITIONAL FEATURES ALLUVIAL FANS AND CONES PIEDMONT ALLUVIAL PLAINS FLOOD PLAINS DELTA NATURAL LEEVES FLUVIAL TERRAIN FLOOD PLAINS ECOLOGY INTERACTION WITH SOCIETY FLOOD PLAIN IN INDIA REFERANCES

3. INTRODUCTION The word geomorphology (Greek, Geo – earth, morph – form/shape and logos- scientific study) is used for a systematic scientific study to explains the exterior from or features of the earth surface. Mc Gee (1888-96) defined geomorphology as a ‘genetic study of topographic forms’. Geomorphology is based on the analysis of geological facts ( agencies, processes and factors) that are continuously shaping the earth’s surface. Geomorphology can not only describe the mechanism of development of landforms but also the agencies that are responsible for the processes.

4. FLUVIAL The fluvial processes are associated with rivers and streams and the deposits and landforms created by them FLUVIAL PROCESSES It included the motion of sediments and erosion or deposition on the river bed. The river carries significant quantities of sediments, this material can act as tools to enhances wear of the bed ( abrasion). Sometime the fragments that themselves are ground down, becoming smaller and more rounded ( attrition) Sediments in rivers is transported as either bed load ( the coarser fragments which move close to the bed ) or suspended load ( finer fragments carried in the water). There is also a components carried as dissolved material. By draining the land surface they dispose the superfluous water brought by precipitation.

5. They are responsible for much of the denudation of the land surface over large parts of the earth. Area where more particles are dropped are called alluvial/floodplain and the dropped particles are called alluvium. Examples :- ‘Mississippi River’ annually carries 406 millions tons of sediments, ‘Huang He’ carries 796 millions tons of sediments . ‘ Po River’ Italy 67 millions tons of sediments . Ganga- Brahmaputra- Meghna annually carries 38,897 lakh sediments. Indus annually carries 23,56 lakh sediment

6. A TYPICAL RIVER SYSTEM HAS THREE SUBSYSTEM C ollecting S ystem Transporting System Depositing system

7. DEPOSITION BY RIVER Wherever the velocity of the river water is reduced, some of the load is deposited; a decrease in turbulence may also bring about the same effect. The heavier and coarser materials are first deposited followed by fine silt and mud. It is not only confined to the lower course, it can even occur on the upper course, but here it is temporary and can be removed sooner or later.

8. CAUSES OF DEPOSITION Break in slope : where the streams leaves the hills and enters a plain. Widening of valley floor allows flooding to occur. Contact with quiet water when swift flowing streams enters quiet waters or lakes. Where stream peters out as in arid and desert regions causing a decrease in river energy and allowing sediments to be laid. Where rivers debouch into the sea.

9. DEPOSIOTIONAL FEATURES Alluvial Fans and Cones Piedmont Alluvial Plain Flood Plain Delta Natural levees Fluvial terrain

10. FLOOD PLAINS It is a depositional features. Floodplains is an alluvial surface adjacent to a channel that is frequently inundated. Its size is generally related to the discharge of the river. The Three ways in which Floodplains may be formed- By vertical accretion By Lateral accretion By island formation and channel abandonment

11. VERTICAL ACCRETION When the stream is at the brink of overflowing (flooding) the state of flow of the river is known as bank full. If the flood spills over, there is overbank. The large rivers, with gentle gradient and a predominantly suspended load , flood they spread out both sides depositing a thin sheet of fine sediments material previously carried in suspension . It is the process in which the river Deeping downwards.

12. LATERAL ACCRETION The rivers naturally tend to flow in a sinuous pattern, this I because of the turbulent flow of water and irregularity or bend in the channel, which deflects the flow of water to the opposite bank. The forces of water that strikes the streams bank and leads to erosion, under cutting which initiate small bends in the river channels. With time due to the continues strike of the current it lead to growth of bends and known as MEANDERS BEND . On the side of the meanders the velocity is minimum so some sediments load is deposited. since there deposit occur in the point of the meanders is called POINT BAR DEPOSITES . Erosion on the outside of the meanders and depositional on the inside of meanders it helps the meanders to migrate laterally. Lateral accretion of this point bar result in floodplain formation.

13. ISLAND FORMATION AND CHANNEL ABANDOMENT Island formation and abandonment of channel are commonly associated with BRAIDING. Due to lack of competence and capacity, the load that the river carried is dumped in the mid- channel to form island. As the river continuously shifting, the side channels on the landward side become progressively filled with sediments until they are abandonment and it get incorporated into the floodplain.

14. FLOODS PLAINS CHARACTERISED BY MANY DISTINCTIVE FEATURES THAT INCLUDE :- LEEVES ( ‘lever’ – to raise) are ridges lying parallel to the streams channel. This are formed by rivers in times of flood when overbank flow causes a decrease in streams velocity after it has left the confining channel walls. CREVASSE SPLAY it is a sedimentary fluvial deposit which forms when a stream breaks its natural or artificial levees and deposit sediments on a floodplains. Once the levees has been reached the water flows out of its channel the water spreads onto the flood plain sediments will starts to fall out of suspension as the water loses energy, The resulting deposition can create graded deposits. BACKSWAMPS the low lying floodplain adjoining a natural levee may contain marshy areas called back swamps. BAYOU is a body of water typically found in a flat, low lying area and can be either an extremely slow- moving streams or rivers or a marshy lake or wetlands. YAZOO STREAM is a geologic and hydrologic term for any tributary stream that runs parallel to, and within the floodplain of a large river for considerable distance, before eventually joining it.

15. OX BOW LAKE it is a U shaped body of water that forms when a wide meander from the main stem of a river is cut-off, creating a free- standing body of water. This landforms is so named for its distinctive curved shape, resembling the bow pin of an oxbow. Its form when a river creates a meander, due to the river’s eroding the bank through hydraulic action, abrasion and erosion. After a long period of time, the meander becomes very curved, and eventually the neck of the meander becomes narrower and the river cuts through the neck during a flood, cutting off the meander and forming an oxbow lake. E.g. ‘KANWAR LAKE BIRD SANCTUARY’

16. FLOODPLAINS ARE OF TWO BASIC TYPES CONVEX FLOODPLAINS – Are convex in cross section i.e. the land slopes away gently from the river bank to the sides of the valleys e.g. – Tigris , Mississippi,Ganga FLAT FLOODPALINS – A large majority of river plains are flat or gently concave in cross section. Natural levees is inconspicuous or absent and the alluvial flat rise very gently to the outer margins of the floodplains

17. ECOLOGY Floodplains can support particularly rich ecosystem, both in quantity and diversity. Tugay forests form an ecosystem associated with floodplains, especially in central Asia. a floodplains can contain 100 or even 1000 times as many species as rivers. Wetting of the floodplains soil release an immediate surge of nutrients: those left over from the last flood, and those that result from the rapid decomposition of organic matter that has accumulated since then. It has importance because of storage and conveyance, protecting of water quality and recharge of ground water. This makes floodplains particularly valuable for agriculture and support forest and livelihoods.

18. RIVERINE FLOODPLAINS These riverine floodplains typically flood during the springs, but are subject to periodic flooding due to excessive rainfall. The floodplains brings erosion and deposition of soils and can determine considerably the shape of the floodplain, the depth the composition od soil, the type and density of vegetation, the presence and extent of wetlands, richness and diversity of wildlife, and the depth of ground water. COASTAL FLOOPLAINS Marshes, near-shore ocean bottoms, beaches, bays costal dune lakes, tidal flats and estuaries are all components that make up the costal floodplain. They recognised for their importance to estuarine and marine fisheries. Estuarine wetland are important for breeding, nursery, and feeding grounds for marine fisheries and are important to waterfowl and other wildlife.

19. INTERACTION WITH SOCIETY Historically many towns have been built on floodplains, for number of reasons :- (1) Access of freshwater (2) The fertility of floodplain land for farming (3) Cheap transportation, via river and railroads, which often followed rivers (4) Ease of development of flat land. River flood has been one of the worst natural disaster In history – Particular in – Yellow river in china the world natural disaster in 1931 china flood and 1887 flood killed millions of people respectively. In the united states the FEDERAL EMERGENCY MANAGEMENT AGENCY (FEMA) manages the NATIONAL FLOOD INSURANCES PROGRAM ( NFIP). The NFIP offers insurances to properties located within a flood prone area, as defined by the FLOOD INSURANCE RATE MAP (FIRM) which depicts various flood risk for a community.

20. FLOODPLAINS IN INDIA THE GANGA BASIN :- The ganga basin gets flooded mostly in the northern part by its northern tributaries. The badly effected states of ganga basin are West Bengal, Bihar and Uttar Pradesh The Yamuna famous for flooding Haryana and Delhi. In West Bengal like Mahayana, Bhagirathi, Damodar etc. causes flood because of tidal effect and insufficient river channels. BRAHMAPUTRA AND BARAK BASIN :- The river banks of Brahmaputra and Barak get flooded due to the surplus water found in the Brahmaputra basin and Barak basin. This rivers along with their tributaries flood the northern states like West Bengal, Assam and Sikkim. Jaldakha, Testa and Torsa in northern West Bengal and river in Manipur often overflow the Bank.

21. CENTRAL INDIA AND DECAN RIVER BASINS :- Southern and Centre India observes flood caused by Narmada, Godavari, Tapi, Krishna and Mahanadi even floods coastal region of Andhra Pradesh, Orissa and Tamil Nadu occasionally

22. AVERAGE ANNUAL FLOOD DAMAGE ( 1953- 2001) STATE DAMAGE AREA LIABLE TO FLOODS( million Ha) Total Damage Rs 13,400 millions Area Affected 8.11 million hectare Crop Area Affected 3.57 million hectare Human Lives Lost 2057 Nos Cattle Lost 95,000 Nos India receives an annual rainfall of 400 millions hectare meters, of which 75 percent is received in four months. Flood generally follow, bringing devastation with them. As death tolls mount, damage reaches unimaginable scales . 12.5% area of the country covers flood prone area.

23. REFERANCES The earth Dynamic surface – A textbook of Geomorphology - K . Siddhartha Principles of Geomorphology – 2 nd Edition - William D. Thornbury Principles of Engineering Geology - K.M Bangar Textbook of Physical Geology - G.B Mahapatra www. Wikipedia.com www.britinica.com