1. HYDROLOGY AND WATER RESOURCES ENGINEERING

2. FROM: BARAIYA HINAL(130340106004) RAVAL JANHAVI(130340106032) SHAH MANSI (130340106045) PANCHAL URVI (130340106053) PARMAR HETAL (120340106093)

3. TOPIC: FLOOD MANAGEMENT

4. Introduction: Any Flow which is relatively high and which overtops the natural or artificial banks in any reach of a river may be called a flood.

5. When the banks are overtopped, water spreads over the flood plain and thus cause damage to crops and property within the flood plain of the river.

6. It is not possible to prevent floods but is possible to prevent or reduce the damage due to floods by controlling the floods.

7. Thus flood control or flood management is defined as the prevention or reduction of the flood damage.

8. INDIAN RIVERS AND FLOODS: Almost all the rivers of india carry heavy flows during the monsoon when their catchments intense and heavy rainfall.

9. In upper reaches, where the rivers flow through mountainous terrain or undulating area, there is generally no overflow of the banks during high flows.

10. In lower reaches especially where the area is flat, the rivers overflow their banks and cause inundation of low-lying lands, submerge standing crops and property and disrupt communications.

11. In india, from the point of view of flood problem, the river can be grouped under the four categories: (1) Brahmaputra region (2) Ganga region (3)North-west region (4)Central India Decan region

12. 1.Brahmaputra region: The region covers the states of assam, northen portions of west bengal,manipur, tripura, arunachal pradesh and mizoram. The main rivers in the region are brahamaputra, barak and tributaries like tista, jaldhaka and mahananda.

13. The region very heavy rainfall from 110 cm to 640 cm per year. The main problems in brahamaputra regions are overspills, drainage congestion, bank erosion, landslides, aggradation and changes in the river courses.

14. 2.Ganga region: The region covers the states of uttarakhand, U.p., bihar, himachal pradesh, rajasthan, madhyapradesh, haryana, west bengal and delhi. The main rivers in yamuna, sone,gomti,kosi,ghagra.

15. The variations of rainfall in the slopes of the himalayas is from about 125 to 190 cm. more than 80% rainfall during the normal monsoon season, between july or october.

16. 3. North-west region: The region covers the states of jammu and rajasthan. The main rivers in the region are the indus and its tribulataries like sultej, beas, ravi, chenab, jhelum.

17. In the rest of the area, it decreases from about 60 cm in the east to less than 15 cm in the extreme western part of Rajasthan.

18. 4. Central india decan region: This region covers states like: andhra pradesh, karnataka, tamilnadu, kerala, orissa, maharastra, gujarat and parts of madhya pradesh.

19. The main rivers in the region are: The narmada, the tapi, the mahanadi, the godavari, the krishna and the cavery.

20. The annual rainfall over the western ghats can be as 500 cm, in the remaining area it varies from about 75 to 125 cm. generally stable, having sufficient capacities to carry flood waters, except in the delta areas.

21. Causes of floods: 1. intensity of rainfall: whenever there is heavy precipition over the catchment area is the main cause of the flood. The intensity of rainfall in the catchment area is the main cause of flood.

22. The intensity of rainfall in the catchment area is the main cause of flood. But if the rainfall is very heavy and the storm duration is longer, then the surface run-off will be incresed.

23. 2. Topography of the catchment: it is obvious that larger the size of the catchment more will be the flood. The catchment area with steep slope increases the run-off & increases the sediment inflow due to the high velocity of flow. while the catchment area with flatter slope reduces the run- off. The size, slope & shape of the catchment area directly affects the flow of the river.

24. 3.Sedimeutation of rivers & reservoirs due to unabated heavy heavy silting up will affect the flow the river. thus, the sedimentation of rivers & reservoirs are also responsible for the flood.

25. 4.Obstruction in the river flow: whenever there is a heavy landslide in the river, it may cause flood on the u/s side due to arrest of flow & consequent rise in water level. obstruction in or aggradation of river bed, changes in river course & convulsion resulting in flooding by the river flowing over land outside its channel.

26. 5.Contraction of river section: inadequate waterway at rail & road crossings will affect river flow. The water rises on the u/s side due to insufficient passage & thus the upstream area may get flooded.

27. 6.Inadequate cross drainage works: construction of cross drainage works reduces the depth of flow for the high flood.

28. 7.Other causes: (1) floods may be caused due to heavy melting of snow & ice.(2)in case there is breach of a dam, the reservoir water may rush towards the downstream side causing heavy flood for a short period. (3)sometimes because of earthquake it may so happen that the river bed is raised.

29. ALLEVIATION: The flood control measures can be classified broadly as structural & non- structural measures. Flood control aims at attempts to (1)modify the flood,(2)modify the susceptibility to flood damage, (3)modify loss burden &(4)bearing the loss or living with floods.

30. Structural mitigation measures: (1) storage reservoirs: it is the most effective measures of flood disaster mitigation measures. The modern reservoirs are mostly multipurpose. The reservoirs are formed on the upstream of the area to protected on the head reach of the river.

31. Hydrograph of floods without & with reservoir

32. The flood control reservoirs may be of two types:(a)Detention reservoirs: These are provided with outlets & spillways with adjustable gates which are operated according to the condition of down-stream area.

33. (b)Retarding reservoirs: These are provided with fixed, Ungated outlets which automatically regulate the outflow in accordance with the volume of water in storage. Flood flow is retarded & takes much time to discharge the flood storage water completely.

34. (2)Confining river flow by embankment: earthen embankments have been the principle methods of controlling flood as a short-term measure.

35. Earthen embankment for increased flood storage

36. (3)Channel improvement works: work performed to increase the discharge or velocity of stream or to decrease the stage & duration of flood is known as channel improvement.

37. (4)Diversion works: from the upstream side of the flood affected area a diversion channel is excavated to connect the river at the d/s area. A diversion channel with a regulator upstream of the important area is constructed.

38. Diversion works by a channel

39. (5)Flood wall: when no space is available for the construction of levee or when it is not suitable to construct the levee due to the site condition. There are masonry or concrete walls constructed just on the river bank.

40. (6)Flood ways: the low lying areas along the course of the known as floodways. The floodways is ordinarily used only during major flood, & the land in the floodway may be used for agriculture at other times.

41. (7) Runoff reduction by watershed management: different watershed management are(1)afforestation (2)contour farming (3)contour bunds (4)check dams (5)gullying (6)bank protection (7)diversion drains (8)strip cropping etc.

42. Non-structural mitigation measures: (1) flood plain zoning: Areas near the river are the most vulnerable for the flood hazard provided the areas are not a highland. There areas are used as parks, ground etc.

43. (2)Flood forecasting: the Emergency evacuation of the threatened area is one of the most effective means of reducing damage due to flood under certain circumstances. Temporary evacuation of persons & shifting the important property to safer places could be done before the flood arrives.

44. (3)Flood proofing: In cases where certain isolated units of high value are threatened by flooding, they may sometimes be individually flood proofed. In case of an industrial plant comprising building, storage yards, roads, etc. may be protected by a ring levee or flood wall.

45. (4) Mathematical modelling: in the flood disaster mitigation measures, mathematical model by computer can predict flood intensity & area of inundation whether it is flood in river or a flash flood due to dam break or dike failure.

46. LEVEES: A levees is an earth dyke or embankment. It is a sort of an earthen dam constructed along the river. Levees are usually built of materials excavated from borrow pits parallel to the levee line. When a city or agricultural district is to be protected a ring levee which completely encircles the area may be provided.

47. levees

48. Flood walls: A levee is an earth dyke or embankment, while a flood wall is usually of masonry or concrete. Flood wall are used in developed area where it is difficult to obtain enough land for the construction of levee. If there is a backfill on the land side of the wall, it acts as an earth retaining wall.

49. Flood walls

50. Flood ways: the low lying areas along the course of the river are known as floodways. flood receds in the river, the water stored in these depressions is permitted to flow back to the river. Floodways serve two functions in flood control.

51. Floodway

52. Flood damage analysis: there are two types of flood disaster: (a)Tangible losses: (1) damage of personal properties like building, furniture, etc.(2)loss of crops(3)loss due to disruption of trade, business etc.

53. (b)Intangible losses: (1)loss of human life & cattle.(2)loss of health due to diseases caused by flood.(3)loss caused by social distress.(4)snake bites & other physical & hardships.

54. THANK YOU