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# Irrigation (41-60)

Updated: Apr 9, 2020

41.The unit Iwdrograph due to a storm may be obtained by dividing the ordinates of the direct runoff hydrograph by direct runoff volume

42. The unit hydrograph of a specified duration can be used to evaluate the

hydrograph of storms of any duration

43. S-hydrograph is used to obtain unit hydrograph of shorter duration from longer duration,longer duration from shorter duration .

44. If two 4-hour unit hydrographs are staggered by 4 hours and added graphically, the resulting hydrograph will be 8-hour hydrograph with 20 mm

runoff

45. According to Dicken's formula for estimating floods, the peak discharge is

proportional to

where A is catchment area in square kilometres

46. The relation between probability (P) and recurrence interval (T) is given by

PT = 1

47. Dimensions of coefficient of transmissibility are

48. If d is the depth of the aquifer through which water is flowing, then the relationship between permeability k and transmissibility T is given by

T = kd

49. An artesian aquifer is the one where water is under pressure between two

impervious strata

50. A deep well has more discharge than a shallow well

51. A multipurpose reservoir is the one which is planned and constructed to serve

various purposes

52. The useful storage is the volume of water stored in the reservoir between minimum pool level and normal pool level

53. The water stored in the reservoir below the minimum pool level is called

54. For a flood control reservoir, the effective storage is equal to useful storage + surcharge storage -valley storage

55. Trap efficiency of a reservoir is a function of capacity/inflow ratio

56. The total capacity of a reservoir is 25 million cubic metres and dead storage is 5

million cubic metres. If the average volume of sediment deposition is 0.10

million cubic metre per year, then the usefulness of the reservoir will start

reducing after 50 years

57. The forces, which are considered for the analysis of an elementary profile of a

gravity dam under empty reservoir condition, are Self weight

58. When the upstream face of a gravity dam is vertical, then the intensity of water pressure at the water surface and at the base respectively will be 0 and wH

59. The uplift pressure on a dam can be controlled by constructing cutoff under upstream face,constructing drainage channels between the dam and its foundation,by pressure grouting in foundation

60. The uplift pressure on the face of a drainage gallery in a dam is taken as

two-third of hydrostatic pressure at toe plus one-third of hydrostatic pressure at heel