Sunday, January 5, 2014

GATE, PSUs - Hydraulics, Irrigation, water resource Engg. notes - part 7

Hello there,
How have you been? Here is the 7th part of our notes for preparation of GATE and other examinations related to Civil Engineering.

  • As compared to gravity dams, earthen dams requires less skilled labor.
  • The most suitable material for the central impervious core of a zoned embankment type dam is clay mixed with fine sand.
  • Seepage through embankments in the earthen dam is controlled by drain trenches.
  • Seepage through foundation in an earthen dam is controlled by providing impervious cut-off.
  • The flow of water after spilling over the weir crest in chute spillway and side channel spillway respectively are at right angle and parallel to weir crest.
  • The discharge passing over an Ogee spillway is given by CLH^(3/2) where, L is the effective length of spillway crest and H is the total head over the spillway crest including velocity head.
  • Co-efficient of discharge of an Ogee spillway depends on depth of approach and upstream slop and also on downstream apron interference and downstream submergence.
  • Ogee spillway is least suitable for earthen dams as compared to chute spillway, side channel spillway and shaft spillway.
  • In case of non-availability of space due to topography, the most suitable spillway is shaft spillway.
  • In case of chute spillway, the flow is usually super-critical.
  • For upstream face of an earthen dam, the most adverse condition for stability of slope is sudden draw-down.
  • If there are two canals taking off from each flank of a river, then there will be two divide wall and two under-sluices.
  • Generally the weir is aligned at right angles to the direction of the main river current because, it ensures less length of the weir, gives better discharging capacity and is economical.
  • The main function of divide wall is to separate the under-sluices from weir proper.
  • A divide wall is provided at right angle to the axis of the weir.
  • As compared to crest of the normal portion of the weir, the crest of the under-sluice portion of weir is kept at lower level.
  • Silt excluders are constructed on the river bed upstream of head regulator.
  • If h is the ordinate of hydraulic gradient line above the top of the floor and G is specific gravity of floor material, then the thickness of floor is given by the formula h/(G-1).
  • According to Khosla's theory, the exit gradient in the absence of a downstream cutoff is infinity.
  • The minimum size of stone that will remain at rest in a channel of longitudinal slope S and hydraulic mean radius R is given by 11 RS.
  • The ratio of average values of shear stress produced on the bed and the banks of a channel due to flowing water is greater than 1.
  • If the critical shear stress of a channel is Tc, the average value of shear stress required to move the grain on the bank is 0.75Tc.
  • A water shed canal avoid the cross drainage works.
  • A canal which is aligned at right angles to the contours is called side slope canal.
  • Garret's diagrams are based on Kennedy's theory.

All information is learned through books and practical exercises.

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