TRAINING PROGRAMME ON ENGINEERING DESIGNS-CANAL STRUCTURES GENERAL DESIGN PRINCIPLES Canal outlets and Modules BY ROUTHU SATYANARAYANA CHIEF ENGINEER (Retired.) FORMER ADVISOR, GOVERNMENT OF A.P

Cross Masonry Works- Modular Outlets  Definition: i.Off –take sluices: It is a small structure which admits water from the parent canal to a distributing channel or to a water course of a filed channel. Water distribution system is classified as: 1. Supply System or Conveyance System: Discharge >5.66 cumes(200 c/s) and perennial and always gated. 2. Distributary System: Discharge < 5.66 cumecs (200 c/s), runs on and off system, No gates, Water will be distributed proportionately through Modules (APM or OFM). ii. Gated off takes: Square or Rectangular openings or pipes Sill levels will be kept at bed level or above bed level of parent canal depending on the % discharge of the OT with Parent canal discharge:

Cross Masonry Works- Modular Outlets  Basic Data: Site plan with contours showing the flow direction. Hydraulic particulars both upstream and downstream of: Parent canal. The distributaries. Cross sections of the parent canal and the distributor. Levels, such as BL, FSL, TBL, GL, shall be marked on the CS. TPs Particulars, taken up to hard strata or to a minimum depth of 2m below CBL or ground level which ever deeper with soil classification. Bearing capacity of the foundation strata.

Cross Masonry Works- Modular Outlets Sill levels will be kept at bed level or above bed level of parent canal depending on the % discharge of the OT with Parent canal (PC) discharge: % DischargeHeight of sill of OT above CBL of PC when FSD in PC in m to 1.22below %0.075 …… 10% to 15% … 5% to 10% % to 5% <2% Minimum size of Hume Pipe:: 300mm Main and branch canals: 900mm Distributory : 230mm for Q=14.15 to 2.83 cumecs and 150 mm for Q < 2.83 cumecs

Cross Masonry Works- Modular Outlets  Important Guidelines: Recommended Loss of head at structures: CM&CD worksHead loss in mm Cross Regulator75 to 150 Aqueduct75 to 150 Canal Syphon 75 to 150 Measuring device 75 BridgesNot permitted

Cross Masonry Works- Modular Outlets  Vent way: Vent way calculated from the formula: Q the discharge in cumecs = C.A.(2gH) 1/2 where C = a constant : 0.62 for Square or Rectangular opening 0.75 for circular opening A = Area in Sq. m H = Driving head in m Q for Rectangular a Square opening = A (H) 1/2 Q for Circular opening = A (H) 1/2

Cross Masonry Works- Modular Outlets  Definition: A device built at the head of the water course connecting the distributaries to control the flow of water. It measures the discharge passing through.  Requirement: Structurally strong, With out any moving parts, Difficult for the cultivators to interfere and if so easily detectable, Work efficiently for small working heads, Can draw fair share of silt and economical.  Classification: Modular out lets: It is independent of water levels in the parent canal and the water course with in reasonable working limits (minimum working head). a.With moving parts, difficult to construct and costly b.With out moving parts called as Rigid Modules. Non-Modular out lets: Semi-Modular outlets or Flexible modules Rigid modules and modular out lets

Cross Masonry Works- Modular Outlets.  Semi-Modular outlets or Flexible modules Open Flume Outlet (OFMs) Crump’s Adjustable proportionate Module ( Crump’s APM) Adjustable Orifice Semi module (AOSM) Pipe Semi Module

Cross Masonry Works- Modular Outlets  Non-Modular outlets: It is a pipe outlet with one end submerged in water course fixed horizontally at right angle to the flow.. Consists of circular or rectangular opening and pavements. Discharge widely varies with the change of water level either in the canal or the water course. Discharge Q in cumecs = CA(2gH) 1/2 (Q= K A H 1/2 for pipe sluices, K being 6 for rectangular and 5 for circular in FPS system) Where, A= cross sectional area of the pipe in sq. m. C= Coefficient = 1__ [d/f(L+1.5d/400f)] 1/2 2 x 10 5 H= difference in water levels, f = coefficient of fluid friction, and 0.01 for clear and encrusted iron pipes and for earthenware pipes. L = length of pipe in m d = diameter of the pipe in cm Drowned pipe outlet and Masonry sluice comes under this category.

Cross Masonry Works- Modular Outlets  Semi-Modular outlets: Non-Modular outlet works as Semi-Modular outlet if the exit end of the pipe is made to discharge with a free fall. In this case working head H is the difference between water level in the parent channel and the centre of pipe. It is independent of water level in water course up to minimum working head. Discharge increases with increase in the water levels in the distributary's. Pipe outlets, venturi flumes, open flumes and orifice semi modules are the examples.  Open Flume out let (OFM): A smooth wear with a throat constricted sufficiently to ensure velocity above critical, and long enough to ensure that the controlling section remain with in the parallel throat at all discharges up to the maximum. A gradually expanded flume is provided at the outfall to recover the head. The entire work can be built in brick, but the controlling section is provided with cast iron or steel bed and check plates. Throat width Bt never kept less than 6cm hence it is necessary to raise the crest level of the out let much above bed level. Working head required with a 1 in 5 glacis and side walls splaying at 1 in 5 is 20% of depth of water above the crest of out let. Formation of hydraulic jump makes the out let independent of water level in the out let channel

Cross Masonry Works- Modular Outlets  Open Flume out let (OFM): Q in Cumecs = K Bt H3/2 Where K = a constant depending upon the width of the flume Bt = throat width of the weir (minimum 6 cm) For Bt, 6 cm to 9 cm K=1.6 9 cm to 12 cmK= 1.64 > 12cmK= 1.66 H = head over crest in m. It is most suited to tail cluster and proportionate distribution.  Adjustable orifice Semi Module (AOSM) An orifice provided with gradually expanding flume on the d/s side of the orifice. The flow through the orifice is super critical, resulting in the formation of hydraulic jump in the expanded flume portion. The formation of jump makes the discharge independent of water level in the out let channel.

Cross Masonry Works- Modular Outlets  Crump’s Adjustable Proportionate Module or adjustable Orifice Semi-Modules ( APM): Most commonly used module. CI base, CI roof block and check plates on sides nucleus around masonry. It can not be tampered and can conveniently adjusted at a very small cost. Setting of d/s wing wall of approach, W = k(q/Q){Bu+D/2} Where,k= ratio between mean velocities of distributory and the water course q= discharge in cumecs of the water course Q= discharge in cumecs in the distributory Bu= bed width of the distributor u/s of outlet D= depth of water in the distributory Q in cumecsk to to >

Cross Masonry Works- Modular Outlets  Pipe Semi-Module (PSM): Pipe out lets discharging into atmosphere is the simplest and the oldest type of the flexible out let. The discharge is independent of the water level of the out let channel.

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