Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 1 Cross Drainage Works 1.Aqueducts: If the bed level of the channel is higher than H.F.L. of the drain, the structure is an aqueduct. Otherwise, the structure is either syphon or culvert. 2.Culvert If there is no restriction downstream, the structure will have two slopes S1 and S2, then, the structure will be a culvert. 3.Syphon If there is any restriction downstream the structure will have three slopes, therefore the structure is a syphon. Hydraulic Design of Syphon Design a syphon with the following data a.Canal Discharge= 40 cumec Bed width= 18 m Full supply depth= 2.1 m Bed level= 250 m Side slope= 1 H: 1 V b.Drain Flood discharge= 100 cumec Bed level= 251.8 m Depth= 1.45 m H.F.L. = 253.25 m 16 m44.5 m8 m RoadwayRoadway Drain Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 2 Design 1.Drainage waterway Laceys Formula 4.83 ,wetted perimeter4.83 10048.3P Q Pm= === Total length of barrels 8 44.5 1668.5 70m=+ += = Provide bed width of the drain at crossing 44.5m =High flood level of the drain= 253.25 m 2.Canal waterway Velocity of approach( )2400.91.5 2.1 18 2.1Qm sA= = =+ Maximum fluming is 40%,0.4 18 7.2m =Let the canal waterway be reduced from 18 m to 7.3 m such that two barrels each 3.5 m with 0.3 m thick wall. Let the height of the barrel = 2.5 m ( )( ) ( )402.29 2 ~ 33.5 2.5 22.290.46 1 1, 0.4 ~ 0.69.81 2.5QV m s V m sAVFr FrgD= = = = = = = < < The flow is subcritical in the barrel. 3.Head loss and bed levels at different sections: Provide 2 in 1 splay in contraction, and 3 to 1 splay in expansion, and 3 in 1 splay in expansion: Length of contraction18 7.32 10.72m= =Length of expansion18 7.33 16.052m= =At section 4 2 20.9Velocity head 0.0412 2 9.81aaVh mg= = = R.L. of bed = 250 m 3.5 m 2.5 m 0.3 m Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 3 R.L. of water surface = 250+2.1=252.1 m R.L. of T.E.L. = 252.1+0.041 = 252.141 m At section 3 Provide water depth= 3 m Area of section23 7.3 21.9m = = ( )22340Velocity 1.8321.91.83Velocity head 0.172 2 9.81Qm sAVmg= = == = = Loss of head in expansion from section 3 to section 4 2 2 2 23 421.83 0.90.3 0.0392 2 9.81V VK mg| | | | = = = ||\ . \ . El. of T.E.L. at section 3 252.141 0.039 252.18m = + =R.L. of water surface 252.18 0.17 252.01m = =R.L. of bed 252.01 3 249.01m = =Head loss through barrels21 212L Vf fR g| |= + + |\ . where, f1= constant for syphon mouth =0.08 for bell mouthed syphon 21bf aR| |= + |\ . where a and b are constants depending on the material of the surface of barrels.For cement plaster, a = 0.00316 and b = 0.1. ( )2 3.5 2.53.5 2.5 2 2ARP = =+ 20.10.00316 1 0.0360.729f| |= + = |\ . Assume length of syphon barrels L= 70 m ( )22.29701 0.08 0.00360.729 2 9.810.381Lhm| |= + + |\ .= At section 2 Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 4 R.L. of T.E.L. R.L. of T.E.L. @ section 3 + head loss through barrels252.18 0.381 252.561m== + = R.L. of water surface 252.562 0.17 252.39m = =R.L. of bed 252.39 3 249.39 say 249.40 m m = =At section 1 2 22 112 2 in contraction transition21.83 0.90.2 0.0262 9.81LV Vh Kgm| | = |\ .| | = = |\ . R.L. of T.E.L. 252.561 0.026252.587m= += R.L. of water surface 252.587 0.041252.546m= = R.L. of bed 252.546 2.1 250.446m = = Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 5 4.Transitions Because the depth is varying through the transition, Metras and Chutervedis formulae for transitions are not applicable, therefore Hinds method shall be used. The expansion transition is explained in more details, please refer to section 4.b. a.Contraction transition 211w.s. @ sec.1-w.s. @ sec. 22252.546 252.40.0732length of transition 10.75.352 2y C xymx m=== == = = Substitute y1 and x1 in the equation to find C ( )220.073 5.350.00260.0026CCy x=== Contraction Transition [1][2][3][4][5][6][7][8][9][10][11] Dist.y El. of W.S.El. of T.E.L. Velocity head Velocity Side slope Area Bed level DepthBed width (m)(m)(m)hv (m)V (m/s)sA (m2)(m)D (m)B 0.0026x2 Linear Interp. [4]-[3](2g hv)1/2 Linear Interp. [3]-[9]A/D - s D 0.000.0000252.400252.5000.0171.830:121.86249.403.07.30 2.507.53 5.359.06 8.0014.56 10.700.0000252.546252.5870.0400.901.5:144.44250.452.118.00 b.Expansion transition ( )1112 22252.1 252.010.045216.058.02520.0458.0250.0007y mx myCxy x= == == == Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 6 Pucca Floor Expansion Transition [1][2][3][4][5][6][7][8][9][10][11] Dist.y El. of W.S. El. of T.E.L. Velocity head Velocity Side slope Area Bed level DepthBed width (m)(m)(m)hv (m)V (m/s)sA (m2)(m)D (m)B 0.0007x2 Linear Interp. [4]-[3](2g hv)1/2 Linear Interp. [3]-[9]A/D - s D 0.000.0000252.010252.1800.1701.8260:121.86249.013.007.30 3.000.0063252.016252.1730.1571.7530.28:122.73249.202.827.29 6.000.0252252.035252.1650.1301.5960.56:125.48249.382.668.09 8.020.0450252.055252.1610.1061.4420.75:128.37249.502.569.16 10.000.0252252.075252.1560.0811.2620.93:131.75249.632.4410.71 13.000.0063252.094252.1500.0561.0511.21:138.10249.812.2813.92 16.050.0000252.100252.1400.0400.8861.5:144.44250.002.1018.00 5.Pucca floor Provide pucca floor in half the transition length in the upstream and 3/4th the length of the expansion transition in the downstream. Length of pucca floor u.s.10.75.35say 6.02m m = = 7.30 7.30 8.09 9.16 10.7013.92 18.00 0368.02101316.05 mx Bed width (m) 16.05 8.025 y1 252.1 w.s. El. 252.01PROFILE PLAN Bed level Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 7 6.Uplift pressure on the barrel floor and pucca floor a.Static uplift pressure i.At the bottom of barrel floor Level of bottom of barrel floor ( ) 251.8 0.6 0.3 2 2.5 248.1m = + + =Static head 250 248.1 1.9of water m = =ii.At the downstream end of barrel Floor level 249.01m =Assume floor thickness 249.01 1.5247.51m= = Static head 250 247.51 2.49of water m = =b.Seepage head on the barrel floor and the pucca floor Seepage head H.F.L. in the drain W.T. in the region (canal bed level)253.25 250 3.25m== = Total seepage path( )( )130.6 2 0.3 2 2.5 18 13 11.3m= + + + + = i.At the bottom of barrel floor Seepage path to bottom of barrel floor 0.6 2 3.1 1 4.3m = + =113.25, 2.01of water11.3 4.3 11.3HH m = = Total uplift in the barrel 1.9 2.013.91of water m= += ii.At d.s. end of barrel floor 4.3 6.97 Total seepage length = 11.3 m 3.25 H1 H2 Max. Seepage head Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 8 Seepage path80.6 2 3.136.97m= + += 223.25, 1.25of water4.3 11.3HH m = =Total uplift 2.49 1.25 3.74of water m = + =Floor thickness3.741.7say 2.02.2m m = = The remaining length of transition shall be provided with0.8 0.8 0.6 m m m C.C. blocks over 0.6 m inverted filter. 4 rows of blocks resting on 1.2 m deep toe wall at ends. Hydraulic Structures Hydraulic Design of SyphonFebruary 1, 2011 9