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1、Reservoirs,Spillways,&Energy Dissipators,CE154 Hydraulic DesignLecture 3,Fall 2009,1,CE154,Fall 2009,2,Lecture 3 Reservoir,Spillway,Etc.,Purposes of a Dam-Irrigation-Flood control-Water supply-Hydropower-Navigation-RecreationPertinent structures dam,spillway,intake,outlet,powerhouse,CE154,Fall 2009,
2、3,Hoover Dam downstream face,CE154,Fall 2009,4,Hoover Dam Lake Mead,CE154,Fall 2009,5,Hoover Dam Spillway Crest,CE154,Fall 2009,6,Hoover dam Outflow Channel,CE154,Fall 2009,7,Hoover Dam Outlet Tunnel,CE154,Fall 2009,8,Hoover Dam Spillway,CE154,Fall 2009,9,Dam Building Project,Planning-Reconnaissance
3、 Study-Feasibility Study-Environmental Document(CEQA in California)Design-Preliminary(Conceptual)Design-Detailed Design-Construction Documents(plans&specifications)Construction Startup and testingOperation,CE154,Fall 2009,10,Necessary Data,Location and site mapHydrologic dataClimatic dataGeological
4、dataWater demand dataDam site data(foundation,material,tailwater),CE154,Dam Components,Dam-dam structure and embankmentOutlet structure-inlet tower or inlet structure,tunnels,channels and outlet structureSpillway-service spillway-auxiliary spillway-emergency spillway,Fall 2009,11,CE154,Spillway Desi
5、gn Data,Inflow Design Flood(IDF)hydrograph-developed from probable maximum precipitation or storms of certain occurrence frequency-life loss use PMP-if failure is tolerated,engineering judgment cost-benefit analysis use certain return-period flood,Fall 2009,12,CE154,Spillway Design Data(contd),Reser
6、voir storage curve-storage volume vs.elevation-developed from topographic maps-requires reservoir operation rules for modelingSpillway discharge rating curve,Fall 2009,13,CE154,Reservoir Capacity Curve,Fall 2009,14,CE154,Spillway Discharge Rating,Fall 2009,15,CE154,Spillway Design Procedure,Route th
7、e flood through the reservoir to determine the required spillway sizeS=(Qi Qo)t Qi determined from IDF hydrograph Qo determined from outflow rating curve S determined from storage rating curve-trial and error process,Fall 2009,16,CE154,Spillway Capacity vs.Surcharge,Fall 2009,17,CE154,Spillway Cost
8、Analysis,Fall 2009,18,CE154,Spillway Design Procedure(contd),Select spillway type and control structure-service,auxiliary and emergency spillways to operate at increasingly higher reservoir levels-whether to include control structure or equipment a question of regulated or unregulated discharge,Fall
9、 2009,19,CE154,Spillway Design Procedure(contd),Perform hydraulic design of spillway structures-Control structure-Discharge channel-Terminal structure-Entrance and outlet channels,Fall 2009,20,CE154,Types of Spillway,Overflow type integral part of the dam-Straight drop spillway,H25,vibration-Ogee sp
10、illway,low heightChannel type isolated from the dam-Side channel spillway,for long crest-Chute spillway earth or rock fill dam-Drop inlet or morning glory spillway-Culvert spillway,Fall 2009,21,CE154,Sabo Dam,Japan Drop Chute,Fall 2009,22,CE154,New Cronton Dam NY Stepped Chute Spillway,Fall 2009,23,
11、CE154,Sippel Weir,Australia Drop Spillway,Fall 2009,24,CE154,Four Mile Dam,Australia Ogee Spillway,Fall 2009,25,CE154,Upper South Dam,Australia Ogee Spillway,Fall 2009,26,CE154,Winnipeg Floodway-Ogee,Fall 2009,27,CE154,Hoover Dam Gated Side Channel Spillway,Fall 2009,28,CE154,Valentine Mill Dam-Laby
12、rinth,Fall 2009,29,CE154,Ute Dam Labyrinth Spillway,Fall 2009,30,CE154,Matthews Canyon Dam-Chute,Fall 2009,31,CE154,Itaipu Dam,Uruguay Chute Spillway,Fall 2009,32,CE154,Itaipu Dam flip bucket,Fall 2009,33,CE154,Pleasant Hill Lake Drop Inlet(Morning Glory)Spillway,Fall 2009,34,CE154,Monticello Dam Mo
13、rning Glory,Fall 2009,35,CE154,Monticello Dam Outlet-bikers heaven,Fall 2009,36,CE154,Grand Coulee Dam,Washington Outlet pipe gate valve chamber,Fall 2009,37,CE154,Control structure Radial Gate,Fall 2009,38,CE154,Free Overfall Spillway,Control-Sharp crested-Broad crested-many other shapes and formsC
14、aution-Adequate ventilation under the nappe-Inadequate ventilation vacuum nappe drawdown rapture oscillation erratic discharge,Fall 2009,39,CE154,Overflow Spillway,Uncontrolled Ogee Crest-Shaped to follow the lower nappe of a horizontal jet issuing from a sharp crested weir-At design head,the pressu
15、re remains atmospheric on the ogee crest-At lower head,pressure on the crest is positive,causing backwater effect to reduce the discharge-At higher head,the opposite happens,Fall 2009,40,CE154,Overflow Spillway,Fall 2009,41,CE154,Overflow Spillway Geometry,Upstream Crest earlier practice used 2 circ
16、ular curves that produced a discontinuity at the sharp crested weir to cause flow separation,rapid development of boundary layer,more air entrainment,and higher side walls-new design see US Corps of Engineers Hydraulic Design Criteria III-2/1,Fall 2009,42,CE154,Overflow Spillway,Fall 2009,43,CE154,O
17、verflow Spillway,Effective width of spillway defined below,whereL=effective width of crestL=net width of crestN=number of piersKp=pier contraction coefficient,p.368Ka=abutment contraction coefficient,pp.368-369,Fall 2009,44,CE154,Overflow Spillway,Discharge coefficient CC=f(P,He/Ho,downstream submer
18、gence)Why is C increasing with He/Ho?HeHo pcrestCoDesigning using Ho=0.75He will increase C by 4%and reduce crest length by 4%,Fall 2009,45,CE154,Overflow Spillway,Why is C increasing with P?-P=0,broad crested weir,C=3.087-P increasing,approach flow velocity decreases,and flow starts to contract tow
19、ard the crest,C increasing-P increasing still,C attains asymptotically a maximum,Fall 2009,46,CE154,C vs.P/Ho,Fall 2009,47,CE154,C vs.He/Ho,Fall 2009,48,CE154,C.vs.,Fall 2009,49,CE154,Downstream Apron Effect on C,Fall 2009,50,CE154,Tailwater Effect on C,Fall 2009,51,CE154,Overflow Spillway Example,H
20、o=16P=5Design an overflow spillway thats not impacted by downstream apron To have no effect from the d/s apron,(hd+d)/Ho=1.7 from Figure 9-27hd+d=1.716=27.2P/Ho=5/16=0.31Co=3.69 from Figure 9-23,Fall 2009,52,CE154,Example(contd),q=3.69163/2=236 cfs/fthd=velocity head on the apronhd+d=d+(236/d)2/2g=2
21、7.2d=6.5 fthd=20.7 ftAllowing 10%reduction in Co,hd+d/He=1.2hd+d=1.216=19.2Saving in excavation=27.2 19.2=8 ftEconomic considerations for apron elevation!,Fall 2009,53,CE154,Energy Dissipators,Hydraulic Jump type induce a hydraulic jump at the end of spillway to dissipate energyBureau of Reclamation
22、 did extensive experimental studies to determine structure size and arrangements empirical charts and data as design basis,Fall 2009,54,CE154,Hydraulic Jump energy dissipator,Froude numberFr=V/(gy)1/2Fr 1 supercritical flowFr 1 subcritical flowTransition from supercritical to subcritical on a mild s
23、lope hydraulic jump,Fall 2009,55,CE154,Hydraulic Jump,Fall 2009,56,CE154,Hydraulic Jump,y1,V1,V2,y2,Lj,Fall 2009,57,CE154,Hydraulic Jump,Jump in horizontal rectangular channely2/y1=(1+8Fr12)1/2-1)-see figure y1/y2=(1+8Fr22)1/2-1)Loss of energyE=E1 E2=(y2 y1)3/(4y1y2)Length of jumpLj 6y2,Fall 2009,58
24、,CE154,Hydraulic Jump,Design guidelines-Provide a basin to contain the jump-Stabilize the jump in the basin:tailwater control-Minimize the length of the basin to increase performance of the basin-Add chute blocks,baffle piers and end sills to increase energy loss Bureau of Reclamation types of still
25、ing basin,Fall 2009,59,CE154,Type IV Stilling Basin 2.5Fr4.5,Fall 2009,60,CE154,Stilling Basin 2.5Fr4.5,Fall 2009,61,CE154,Stilling Basin 2.5Fr4.5,Fall 2009,62,CE154,Type IV Stilling Basin 2.5Fr4.5,Energy loss in this Froude number range is less than 50%To increase energy loss and shorten the basin
26、length,an alternative design may be used to drop the basin level and increase tailwater depth,Fall 2009,63,CE154,Stilling Basin Fr4.5,When Fr 4.5,but V 60 ft/sec,use Type III basinType III chute blocks,baffle blocks and end sillReason for requiring V60 fps to avoid cavitation damage to the concrete
27、surface and limit impact force to the blocks,Fall 2009,64,CE154,Type III Stilling Basin Fr4.5,Fall 2009,65,CE154,Type III Stilling Basin Fr4.5,Fall 2009,66,CE154,Type III Stilling Basin Fr4.5,Calculate impact force on baffle blocks:F=2 A(d1+hv1)whereF=force in lbs=unit weight of water in lb/ft3A=are
28、a of upstream face of blocks in ft2(d1+hv1)=specific energy of flow entering the basin in ft.,Fall 2009,67,CE154,Type II Stilling Basin Fr4.5,When Fr 4.5 and V 60 ft/sec,use Type II stilling basinBecause baffle blocks are not used,maintain a tailwater depth 5%higher than required as safety factor to
29、 stabilize the jump,Fall 2009,68,CE154,Type II Stilling Basin Fr4.5,Fall 2009,69,CE154,Type II Stilling Basin Fr4.5,Fall 2009,70,CE154,Example,A rectangular concrete channel 20 ft wide,on a 2.5%slope,is discharging 400 cfs into a stilling basin.The basin,also 20 ft wide,has a water depth of 8 ft det
30、ermined from the downstream channel condition.Design the stilling basin(determine width and type of structure).,Fall 2009,CE154,71,Example,Use Mannings equation to determine the normal flow condition in the upstream channel.V=1.486R2/3S1/2/nQ=1.486 R2/3S1/2A/nA=20yR=A/P=20y/(2y+20)=10y/(y+10)Q=400=1
31、.486(10y/(y+10)2/3S1/220y/n,Fall 2009,CE154,72,Example,Solve the equation by trial and errory=1.11 ftcheck A=22.2 ft2,P=22.2,R=1.01.486R2/3S1/2/n=18.07V=Q/A=400/22.2=18.02Fr1=V/(gy)1/2=3.01 a type IV basin may be appropriate,but first lets check the tailwater level,Fall 2009,CE154,73,Example,For a s
32、imple hydraulic jump basin,y2/y1=(1+8Fr12)1/2-1)Now that y1=1.11,Fr1=3.01 y2=4.2 ftThis is the required water depth to cause the jump to occur.We have a depth of 8 ft now,much higher than the required depth.This will push the jump to the upstream A simple basin with an end sill may work well.,Fall 2009,CE154,74,Example,Length of basinUse chart on Slide#62,for Fr1=3.0,L/y2=5.25 L=42 ft.Height of end sillUse design on Slide#60,Height=1.25Y1=1.4 ftTransition to the tailwater depth or optimization of basin depth needs to be worked out,Fall 2009,CE154,75,
