PowerPoint Presentation

HYDRAULICS

1HydraulicsTeaching ObjectivesLearn basic conceptsWater propertiesOpen channel flowCulvert (or Pipe) flowVariation in hydraulic conditionsTemperature and ice effectsFlow measurements

22Hydraulics DefinitionWikipedia: Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties.

From Elementary Fluid Mechanics, Vennard and Street, 1975. Because of the conflict between theory and experiment, two schools of thought arose in the treatment of fluid mechanics, one dealing with the theoretical and the other with the practical aspects of fluid flow. In a sense, these two schools of thought have persisted to the present day, resulting in the mathematical field of hydrodynamics and the practical science of hydraulics. 3DESCRIPTION OF HYDRAULICS SECTION, St. Paul District

Responsible for hydraulic engineering associated with the planning, design,construction, operation, and maintenance for various civil works water resources programs and projects.

The water resources areas covered include navigation, flood risk management,ecosystem restoration, dam and levee safety, bank stabilization, flood reconnaissance.

The work includes: modeling and design for levees, bank stabilization, channel improvements, interior flood control, habitat projects, and hydraulic structures collecting and analyzing hydraulic and sediment transport data ice reconnaissance and data collection reconnaissance and support for flood emergencies support to periodic inspections at locks and dams wetlands permit reviews dredge material management coastal engineering agency technical reviews44This is a more practical definitionWater Properties

Heavy - 1 cubic foot weighs 62.4 lbs Gasoline weighs 42.5 lbs/ft3Rock weighs 110 lbs/ft3Concrete weighs 165 lbs/ft3Wood: White Oak = 48 lbs/ft3 White Pine = 26 lbs/ft3Temperature Affects: Important in lakes and reservoirsWhy does something float?The laws of buoyancy (Archimedes Principle, 250 BC) and floatation are usually stated:A body immersed in a fluid is buoyed up by a force equal to the weight of fluid displacedA floating body displaces its own weight of the liquid in which it floats55( bring 1 cu ft cardboard box and a bucket of known volume and scale. )Throughout this talk I used the English System of Measurement as opposed to the Metric System

Water PropertiesFlows from high energy to lower energy zonesFollows the path of least resistance

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Highway 32New Channel Eroded During 2002 FloodDam6Water PropertiesWater Seeks its Own levelIf its at elevation 100 on one side of a dam or levee, it wants to be the same elevation on the other side. Incompressible- So It Transmits Energy WellLiquid at normal temperatureHeating to 212 F (boiling point) raises the vapor pressure to atmospheric pressure and liquid turns to gasLowering the pressure (for instance in a pipe or on a spinning propeller) can cause gas formation at lower temperaturesCavitation: Low pressure conditions results in liquid to gas and then collapse back to liquid which plucks metal off turbine blades and concrete off spillways77Water PropertiesDensity doesnt change significantly with ambient temperature range.1.9385 slugs/ft3 at 32 F 1.9388 slugs/ft3 at 40 F (water is heaviest)1.9348 slugs/ft3 at 70 F (0.2% lighter than at 40 F) This means we can usually ignore density changes in flowing rivers because of mixingBut in lakes these slight density differences result in thermal stratification

88Illustrate Temperature profile in a lake.Water at RestPressure (P) Increases with DepthP = 62.4 lbs/ft3 x depth ftTotal Force acts at 2/3 total depth99Hydrostatic Pressure.Water in MotionWater moves from higher to lower energyGravity (or downhill) flowPumps can be used to increase the energy levels to move water to a higher level or to get it over a barrierThe flow of water is resisted by the boundary roughness. This is true in channels and in pipes

10Downstream FlowResistanceChannel BottomFlowDirectionWater in MotionRiver BankRiver BankAvThe flow rate (Q) of water moving past a cross section is equal to the area (A) of the cross section multiplied by the velocity (v)

Q (ft3/s) = A (ft2) * v (ft/s)

Flow rate is also called discharge andcfs, or cubic feet per second, is used to designate flow1111cfs = cubic feet per second = ft3/s

Ways to describe water in motionThe next few images attempt to define common terms that H&H people use when describing the movement of water.In a multi-discipline team setting you dont need to be an expert in H&H, but you should understand some of the lingo.12PrimaryFlowDirectionSecondary CurrentOne-, Two-, and Three-Dimensional FlowsxyzTruth is that when water is flowing it is almost always 3-dimensional.But that is difficult to quantify.So we like to simplify, if we can, to 2-dimensional or 1-dimensionalin our descriptions, analysis, and modeling.River BankRiver Bank1313Make sure everyone understands what this diagram is supposed to represent

One-, Two-, and Three-Dimensional FlowsWhen planners talk to hydraulic modelers they will hear the terms 1-D, 2-D, 3-D flow and models.In a one-dimensional flow, the change of fluid variables (velocity, temperature, etc.) in one direction dominates over the change in the other two directions.In two- and three-dimensional flows, the change in fluid variables is important in multiple directions.Coefficients, model calibration, and past experience are used to account for simplifying assumptions.14Change of Flow with Respect to Time

- no change: steady- changing: unsteady1515Steady Flow ExampleRelease at a spillway notch with a constant headwater.

Q = constant

1616The headwater is maintained at elevation 639.0 (+ or 0.2) through the operation of gates elsewhere in this system. This means that the notches provide a nearly constant flow of 50 cfs to downstream receiving waters.Unsteady Flow ExampleMissouri River Flow hydrograph at DecaturQ varies with time17

17Change of Flow Conditions with Respect to Spatial Position?

1818Varied Flow ConditionsDamM1 Backwater ProfileAbrupt drop, downstream channelization M2 Backwater ProfileFlow along these profiles is gradually varied (ie. the flow characteristics change slowly in the upstream to downstream direction). Right at the abrupt drop in the lower profile however the flow characteristics change vary fast. This is known as rapidly varied flowFlow DirectionFlow DirectionChannel BottomChannel Bottom1919The triangle represents water surface elevationChange in modeled velocity with space and discharge

2020These computer generated images show velocity magnitude for a low flow (left image) and high flow conditions. In both cases, the discharge conditions were assumed to be steady.Change in Velocity Across River Valley During a Flood

21Specific Energy (Open Channels)For open channels, the specific energy can be defined as E = y + v2/2g, where y is the depth of water above the channel bed, v is the flow velocity, g is the acceleration of gravity.

22Downstream FlowChannel Bottomyv2/2gNormal Depththe depth for which available energy and energy expended are in balanceDownstream FlowResistanceChannel Bottom23Seeking Normal DepthDamM1 Backwater ProfileAbrupt drop ordownstream channelization M2 Backwater ProfileGiven a sufficient channel length of unchanging section size,shape, slope, and roughness, depth tends to approachand/or maintain normal depth at some point upstream.Flow DirectionFlow DirectionChannel BottomChannel Bottom24Critical Depththe depth at which energy is the minimum possible for an open channel cross section of a given size and shape and a given flowthe VALUE of critical depth does not depend on roughness or slope, (only on discharge) yc = (q2/g)1/3 (Rectangular Channels)25EyycEmin25Quantifying critical depth is important for understanding open channel flow characteristics and for stilling basin design at hydraulic structures.Open Channel Flow RegimesSubcritical Flow:is deeper and slower than critical flowthis is what you usually see in rivers. relatively slow moving

Supercritical Flow:is shallower and faster than critical flow this is what you see in steep channels (rapids or flow over a dam)fast moving

Rio Puerco, NMSt. Anthony Falls, Miss R, MN2626Open Channel Flow RegimesHydraulic jumps occur when there is a transition from supercritical to subcritical flow

2727Rapidly varied flow. Very Turbulent. Super-critical flow changing to sub-critical flow.Biggest problem was getting this water (about 50 cfs) from this concrete structure, down to the river (which you can see in the upper left corner). It was a drop of only a four feet, but that is enough to create scour/undermining problems.Continuity Equation

Q = V1A1=V2A2( Flow = Velocity X Area )QA1V1A2V2Q122828For steady flow, if there are no inputs between section 1 and section 2, the discharge is the same at both sections. How do you calculate velocityWhat are some drivers (or parameters) that affect the speed that water moves at?What would a basic relationship look like?

v = ?FlowDirectionRiver BankRiver BankAv2929FlowDirectionPAVariable ListA = Cross Sectional Area (ft2)P = Wetted Perimeter (ft)R = A/P = Hydraulic Radius (ft)n = boundary roughness Q = Discharge (ft3/s)s = water surface slope = hl/Lv = velocity (ft/s)Mannings Equation (English Units)v = 1.49R2/3 s1/2 / n Q = 1.49AR2/3 s1/2 / nLhLRiver BankRiver Bank30Open Channel flow equations have been around for a long time.Wikipedia definition: The Manning formula, known also as the Gauckler-Manning formula, or Gauckler-Manning-Strickler formula in Europe, is an empirical formula for open channel flow, or free-surface flow driven by gravity. It was first presented by the French engineer Philippe Gauckler in 1867, and later re-developed by the Irish engineer Robert Manning in 1890.Can have open channel flow in culverts

30FlowDirectionPcAcSame Variable List (subscripts c and f)A = Cross Sectional Area (ft2)P = Wetted Perimeter (ft)R = A/P = Hydraulic Radius (ft)n = boundary roughnessQ = Discharge (ft3/s)s = water surface slopeMannings Equation with Floodplain FlowQtotal = Qchannel +QfloodplainQtotal = 1.49AcRc2/3 s1/2 / nc + 1.49AfRf2/3 s1/2 / nf AfPf31

Closed Conduits The area of flow is knownwhen it is flowing full though closed conduitflow is often in the open channel mode (e.g.Many culverts, storm sewers)

Open Channel: Free surface varies with time affecting area, channel area, depth,roughness, and slope. The relationship between all these variables, usually makesopen channel flow problems tougher to deal with.

Cross Sections3232Closed Conduits Roughness varies depending on material types, age, andcondition of pipe.

Open Channel: roughness varies depending on water depth, substrate size,density of vegetation, ..

Roughness (n-values)

3333Hydraulic Radius, R

R = A/P where A = area (ft2) and P = Perimeter (ft)

Square Pipe Flowing Full A = L2 P = 4L R = L2/4L = L/4 where L = side length (ft)

Circular Pipe Flowing Full A = D2/4 P = D R = D2/4 = D/4 D where D = diameter (ft)

Open channels where width is much greater than depth A = by P = b+2y R = by/(b+2y), but 2y 3 mg/L58Ice Damaged Groin, Trempealeau National Wildlife Refuge59As-built ProfileRoot River Ice Jam6061Lock and Dam 2, Debris, 2001 Flood62Wind-Driven Wave Damage During a Flood63Groundwater/Surface Water InteractionRivers re-charge groundwater table when river is highGroundwater recharges rivers when river is low Balance can be upset by dams, sediment deposition, groundwater pumping,At reach scale (ie. study area is a small reach of a much larger river or stream), groundwaters contribution to open channel flow is ignored.At a watershed scale, groundwaters influence to open channel flow can be significant 64Measuring FlowVelocity Price, ADCPDischargeStageWind wavesFlow characteristics through a structure65Measurement Options66Measurement Options67Hydraulic SurveysBoat with dual 50 HP motorsFathometerGPSLaptopADCP (Acoustic Doppler)Boat Safety Equipment and Training68~ The End ~6969