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【導(dǎo)讀】Rafael(Rafa)Muñoz-Carpena,I-A,PEReview2020-09. Hydrology. OpenChannelFlow. HydrologicCycle. Precipitation. Runoff. Weirflow. Orificeflow. Pipeflow. Spillwayflow. Channelgeometries. Manning’sequation. Youneedto:. Formsinclude:. Measureddirectly. Daily. Hourly. 15-minute. Continuous. TheissenPolygon. fromupperleft:65ac,150ac,55ac,140ac,constructionadded.Whybisectors?(65*+150*+55*+140*+215*+270*2.significantdigits.average,onceevery10years.
【正文】 ’ long with one 90176。 bend. The top of the inlet is 10’ above the bottom of the outlet. Develop the stagedischarge relationship assuming a free outfall. Weir flow Basic equation: Given 18” riser, length of weir is 2πr, or ’, so Orifice flow Basic orifice equation: Given 18” riser and assuming C’ of , Pipe flow Basic pipe flow equation: After looking up each parameter: StageDischarge Relationship Questions on spillway hydraulics? Open Channel Flow Flow through open channels is another important area to consider and review. Velocity and flow rate are usually calculated using Manning’s equation, which considers flow geometry, channel roughness and slope. Manning’s Equation Where: V= flow velocity in fps Rh = Hydraulic Radius in ft S = Energy gradeline slope in ft/ft (=bed slope for normal flow) n = Manning coefficient = conversion from SI to English units Hydraulic radius is the flow area divided by the wetted perimeter. Open Channel Flow – Channel Geometry Manning “n” values Example What is the flow rate for a rectangular finished (clean) concrete channel with a base width of 8’, channel slope of %, with a “normal” water depth of 2’? A: 140 cfs B: cfs C: 100 cfs D: 200 cfs Solution n is , Rh is 8*2 ./(2+8+2) ft, S is ft/ft, so V = ft/sec Q = V*A= ft/sec*16 . = 140 cfs Vegetated Waterway Design The design of a vegetated waterway is an iterative process, considering both capacity when the grass is unmowed and hence higher resistance to flow and stability when recently mowed and more susceptible to bed scour at high flow velocities. Fortunately, the EFM has tables of suitable channel dimensions. Design steps from EFH: Example A subdivision produces a peak runoff rate of 60 cfs from a 10yr24hr rainfall. A vegetated waterway with an average slope of 3% is to be planted with Kentucky bluegrass. The soil at the waterway site is easily eroded. The waterway will be constructed with a parabolic shape. What top width and depth are required (ignoring freeboard)? Choices A: 20’, 2’ B: ’, ’ C: 15’, ’ D: 12’, ’ Permissible Velocity Kentucky bluegrass on a 3% slope easily eroded soil can handle up to 5 fps. Resistance to flow Kentucky bluegrass has a C resistance when unmowed and a D resistance when cut to 2” height EFM table Reading the chart for 60cfs, V1 of 5fps, a top width of ’ with a depth of ’ is suitable, so answer B. Questions on open channel flow or vegetated waterways? Questions about anything in the whole presentation? Thanks
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