CTC 440 Review n Determining peak flows n
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CTC 440 Review n Determining peak flows n n Rational method Q=CIA Intensity determined from IDF curves Set time of concentration=storm duration 1
CTC 440 Sizing Structures n Hydraulic Devices n n n Pipes Culverts Inlets Ditch &/or gutter flow Storm drainage systems Detention structures 2
Subjects n Open Channel Flow n n n Ditch flow Gutter flow Pipe flow (non-pressurized) 3
Objectives n n Know how to use Manning’s equation for uniform flow calculations Know how to calculate Normal Depth 4
Open Channel Flow n Open to the atmosphere n n Uniform flow-EGL/HGL/Channel Slope are parallel n n Creek/ditch/gutter/pipe flow velocity/depth constant Varied flow-EGL/HGL/Channel Slope not parallel n velocity/depth not constant 5
Uniform Flow in Open Channels n n n Water depth, flow area, Q and V distribution at all sections throughout the entire channel reach remains unchanged The EGL, HGL and channel bottom lines are parallel to each other No acceleration or deceleration 6
Manning’s Equation n n Irish Engineer On the Flow of Water in Open Channels and Pipes Empirical equation See more: n n http: //manning. sdsu. edu/ http: //el. erdc. usace. army. mil/elpubs/pdf/sr 10. pdf #search=%22 manning%20 irish%20 engineer%22 7
Manning’s Equation-Metric Q=AV=(1/n)(A)(Rh)2/3 S 1/2 Where: Q=flow rate (cms) A=wetted cross-sectional area (m 2) Rh=Hydraulic Radius=A/WP (m) WP=Wetter Perimeter (m) S=slope (m/m) n=friction coefficient (dimensionless) 8
Manning’s Equation-English Q=AV=(1. 486/n)(A)(Rh)2/3 S 1/2 Where: Q=flow rate (cfs) A=wetted cross-sectional area (ft 2) Rh=Hydraulic Radius=A/WP (ft) WP=Wetted Perimeter (ft) S=slope (ft/ft) n=friction coefficient (dimensionless) 9
Manning’s Friction Coefficient http: //www. lmnoeng. com/manningn. h tm Typical values: n n Concrete pipe: n=. 013 CMP pipe: n=. 024 10
Area and Hydraulic Radius n A-wetted area WP-wetted perimeter n Rh=A/WP n 11
Triangular/Trapezoidal Channels n Must use trigonometry to determine area and wetted perimeters 12
Pipe Flow n n Hydraulic radii and wetted perimeters are easy to calculate if the pipe is flowing full or half-full If pipe flow is at some other depth, then tables, figures, or software (flowmaster) are usually used 13
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Example-Find Q Find the discharge of a rectangular channel 5’ wide w/ a 5% grade, flowing 1’ deep. The channel has a stone and weed bank (n=. 035). A=5 sf; WP=7’; Rh=0. 714 ft S=. 05 Q=38 cfs 15
Example-Find S A 3 -m wide rectangular irrigation channel carries a discharge of 25. 3 cms @ a uniform depth of 1. 2 m. Determine the slope of the channel if Manning’s n=. 022 A=3. 6 sm; WP=5. 4 m; Rh=0. 667 m S=. 041=4. 1% 16
Using Manning’s equation to estimate pipe size (Diameter) n n n n Size pipe for Q=39 cfs Assume full flow Assume concrete pipe on a 2% grade Put Rh and A in terms of Dia. Solve for D=2. 15 ft = 25. 8” Choose a 27” or 30” RCP Velocity is approx. 9. 8 ft/sec 17
Using Manning’s equation to estimate pipe size n n n n Size pipe for Q=220 cfs Assume full flow Assume concrete pipe on a 2% grade Put Rh and A in terms of Dia. Solve for D=4. 1 ft = 49. 5” Choose a 54” RCP Velocity is approx. 13. 8 ft/sec ===high What can we do if velocities are high? 18
Solving for Normal Depth n n Given Q, the depth at which the water flows uniformly Use Manning’s equation n Must solve by trial/error (depth is in area term and in hydraulic radius term) 19
Normal Depth Example n n Find normal depth in a 10. 0 -ft wide concrete rectangular channel having a slope of 0. 015 ft/ft and carrying a flow of 400 cfs. Assume: n N=0. 013 20
Normal Depth Example 7 -3 Assumed D Area (ft) (sqft) Peri. (ft) Rh Rh^. 66 Q (cfs) (ft) 2. 00 20 14 1. 43 1. 27 356 3. 00 30 16 1. 88 1. 52 640 2. 15 21. 5 14. 3 1. 50 1. 31 396 21
Inlets n Curb-opening inlet n n Gutter Inlet n n n No grate (not hydraulically efficient; rarely used) Grate only-used if no curb (common if no curb) Slotted (rarely used) Combination Inlet n Used w/ curbs (common for curbed areas) 22
Inlets n Capacity usually estimated using orifice or weir equations 23
Grates n n n Reticuline Rectangular Parallel bar 24
Froude Number n n n F=Vel/(g*D). 5 F=Froude # V=Velocity (fps or m/sec) D=hydraulic depth=a/T (ft or m) g=gravitational constant n n n F=1 (critical flow) F<1 (subcritical; tranquil flow) F>1 (supercritical; rapid flow) 25
History n Water Quality Act-1987 n n First regulations dealing with discharge of stormwater Phase I Stormwater Regulations-1990 n n NYSDEC is local permitting authority NYSDEC issued 2 general permits-1993 n n n Industrial Site Runoff Construction Projects > 5 acres (Phase I) Phase II Stormwater Regulations-1999 n Apply to Construction Projects > 1 acre 26
Stormwater Definitions n n n SWPPP-Stormwater Pollution Prevention Plan NPDES-National Pollutant Discharge Elimination System SPDES-State Pollutant Discharge Elimination System MS 4 -Municipal Separate Storm Sewer System NOI-Notice of Intent Blue Book-”New York Standards and Specification for Erosion and Sediment Control” 27
SWPPP-Contents n n n n Standards for Construction Activities Background project info Site Map Soil Description Construction Phasing Plan Pollution Prevention Measures Description of Construction and Waste Materials Temporary and Permanent Structural and Vegetative Measures 28
SWPPP-Contents (contents) n n n n Map showing control measures Details of control measures Identify temporary measures to be converted to permanent control measures Maintenance Schedule Name of receiving water Description of structural practices used to divert flows Description of existing data that describes the stormwater runoff characteristics at the site 29
Commonly Used SWPPP Measures n n n n Construction Entrance Mulching/Seeding Silt Fences Straw Bale Dikes Drop Inlet Protection Stone Check Dams Prefabricated Check Dams 30
Construction Entrance http: //pasture. ecn. purdue. edu/~sedspec/images/construction. jpg http: //www. harfordcountymd. gov/dpw/eng&const/Water. Resources/Images/Sedimentcont 2. jpg 31
Erosion Control (Mulching/Seeding) http: //www. terra-mulch. com/photos/11 -11. JPG http: //www. ssseeds. com/ecb/photos/WS 05/images/WS 05%202 -1%20 Over%20 Mulch. jpg 32
Silt fences www. acfenvironmental. com/bmp_siltfence. htm www. forestry. state. ar. us/bmp/appn_soil. html 33
Straw Bale Dikes http: //www. salmonhabitat. org/images/v 3 f 52 b. gif http: //www. forester. net/images/ec_0103_p 78_top. jpg 34
Drop Inlet Protection http: //unix. eng. ua. edu/~rpitt/Class/Erosioncontrol/Module 8_files/image 050. gif http: //www. greatamericantec. com/images/inlet. jpg 35
Stone Check Dams http: //www. ncc-swnpdes. com/images/stone_creek_dam. jpg http: //www. dfr. state. nc. us/images/wq/glossary/rockcheckdam. jpg 36
Other Check Dams http: //www. lakemac. infohunt. nsw. gov. au/erosion/images/09051. gif http: //www. wsdot. wa. gov/NR/rdonlyres/BA 478915 -1 B 80 -4188 -BB 59 -37358244 CBDF/0/Check. Dam_Jan 05. jpg 37
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Detention Structures n Designed for water quality, attenuation of peak flows, infiltration, aesthetics 39
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Review Questions n n n n What is Manning’s equation (english)? What else is Manning’s equation called? What is the hydraulic radius? What does SWPPP stand for? Manning’s equation is used to solve for? What are units of the hydraulic radius? What does “open” mean 41
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