1 ctc 440 review determining peak flows rational method q=cia intensity determined from idf curves...
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CTC 440 Review
Determining peak flows Rational method Q=CIA Intensity determined from IDF curves Set time of concentration=storm
duration
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CTC 440 Sizing Structures
Hydraulic Devices Pipes Culverts Inlets Ditch &/or gutter flow Storm drainage systems Detention structures
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Subjects
Open Channel Flow Ditch flow Gutter flow Pipe flow (non-pressurized)
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Objectives
Know how to use Manning’s equation for uniform flow calculations
Know how to calculate Normal Depth
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Open Channel Flow Open to the atmosphere
Creek/ditch/gutter/pipe flow Uniform flow-EGL/HGL/Channel
Slope are parallel velocity/depth constant
Varied flow-EGL/HGL/Channel Slope not parallel velocity/depth not constant
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Uniform Flow in Open Channels
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
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Manning’s Equation Irish Engineer On the Flow of Water in Open Channels
and Pipes Empirical equation See more:
http://manning.sdsu.edu/\ http://el.erdc.usace.army.mil/elpubs/pdf/
sr10.pdf#search=%22manning%20irish%20engineer%22
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Manning’s Equation-Metric
Q=AV=(1/n)(A)(Rh)2/3S1/2
Where:Q=flow rate (cms)A=wetted cross-sectional area (m2)Rh=Hydraulic Radius=A/WP (m)
WP=Wetter Perimeter (m)S=slope (m/m)n=friction coefficient (dimensionless)
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Manning’s Equation-English
Q=AV=(1.486/n)(A)(Rh)2/3S1/2
Where:Q=flow rate (cfs)A=wetted cross-sectional area (ft2)Rh=Hydraulic Radius=A/WP (ft)
WP=Wetter Perimeter (ft)S=slope (ft/ft)n=friction coefficient (dimensionless)
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Manning’s Friction Coefficient
http://www.lmnoeng.com/manningn.htm
Typical values: Concrete pipe: n=.013 CMP pipe: n=.024
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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=.05Q=38 cfs
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Example-Find S
A 3-m wide rectangular irrigation channel carries a discharge of 25.3 cms @ a uniform depth of 1.2m. Determine the slope of the channel if Manning’s n=.022
A=3.6 sm; WP=5.4m; Rh=0.667m
S=.041=4.1%
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Triangular/Trapezoidal Channels
Must use trigonometry to determine area and wetted perimeters
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Pipe Flow
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
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Using Manning’s equation to estimate pipe size 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
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Using Manning’s equation to estimate pipe size 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
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Normal Depth
Given Q, the depth at which the water flows uniformly
Use Manning’s equation Must solve by trial/error (depth is in
area term and in hydraulic radius term)
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Normal Depth Example
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=0.013
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Normal Depth Example 7-3
Assumed D (ft)
Area (sqft)
Peri. (ft)
Rh (ft)
Rh^.66 Q (cfs)
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
Inlets
Capacity usually estimated using orifice or weir equations
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Froude Number F=Vel/(g*D).5
F=Froude # V=Velocity (fps or m/sec) D=hydraulic depth=a/T (ft or m) g=gravitational constant
F=1 (critical flow) F<1 (subcritical; tranquil flow) F>1 (supercritical; rapid flow)
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Stormwater Definitions SWPPP-Stormwater Pollution Prevention Plan NPDES-National Pollutant Discharge
Elimination System SPDES-State Pollutant Discharge Elimination
System MS4-Municipal Separate Storm Sewer System NOI-Notice of Intent Blue Book-”New York Standards and
Specification for Erosion and Sediment Control”
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History Water Quality Act-1987
First regulations dealing with discharge of stormwater
Phase I Stormwater Regulations-1990 NYSDEC is local permitting authority NYSDEC issued 2 general permits-1993
Industrial Site Runoff Construction Projects > 5 acres (Phase I)
Phase II Stormwater Regulations-1999 Apply to Construction Projects > 1 acre
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SWPPP-Contents 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
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SWPPP-Contents (contents) 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
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Commonly Used SWPPP Measures
Construction Entrance Mulching/Seeding Silt Fences Straw Bale Dikes Drop Inlet Protection Stone Check Dams Prefabricated Check Dams
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Construction Entrance
http://www.harfordcountymd.gov/dpw/eng&const/WaterResources/Images/Sedimentcont2.jpg
http://pasture.ecn.purdue.edu/~sedspec/sedspec/images/construction.jpg
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Erosion Control (Mulching/Seeding)
http://www.terra-mulch.com/photos/11-11.JPG
http://www.ssseeds.com/ecb/photos/WS05/images/WS05%202-1%20Over%20Mulch.jpg
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Silt fences
www.acfenvironmental.com/ bmp_siltfence.htm
www.forestry.state.ar.us/ bmp/appn_soil.html
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Straw Bale Dikes
http://www.salmonhabitat.org/images/v3f52b.gif
http://www.forester.net/images/ec_0103_p78_top.jpg
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Drop Inlet Protection
http://unix.eng.ua.edu/~rpitt/Class/Erosioncontrol/Module8/Module8_files/image050.gif
http://www.greatamericantec.com/images/inlet.jpg
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Stone Check Dams
http://www.ncc-swnpdes.com/images/stone_creek_dam.jpghttp://www.dfr.state.nc.us/images/wq/glossary/rockcheckdam.jpg
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Other Check Dams
http://www.wsdot.wa.gov/NR/rdonlyres/BA478915-1B80-4188-BB59-37358244CBDF/0/CheckDam_Jan05.jpg
http://www.lakemac.infohunt.nsw.gov.au/erosion/images/09051.gif
Detention Structures
Designed for water quality, attenuation of peak flows, infiltration, aesthetics
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