CTC 440 Review

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CTC 440 Review

• Determining peak flows
• Rational method
• QCIA
• Intensity determined from IDF curves
• Set time of concentrationstorm 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 Mannings 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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Mannings 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
  search22manning20irish20engineer22

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Mannings Equation-Metric

• QAV(1/n)(A)(Rh)2/3S1/2
• Where
• Qflow rate (cms)
• Awetted cross-sectional area (m2)
• RhHydraulic RadiusA/WP (m)
• WPWetter Perimeter (m)
• Sslope (m/m)
• nfriction coefficient (dimensionless)

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Mannings Equation-English

• QAV(1.486/n)(A)(Rh)2/3S1/2
• Where
• Qflow rate (cfs)
• Awetted cross-sectional area (ft2)
• RhHydraulic RadiusA/WP (ft)
• WPWetter Perimeter (ft)
• Sslope (ft/ft)
• nfriction coefficient (dimensionless)

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Mannings 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).
• A5 sf WP7 Rh0.714 ft
• S.05
• Q38 cfs

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Example-Find S

• A 3-m wide rectangular irrigation channel
  carries a discharge of 25.3 cms _at_ a uniform depth
  of 1.2m. Determine the slope of the channel if
  Mannings n.022
• A3.6 sm WP5.4m Rh0.667m
• S.0414.1

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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 Mannings equation to estimate pipe size

• Size pipe for Q39 cfs
• Assume full flow
• Assume concrete pipe on a 2 grade
• Put Rh and A in terms of Dia.
• Solve for D2.15 ft 25.8
• Choose a 27 or 30 RCP
• Velocity is approx. 9.8 ft/sec

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Using Mannings equation to estimate pipe size

• Size pipe for Q220 cfs
• Assume full flow
• Assume concrete pipe on a 2 grade
• Put Rh and A in terms of Dia.
• Solve for D4.1 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 Mannings 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
• N0.013

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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
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Inlets

• Capacity usually estimated using orifice or weir
  equations

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Froude Number

• FVel/(gD).5
• FFroude
• VVelocity (fps or m/sec)
• Dhydraulic deptha/T (ft or m)
• ggravitational constant
• F1 (critical flow)
• Flt1 (subcritical tranquil flow)
• Fgt1 (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 gt 5 acres (Phase I)
• Phase II Stormwater Regulations-1999
• Apply to Construction Projects gt 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//pasture.ecn.purdue.edu/sedspec/sedspec/ima
ges/construction.jpg
http//www.harfordcountymd.gov/dpw/engconst/Water
Resources/Images/Sedimentcont2.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
202-120Over20Mulch.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.
jpg
http//www.dfr.state.nc.us/images/wq/glossary/rock
checkdam.jpg
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Other Check Dams
http//www.lakemac.infohunt.nsw.gov.au/erosion/ima
ges/09051.gif
http//www.wsdot.wa.gov/NR/rdonlyres/BA478915-1B80
-4188-BB59-37358244CBDF/0/CheckDam_Jan05.jpg
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Detention Structures

• Designed for water quality, attenuation of peak
  flows, infiltration, aesthetics

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