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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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