1. CTC 440 Review Determining peak flows Rational method Q=CIA
Intensity determined from IDF curves
Set time of concentration=storm duration

2. CTC 440 Sizing Structures Hydraulic Devices Pipes Culverts Inlets
Ditch &/or gutter flow
Storm drainage systems
Detention structures

3. Subjects Open Channel Flow Ditch flow Gutter flow
Pipe flow (non-pressurized)

4. Objectives
Know how to use Manning’s equation for uniform flow calculations
Know how to calculate Normal Depth

5. 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

6. 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

7. Manning’s Equation Irish Engineer
On the Flow of Water in Open Channels and Pipes
Empirical equation
See more:

8. 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)

9. 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)

10. Manning’s Friction Coefficient
Typical values:
Concrete pipe: n=.013
CMP pipe: n=.024

11. 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

12. Example-Find S
A 3-m wide rectangular irrigation channel carries a discharge of 25.3 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%

13. Triangular/Trapezoidal Channels
Must use trigonometry to determine area and wetted perimeters

14. 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

16. 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

17. 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 ft/sec ===high

18. 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)

19. Normal Depth Example
Find normal depth in a 10.0-ft wide concrete rectangular channel having a slope of ft/ft and carrying a flow of 400 cfs.
Assume:
N=0.013

20. Normal Depth Example 7-3 Assumed D (ft) Area (sqft) Peri. (ft) Rh (ft)
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

21. Inlets
Capacity usually estimated using orifice or weir equations

22. 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)

23. 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”

24. History Water Quality Act-1987 Phase I Stormwater Regulations-1990
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

25. 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

26. 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

27. Commonly Used SWPPP Measures
Construction Entrance
Mulching/Seeding
Silt Fences
Straw Bale Dikes
Drop Inlet Protection
Stone Check Dams
Prefabricated Check Dams

28. Construction Entrance

29. Erosion Control (Mulching/Seeding)

30. Silt fences www.acfenvironmental.com/ bmp_siltfence.htm
bmp/appn_soil.html

31. Straw Bale Dikes http://www.salmonhabitat.org/images/v3f52b.gif

32. Drop Inlet Protection

33. Stone Check Dams http://www.ncc-swnpdes.com/images/stone_creek_dam.jpg

34. Other Check Dams

35. Detention Structures
Designed for water quality, attenuation of peak flows, infiltration, aesthetics