1. CE 515 Railroad Engineering
Drainage
Source: AREMA Ch. 5.1, 5.2
Iowa DOT Design Manual Chapter 4
J. Rose Lectures, Ch. 19
CE453 Drainage Lecture
“Transportation exists to conquer space and time -”

2. Video After Major Flooding!CO&E mainline west of Marion 3/18/2008
SVR Flood Damage Repairs (BH- HL)
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Source: J. Rose Lectures, Ch. 19

3. Drainage
The three most important element in good track are: #1 Drainage, #2 Drainage and #3 Drainage – Darrell Cantrell, Engineer Track (Retired) BNSF
Drainage:
Stormwater behavior related to the properties of Hydrology and Hydraulics.
Methods of analysis vary from location to location
The engineer has to maintain existing drainage patterns and not increase headwaters upstream or downstream.
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4. Hydrology
Hydrology: The study of rainfall events (inches or inches/hour) and runoff (cubic feet per second) as related to the engineering design of conveyance features such as ditches and culverts.
Design with Risk: Because of Cost and Feasibility  efficiency
Example:
Conveyance Feature Design Frequency
Culverts yr
Ditches yr
Storm Sewer yr
Storm Return Period
100 -year storm  1% probability occurs any given year
50 -year storm  2% probability occurs any given year
10 -year storm  10% probability occurs any given year
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5. Hydrology
Don’t forget to check the system with the 100-year storm after your design!
Equations and Programs:
Rational Formula (hydrology) peak discharge
Nation Resource Conservation (NRCS) TR 55 hydrograph
United States Geological Survey (USGS) Regression Equations peak discharge
NRCS TR 20 peak discharge and continuous simulation
US Army Corps of Engineers HECRAS continuous simulation
Peak Discharge Method for up to 200 Acres in Area
Rational Formula
Peak Discharge and Hydrograph Method for Areas Between 200 and 2000 Acres
NRCS Method
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6. Rational Formula Source: Iowa DOT Design Manual 4A-4
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Source: Iowa DOT Design Manual 4A-4

7. Rational Formula Runoff Coefficient (C)
Coefficient that represents the fraction of rainfall that becomes runoff
Depends on type of surface, character of the soil, Shape of the drainage area, Slope of the watershed, amount and type of surface storage, land use, duration of rainfall, intensity of rainfall etc.
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8. Rational Formula Runoff Coefficient (C) for rural area
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Source: Iowa DOT Design Manual 4A-4

9. Runoff coefficient vs. intensity for varying imperviousness.
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Picture
Source: Iowa DOT Design Manual 4A-4

10. Rational Formula
When the drainage area has several different parts with different C value.
Use the weighted average
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11. Rational Formula Drainage Area (A)
For DOT method measured in acres (hectares)
Combined area of all surfaces that drain to a given intake or culvert inlet
Determine boundaries of area that drain to same location
like Natural or human-made barriers
Determine the correct area:
Topographic maps
Aerial photos
Drainage maps
Field reviews
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Drainage Map.

12. Rational Formula Rainfall Intensity, (I)
The average rainfall intensity that is expected to fall on a drainage area over the duration of a storm.
Based on “design” event (i.e. 50-year storm)
Overdesign is costly
Underdesign may be inadequate
Based on value T and Tc
T = the recurrence interval or design frequency, measured in years.
Tc = the storm duration, measured in minutes
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13. Rational Formula Time of Concentration, Tc
Time for water to flow from hydraulically most distant point on the watershed to the point of reference downstream (the intake or culvert)
Rational method assumes peak run-off rate occurs when rainfall intensity (I) lasts (duration) >= TC
Used as storm duration
Iowa DOT says don’t use TC<5 minutes
Depends on: Size and shape of drainage area, type of surface, slope of drainage area, rainfall intensity
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14. Rational Formula Determining Tc and “I”
There are a lot of equations and charts could be used for Determining Tc and “I” . Iowa DOT provides the method below:
kinematic wave equation (trial and error)
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15. Rational Formula Determining Tc and “I” Nomograph
Trial and error method:
Known: surface, size (length), slope
Look up “n”
Estimate I (intensity)
Determine Tc
Check I and Tc against values in Table 5 (Iowa DOT, Chapter 4)
Repeat until Tc (table) ~ Tc (nomograph)
Peak storm event occurs when duration at least = Tc
Finally, after calculate C, I and A
Q= CIA
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Source: Iowa DOT Design Manual 4A-4

16. Hydraulics
Hydraulics: The study of water conveyance either through a conduit under pressure or a conduit exposed to atmospheric pressure.
Open Channel Hydraulics
Culvert Hydraulics
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Picture

17. Open Channel Hydraulics
The well-known Manning’s Euqation
V = R2/3*S1/2 (metric) V = 1.49 R2/3*S1/2 (English)
n n
where:
V = mean velocity (m/sec or ft/sec)
R = hydraulic radius (m, ft) = area of the cross section of flow (m2, ft2) divided by wetted perimeter (m,ft)
S = slope of channel
n = Manning’s roughness coefficient
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18. Open Channel Hydraulics
Manning’s roughness coefficient
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Source: Iowa DOT Design Manual 4A-4

19. Open Channel Hydraulics
Design:
Q= VA, V = 1.49 R2/3*S1/2 n Or
Using Charts developed by FHWA to solve Manning’s equation
for different cross sections.
FHWA Hydraulic Design Charts
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20. Open Channel Hydraulics
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21. Culvert Hydraulics
Inlet control and outlet control: what produces the highest headwater condition.
Culvert Design Steps:
Obtain site data
Railroad way cross section at culvert location
Establish inlet/outlet elevations, length, and slope of culvert
Determine allowable headwater depth (and probable tail water depth)
during design flood
control on design size – f(topography and nearby land use)
Select type and size of culvert
Examine need for energy dissipaters
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22. Culvert Hydraulics Source: J. Rose Lectures, Ch. 19
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Source: J. Rose Lectures, Ch. 19

23. Culvert Hydraulics Inlet Control
Flow is controlled by headwater depth and inlet geometry
Usually occurs when slope of culvert is steep and outlet is not submerged
Supercritical, high v, low d
Most typical
Following methods ignore velocity head
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Source: CE453 Drainage Lecture

24. Culvert Hydraulics
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25. Culvert Hydraulics Outlet Control
When flow is governed by combination of headwater depth, entrance geometry, tailwater elevation, and slope, roughness, and length of culvert
Subcritical flow
Frequently occur on flat slopes
Concept is to find the required HW depth to sustain Q flow
Tail water depth often not known (need a model), so may not be able to estimate for outlet control conditions
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Source: CE453 Drainage Lecture

26. Culvert Hydraulics Source: CE453 Drainage Lecture
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Source: CE453 Drainage Lecture

27. Culvert Hydraulics
Afte
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28. Questions?
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