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.
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CE 515 Railroad Engineering
DrainageSource: AREMA Ch. 5.1, 5.2
Iowa DOT Design Manual Chapter 4J. Rose Lectures, Ch. 19CE453 Drainage Lecture
“Transportation exists to conquer space and time -”
Video
After Major Flooding!CO&E mainline west of Marion 3/18/2008
http://www.youtube.com/watch?v=aSkrznCxfOo
SVR Flood Damage Repairs (BH- HL)
http://www.youtube.com/watch?v=YbbKPoPvUuo
Source: J. Rose Lectures, Ch. 19
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.
HydrologyHydrology: 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 50 yr Ditches 50 yr Storm Sewer 50 yr
Storm Return Period100 -year storm 1% probability occurs any given year50 -year storm 2% probability occurs any given year10 -year storm 10% probability occurs any given year
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 AreaRational Formula
Peak Discharge and Hydrograph Method for Areas Between 200 and 2000 AcresNRCS Method
Rational FormulaRunoff 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.
Runoff coefficient vs. intensity for varying imperviousness.
Source: Iowa DOT Design Manual 4A-4
Picture http://hurkunderground.com/Railroad%20Drainage.ppt.
Rational Formula
When the drainage area has several different parts with different C value.
Use the weighted average
Rational FormulaDrainage 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
Drainage Map. www.croppro.ca/maps/drainage.html
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 costlyUnderdesign 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
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
Rational FormulaDetermining 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)
Rational FormulaDetermining 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 AQ= CIA
Source: Iowa DOT Design Manual 4A-4
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
Picture http://hurkunderground.com/Railroad%20Drainage.ppt.
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 channeln = Manning’s roughness coefficient
Open Channel Hydraulics
Design:
Q= VA, V = 1.49 R2/3*S1/2
nOr
Using Charts developed by FHWA to solve Manning’s equation for different cross sections.
FHWA Hydraulic Design Chartshttp://www.ctre.iastate.edu/educweb/ce453/FHWA%20Hydraulic%20Design.pdf
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
Culvert HydraulicsInlet 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
Source: CE453 Drainage Lecture
Culvert HydraulicsOutlet 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
Source: CE453 Drainage Lecture
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