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**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 -”

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**Video After Major Flooding!CO&E mainline west of Marion 3/18/2008**

SVR Flood Damage Repairs (BH- HL) Show example on board Source: J. Rose Lectures, Ch. 19

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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. Show example on board

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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 Show example on board

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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 Show example on board

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**Rational Formula Source: Iowa DOT Design Manual 4A-4**

Show example on board Source: Iowa DOT Design Manual 4A-4

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**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. Show example on board

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**Rational Formula Runoff Coefficient (C) for rural area**

Show example on board Source: Iowa DOT Design Manual 4A-4

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**Runoff coefficient vs. intensity for varying imperviousness.**

Show example on board Picture Source: Iowa DOT Design Manual 4A-4

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Rational Formula When the drainage area has several different parts with different C value. Use the weighted average Show example on board

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**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 Show example on board Drainage Map.

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**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 Show example on board

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**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 Show example on board

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**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) Show example on board

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**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 Show example on board Source: Iowa DOT Design Manual 4A-4

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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 Show example on board Picture

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**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 Show example on board

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**Open Channel Hydraulics**

Manning’s roughness coefficient Show example on board Source: Iowa DOT Design Manual 4A-4

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**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 Show example on board

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**Open Channel Hydraulics**

Show example on board

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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 Show example on board

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**Culvert Hydraulics Source: J. Rose Lectures, Ch. 19**

Show example on board Source: J. Rose Lectures, Ch. 19

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**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 Show example on board Source: CE453 Drainage Lecture

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Culvert Hydraulics Show example on board

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**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 Show example on board Source: CE453 Drainage Lecture

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**Culvert Hydraulics Source: CE453 Drainage Lecture**

Show example on board Source: CE453 Drainage Lecture

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Culvert Hydraulics Afte Show example on board

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Questions? Thank You

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