EXAM 2 REVIEW

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EXAM 2 REVIEW
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• 1. Drainage problem (25 pts)
• Below you see a cross-section of a ditch. It
  runs parallel to a 200-acre field consisting of
  permanent pasture and rolling terrain. Assume
  that all of the runoff goes to the ditch. The
  slope of the ditch is .02 feet per foot and the
  Mannings number is .03. Use a trapezoidal
  channel with a five foot base and a 2H1V side
  slope and the attached Iowa Runoff Chart.
  Assume you need 2 feet of freeboard (vertical) in
  the ditch to avoid inundating the base material.
  Show your solution lines on the graphs.
• How deep should you design the ditch if the
  design storm is a 25 year flood?

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• Qdesign Q FF LF
• Qdesign 430 0.4 0.8 137.6

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• Therefore the flow depth is about 1.8 feet.
• Adding two feet of freeboard gives us a total
  depth of about 3.8 feet.
• The velocity is about 9 fps, so unless the
  channel is paved erosion is likely to be a
  problem.

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• 2. Vertical and Horizontal Alignment problem (25
  pts)
• A two-lane rural road (12-foot paved lanes, 2
  normal crown section, ignore shoulder) has a
  design speed of 60 mph and a maximum (full)
  superelevation rate of 6 percent. There is a
  horizontal curve in the road in the vicinity of a
  vertical curve. Assume a spiral curve is used to
  attain superelevation. What is the elevation of
  the outside edge of the pavement at the station
  half way along the spiral?
• Station SC (spiral to curve) Station VPI
• VPI elevation 700.00 feet
• g1 2 g2 -3

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• Remembering that the normal crown is taken out in
  the tangent runoff, we know that the cross-slope
  transitions from 0 to full super uniformly in
  the spiral.

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• Using the maximum slope ratio from the table we
  calculate the length of the spiral
• ls 6 12 222 159.84 say 160

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• We now calculate the parameters for the vertical
  curve
• A g2 g1 -3 2 -5
• L KA 151 5 755 (say 760)
• r A/100L 0.0000658
• e AL/800 4.75

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• Assume a station for the VPI of 10000 ( sta SC)
• Elev VPC elev VPI 0.02 (L/2)
• 700 7.6 692.40
• Sta VPC 10000 380 9620

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• Elev VPI (curve) 700- e 695.25
• Sta x sta SC - ls/2
• 10000 80 9920

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• 4. Answer the following questions (each is worth
  3 points).
• Discuss the tradeoffs (safety, cost, or whatever)
  between flat 61 and maximum 41 median cross
  slope.
• ROW greater for 61, so cost is higher
• 61 is safer than 41

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• 4. Answer the following questions (each is worth
  3 points).
• Name the three median types.
• Depressed, flush, raised
• In general, slopes above what ratio require a
  barrier?
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• Describe the traffic conditions that you would
  expect at a Level-of-Service F.
• Break down, no ability to maneuver, high
  workload

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• The coefficient C in the Rational Method
  equation to calculate discharge represents what
  ratio?
• Runoff/rainfall
• Which is a better way to deal with an object in
  the clear zone, removal or a guardrail? Why?
• Removal. Guardrail is an obstacle.
• The I in the Rational Method equation is a
  function of what two factors?
• Sag and crest vertical curves have maximum
  lengths for drainage function. Is this more
  likely to be true in rural or urban areas? Why?

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• The I in the Rational Method equation is a
  function of what two factors?
• Time of concentration and return period
• Sag and crest vertical curves have maximum
  lengths for drainage function. Is this more
  likely to be true in rural or urban areas? Why?
• Urban. In rural areas cross-slope carries the
  water off the pavement, curbs in urban areas
  prevent this.

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• Name three of the five possible actions to deal
  with an object in the clear zone.
• Remove, relocate, reduce severity, redirect,
  delineate

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• At what level of service would you expect to see
  breakdown?
• F

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• There are at least four characteristics that
  should be considered in the design (i.e., sizing,
  shape, etc.) of a drainage channel (for example -
  ease of maintenance). Name three others.
• Capacity, minimum hazard to traffic, hydraulic
  efficiency

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• C is a function of several factors and/or
  surface characteristics. Name two.
• slope, material.