CE 453 Lab #10Page 1 of 7

DRAINAGE DESIGN

PROBLEM:

At this point in the design of a section of roadway it is necessary to establish the existing and future drainage needs and take steps to design the required drainage structures. Existing drainage patterns prior to the construction must be identified and maintained after the construction. The addition of the pavement surface and associated grades will contribute additional runoff and will require consideration. To complete this phase of the project, the design team must identify drainage areas, select one of these areas for design, compute the size of a drainage structure and determine its station on the plan and profile.

COMPLETION STEPS:

  1. Define one drainage area (watershed area) for your facility. Starting in Microstation load your horizontal alignment, making sure that you have the TIN loaded as well. Go to the first portion of the alignment and define the area from 107+00 to 111+00. The green lines that cross the alignment represent the existing drainage ways. Select one of these drainage ways and determine its approximate station (use the Microstation measurement tool). Open ArcView, using the files you used in the location study lab at the beginning of the semester. Make a new layer and outline the approximate boundary of your drainage basin (use the polygon drawing tool on the new layer that you created – be SURE to draw the basins as polygons. Draw separate polygons on each side of the road). Pay attention to how the typical section drains, because of the DOT policy regarding median drainage.
  1. Now draw a new layer for this drainage basin, as it will exist after you put in your new road. Include the half of the roadway that contributes to the drainage area, and the drainage basin in the median. Note culvert locations on the map and identify the direction of flow of water through the culvert (left to right or right to left) at this point. You may need to look at your cross-section nearest to this point (on your drawing XS.dgn). Pay attention to how existing drainage will be handled at the connections of the new route to existing routes along the alignment. Note any need for special ditches on the profile as to location, direction of flow and grade of ditch bottom. Another point to remember is that DOT policy is to drain the median to the high side of the roadway.
  1. In ArcView, calculate the geometric area of the drainage section (double click with the pointer arrow – change map options to display in desired units, e.g., hectares). Also identify the character of the terrain (hilly, flat, rolling etc.). Use the Iowa DOT rational method to determine quantity of water for areas less than 4 hectares or the Iowa Runoff Chart for areas up to 400 hectares. You may need to convert between the English and metric systems. If you do, be sure to carry one more significant figure (than you need) throughout your calculations.
  1. Design one culvert at the location where water would likely cross the roadway. Use information from the class lecture on drainage to design the culvert. Your memorandum must document the amount of cover provided. Design culverts such that water stays at least 0.6 m. below the top of the pavement for the design storm. (This keeps the water out of the base material)
  1. The design discharge at each location should be obtained using the area computed in step 4 and the Iowa chart relating peak rate of runoff to drainage area, land use and frequency factor (assume FF = 50 years). Each culvert design selected should be checked to provide inlet control. Use a box culvert.
  1. For your drainage cross-section you will use the roadway cross-section closest to the actual location selected. Make a copy of your file XS.dgn and delete all the sections you are not using. Your drawing should include the roadway section with profile elevation of the road surface at centerline, station of the structure, skew angle (note on a separate sketch near the cross section), inlet and outlet flow line elevations of the structure, length of structure, slope of the foreslopes, and the slope of the drainage structure. The section should be positioned in such a manner that the viewer is looking from the lower route station to the next higher station in the establishment of left and right elevations. This will put the north side of the roadway on the left. Note: you do not have to design the ditch (you can assume it is parallel with the road) but you should realize that you may need more culverts.
  1. Identify the structure by station, size (opening diameter and length), material type, and flow line elevations left and right, and skew where necessary.

view from the South

view from the West

Theseare 3D representations of your study area to help you visualize the drainage basins.

GRADING CONSIDERATIONS AND EXPECTED RESULTS:

15%Drainage memorandum covering your design parameters, assumptions, and recommendations – discuss what you did and include the following items:

15%Map showing drainage areas before construction. Show arrows depicting flow direction

15%Area determination and flow for the drainage basin

20% Description and calculations (either rational method or Iowa Runoff chart)

10%Location (centerline station and plan map showing SIMPLE sketch of structure) and specifications for structure required (transverse and longitudinal)

Specs include:

a)Flowline Elevations

b)Skew

c)Pipe Size

d)Pipe Length

e)Slope

f)Discharge (flow) at each structure

Include any referenced tables or graphs and calculations used in the solution (in your Appendix).

10%Cross section at the structure identifying:

g)The road profile elevation

h)Foreslopes

i)Flow line elevation at the centerline of roadway

j)Inlet and outlet elevations

k)Pipe diameter or dimensions of box culvert

l)Length of pipe and aprons

m)Skew angle if appropriate

15%Appendix with Calculations - Neat and Easy to Follow. Use inlet control nomographs for culvert design.

You may use the handouts provided in class and materials from the DOT Office of Design Web Page.

Your grade may be reduced by up to 30% for grammatical errors or faulty presentation.

Background information for the use of the Iowa Runoff Chart:

In the 1950's, the Iowa State Highway Commission (now Iowa DOT) adapted Bureau of Public Roads' Chart 1021.1, "Highway Drainage Manual", 1950. (The BPR chart was adapted from original work performed by W.D. Potter, "Surface Runoff from Small Agricultural Watersheds," Research Report No. 1 I-B, (Illinois) Highway Research Board, 1950.) The Iowa Runoff Chart has been widely used by the Iowa DOT and counties since then.

The chart is self-explanatory. However, its use does require the exercise of judgment in selecting the land use and land slope factors. It can be used for rural watersheds draining up to 1000 acres.

The following is intended to aid in that judgment:

Very HillyLand --- is best typified by the bluffs bordering the Mississippi and the MissouriRivers. This terrain is practically mountainous (for Iowa) in character. Small areas of very hilly land can be found in all parts of the state. Typically, they can be found near the edge of the flood plains of the major rivers.

HillyLand --- is best typified by the rolling hills of south central Iowa. Interstate 35 in Clarke and WarrenCounties traverses many hilly watersheds. Small areas of hilly land can be found in all parts of the state.

Rolling Land --- is best typified by the more gently rolling farm lands of central Iowa. Interstate 80 in Cass and AdairCounties traverses many watersheds with rolling topography. Small areas of rolling land can be found in all parts of the state.

Flat land --- is best typified by the farm lands of the north central part of the state. U.S. 69 traverses many flat watersheds in Hamilton and WrightCounties. Small areas of flat land can be found in all areas of the state.

Very FlatLand --- is best typified by the Missouri River flood plain. Interstate 29 is located on this type of land for most of its length. Much of Dickinson, Emmet, Kossuth, Winnebago, and Palo AltoCounties are also in this classification. Small areas of very flat land can be found in all parts of the state.

The peak discharge rate, Q, taken from the Iowa Chart for a particular watershed will have a frequency of 50 years, or a two per cent chance of occurring in any one year. This is the recurrence interval used at the Iowa DOT for primary and secondary highways. Frequency factors for other recurrence intervals are obtained from the chart. A frequency factor of 1.2 has been used in Iowa for a recurrence interval of 100 years.

Use this chart only for rural watersheds and the limitations of drainage areas listed below. The equations were developed by finding the best statistical fit to the curve on the Runoff Chart. At the larger drainage areas (600 to 1000 acres), the equation overestimates Q taken from the chart by up to 7%. In most cases, however, this would not result in a larger culvert size. If the designer questions the equation results, use the curve on the Chart. Be aware that error (overestimating or underestimating) may also result from interpolating the Q from the curve.

English equation: (For drainage areas, 2 < A < 1000 acres)

Qdesign= LF x FF x Q

where: Q = 8.124 A0.739 ; Q is in ft3/sec , A is in acres

Metric equation: (For drainage areas, 1 < A < 400 hectares)

Qdesign= LF x FF x Q

where: Q = 0.446 A0.740 ; Q is in m3/sec , A is in hectares

Frequency Factor (FF)

Land Use and Slope Description (LF)