Culverts Design

Quiz Question

1.Another factor that significantly affects the performance of a culvert is its __________. The culvert inlet may consist of a culvert barrel projecting from the roadway fill or mitered to the embankment slope. Other inlets have headwalls, wingwalls, and apron slabs or standard end sections of concrete or metal.
Inlet configuration
2. The design of a culvert includes a determination of the following:

  • Impacts of various culvert sizes and dimensions on upstream and downstream flood risks, including the implications of embankment overtopping.
  • How will the proposed culvert/embankment fit into the relevant major drainageway master plan, and are there multipurpose objectives that should be satisfied?
  • Alignment, grade, and length of culvert.
  • Size, type, end treatment, headwater, and outlet velocity.
  • Amount and type of cover.
  • Public safety issues, including the key question of whether or not to include a safety/debris rack (Photograph CU-4).
  • Pipe material.
  • Type of coating (if required).
  • Need for fish passage measures, in specialized cases.
  • Need for protective measures against abrasion and corrosion.
  • Need for specially designed inlets or outlets.
  • Structural and geotechnical considerations, which are beyond the scope of this chapter.
3.The discharge used in culvert design is usually estimated on the basis of a preselected storm recurrence interval, and the culvert is designed to operate within acceptable limits of risk at that flow rate. The design recurrence interval should be based on the criteria set forth in the :
POLICY chapter of this Manual. Specifically, refer to Tables DP-1 through DP-3 for street overtopping criteria.
Yearly rain predictions
4.In selecting the design headwater elevation, the designer should consider which one of the followings:

  1. Anticipated upstream and downstream flood risks, for a range of return frequency events.
  2. Damage to the culvert and the roadway.
  3. Traffic interruption.
  4. Hazard to human life and safety.
  5. Headwater/Culvert Depth (HW/D) ratio.
  6. Low point in the roadway grade line.
  7. Roadway elevation above the structure.
  8. Elevation at which water will flow to the next cross drainage
  9. Relationship to stability of embankment that culvert passes through.
1,2,4 and 5
1, 3, 5, 7
1 through 9
5.Tailwater is the flow depth in the downstream channel measured from the invert at the culvert outlet. It can be an important factor in culvert hydraulic design because a submerged outlet may cause the culvert to flow full rather than partially full.
6.A field inspection of the downstream channel should be made to determine:
whether there are obstructions that will influence the tailwater depth.
If the channel is deep enough
7.Which one of the followings at the entrance of a culverts controls the flow capacity of the culvert?
Depth of headwater
Cross-sectional area
Inlet edge configuration
Barrel shape
All of the above
8. When a culvert operates under inlet control, headwater depth and the inlet edge configuration determine the culvert capacity with the culvert barrel usually flowing only partially full.
9.For a culvert operating with inlet control, the roughness, slope, and length of the culvert barrel and outlet conditions (including tailwater) are
not factors in determining culvert hydraulic performance.
factors in determining culvert hydraulic performance.
10.In outlet control, culvert hydraulic performance is determined by these factors:

  • Depth of headwater
  • Cross-sectional area
  • Inlet edge configuration
  • Culvert shape
  • Barrel slope
  • Barrel length
  • Barrel roughness
  • Depth of tailwater
11.In short conduits, such as culverts, the form losses due to the entrance can be as important as the friction losses through the conduit. The losses that must be evaluated to determine the carrying capacity of the culverts consist of inlet (or entrance) losses, friction losses and outlet (or exit) losses.
12.The design of a culvert, including the inlet and the outlet,
requires a balance between cost, hydraulic efficiency, purpose, and topography at the proposed culvert site.
Global warming and frequent rainy seasons
13.Headwalls may be used for a variety of reasons, including increasing the efficiency of the inlet, providing embankment stability, and providing embankment protection against erosion. The relative efficiency of the inlet varies with the pipe material used. Figure CU-12 illustrates a headwall with wingwalls.
14.The District does not recommend the use of collapsible gratings. On larger culverts where a collapsible grating is deemed necessary by a local jurisdiction or an engineer, such gratings must be carefully designed from the structural standpoint so that collapse is achieved with a hydrostatic load of perhaps one-half of the maximum backwater head allowable. Collapse of the trash rack should be such that it clears the waterway opening adequately to permit the inlet to function properly without itself
contributing to potential plugging of the culvert.
Damaging the topography