Survey Requirements for Pipe Culverts

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Detailed Description

This video demonstrates how to measure various aspects of pipe and pipe-arch culverts for culvert indirect measurements. The video includes tips and tricks for measuring the geometry, corrugations, and entrance types including rounded or beveled entrances.
 

Details

Image Dimensions: 4608 x 3456

Date Taken:

Length: 00:04:41

Location Taken: Las Vegas, NV, US

Video Credits

 

Todd Geiger, Megan Poff, Terry Kenney, Office of Employee Development, Ruby Hurtado
 

Transcript

Hi, this is Chris Morris and I’m the surface water specialist at the USGS in Las Vegas, Nevada. I will be talking about surveying the geometry of pipe and pipe-arch culverts. In previous videos I discussed surveying the approach high water marks, the tailwater high water marks, an approach cross-section, and the general attributes of any culvert. The information presented in this single-component video can also be found in TWRI 3-A3, Measurement of Peak Discharge at Culverts by Indirect Methods.

As mentioned in previous videos, good clear notes are needed. With complex culverts or when combined with other methods (say a road overflow) it is easy to forget to measure the beveling or note if you measured the top or bottom of the culverts. There is nothing worse than finding that a critical element was missed a few months ago, and an additional site visit or survey is need to finish the computation. Even for someone who has surveyed many culverts, I find having a checklist is useful to get everything you need.

I typically wait to do the following steps after I am completely finished with the survey. Although all of these could be done during the survey, I find you are less likely to mismeasure or not note an important element if you aren’t doing two things at one time. Additionally, some of these are easier to measure with two people.

First, let’s determine the area. For a circular pipe, the diameter should be measured (remember geometry class…we can compute area from the diameter). I typically will measure at least a couple diameters, both vertically and horizontally using a measuring tape. Sometimes corrugated metal pipe culverts can become squeezed out of circular due to traffic on the road, becoming more like ovals. Such pipes and pipe arches (that are made that way) should have both a rise and span measured. The key is to try and do our best to compute the area of the pipe.

For concrete pipes, I will measure the inside diameter and the thickness at the top if I ended up surveying the top rather than the bottom. For corrugated pipes, the inside diameter should be measured… this is the distance from the most inside portion of the corrugation on one side to the other side....ie the minimum inside diameter

For the next few steps, we will most likely be measuring and noting the conditions of various small elements of the culvert. These are the ones most likely to be missed. These various elements will be used to determine adjustment factors for various coefficients during the actual computation.

The material used to make the pipe should be noted and photographed. Typically, it will be concrete or corrugated metal. For corrugated metal pipes you also need to measure the size of the corrugations. First, I measure the width by using a folding ruler to measure the distance between two adjacent high points. Next, I measure the depth by putting the folding ruler into a low point and using a small hand level or a straight edge to line up the two high points. For a standard corrugated metal pipe, these are 2⅔ inch width and ½ inch depth, however, other sizes may be encountered.

Next, let’s focus on the entrance. Depending on the culvert, it may or may not project or stick out from the embankment. If the culvert does not project, it should be noted and photographed. Sometimes pipes are mitered, or cut at an angle to match the slope of the embankment. If such a pipe does not project, it should be noted and photographed. If the culvert is thick walled (such as concrete), even if it does project, it should be noted and photographed, but no additional measurements are needed. However, if the culvert is thin walled (such as a corrugated metal pipe) the projection needs to be measured.  Typically, if the culvert is projecting, the embankment it is projecting from is uneven. I measure the projection on the top, the bottom, and both sides. I will later average these values to determine the projection used for the adjustment factor.

The final factor to examine are the culvert walls at the entrance. They can be squared, rounded, or beveled. For rounding, the culvert walls will be rounded on the side at the entrance. I measure this by using a small hand level or another straight edge to line up flat on one side and a folding ruler flat on the other side. In between, there will be a gap from the 90-degree corner created by the two tools and the rounded corner of the culvert. I then measure the distance on the folding ruler from the hand level to where the culvert wall is again parallel with the folding ruler (this is where the gap ends). Repeat this step by switching the positions of the straight edge and folding ruler. The average of the two values, is the radius of the entrance rounding.

With a culvert entrance that is beveled, the culvert wall entrance has corners not at 90-degree angles. To measure the bevel you need to measure the angle as well as the thickness of the wall. I measure the angle by using a protractor facing away from the bevel. Then I line up the folding ruler with the bevel and read the angle between the ruler and the wall. This should be done at all bevels since they won’t necessarily be the same on all sides. Sometimes only the top of the culvert is rounded or beveled. If the flow being computed did not reach this height, it is not necessary to measure, although could be used for future computations.

If you need help in the field, call your supervisor, surface-water specialist, or indirect measurement specialist.