Survey Requirements for Box Culverts

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Detailed Description

This video details how to measure various aspects of a box culvert for a culvert indirect measurement. The video includes tips and tricks for measuring the geometry, wingwall angles, and entrance types including rounded or beveled entrances.
 

Details

Image Dimensions: 4288 x 3216

Date Taken:

Length: 00:03:50

Location Taken: Henderson, NV, US

Video Credits

 

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

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 a box culvert. In previous videos I discussed surveying the approach high water marks, the tailwater high water marks, and 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 of 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 that has surveyed many culverts, I find having a check list is useful to get everything you need.

I typically wait to do these steps until 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 an area. For a box culvert, the width and the height should be measured. Be careful, not to include the width of the walls.

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 culvert should be noted. Typically, it will be concrete, but other materials are possible for a box culvert. It should be noted and photographed.  

Next, let’s focus on the entrance. Depending on the culvert, it may or may not have wingwalls. Although the length of the wingwalls are important for locating the approach cross-section, we are now focused on their angle. The angle you want to measure is the one between the culvert entrance, perpendicular to the flow, and the wingwalls. The easiest way is to measure this directly. Put a protractor on top of where the culvert and wingwalls come together and measure the angle. Be careful when you are this close to an edge. The use of fall protection equipment may be needed. Another way you can measure the angle is to place a protractor perpendicular to flow at the upstream end of the wingwall (so 0 degrees points to one bank and 180 degrees to the other bank. Now use a straight edge to line up with the stream side of the wingwall and so it projects upstream. The angle on the protractor at the straight edge on the bank side will be the same angle as at the culvert entrance.

The final factor to examine are the culvert walls (not the wingwalls, the actual walls of the culvert). They can be 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 the 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 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. I then 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 it may be used for future computations.

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