Reading a Dive Report: What a Good One Contains and a Bad One Hides
By Cheryl Ansel, DOT bridge program engineer, NHI-qualified team leader. Reviewed by Dana Whitcombe, technical reviewer.
Underwater Inspection | Commercial Diving Contractors Alabama Tuesday, 2014. I was standing on the deck of a service barge in the Delaware River, holding a dive report that concluded 'no significant defects' on a bridge pier that I knew was leaning a couple degrees off vertical. I'd spent the morning checking the top-side measurements, and they told a different story. I had two choices: accept the report and close out the inspection, or make the dive team go back in the water. I made them go back. And that's when they found the cracked pile cap that the first diver had missed because he'd been looking through a cloud of silt. That moment taught me a lesson: a dive report is only as good as the diver's ability to see, measure, and write down what he or she actually encountered. In this post, I'll walk you through the structure of a credible underwater inspection report, point out the red flags that tell you a report was worth the paper it was printed on, and suggest what to do when you're not sure. If you're a bridge owner, a consultant, or a regulatory engineer, this will help you save time and maybe a bridge.
What a Good Dive Report Actually Contains
If you're looking at a dive report that's supposed to mean something, start at the top. The first two or three pages should have basic metadata: water temperature at the work depth, visibility in feet (not 'low'), current speed in knots, wave height, date, time, and the name and certification of the diver. I also want to see the equipment list. For most underwater bridge inspections, that means a full-face mask with two-way communication, a 4K video camera in a housing (I like the SeaLife DC2000 for this), a weighted tape measure, a crack comparator, and a hammer. If the report doesn't tell you what was used, you can't evaluate the results. Period. The body of the report should be organized by element. For each pile, pier, or footing, the diver should describe the condition in quantitative terms. '3/4-inch spall at elevation -12.0 ft, face north,' is useful. 'Some spalling' is useless. They should also attach a photo showing a scale. I use a 6-inch stainless steel ruler with a lanyard. The report should also include a statement of limitations: what they could not see, and why. If they couldn't inspect the channel side of a pier due to high current, they must say so. A good report will also state the date and flow rate of the river, because a low water level might expose something that's usually hidden.
The Red Flags That Say 'This Report is Useless'
Let's be blunt. A bad report is easy to spot once you know what to look for. The most obvious red flag is the phrase 'no significant findings' without supporting data. If they didn't measure anything, they can't support that. Another red flag is a report that focuses on generalities: 'the substructure appears sound' or 'minor biological fouling noted.' I need numbers. Also, be wary of reports with a lot of pages but few close-up photos. A wide shot of a pier from 20 feet away can hide a lot of damage. Watch out for 'limited visibility' without a number. If the last 10 feet of a pile is hidden by turbidity, the diver should say so and recommend a follow-up. And if a report includes only edited video clips that jump from clean concrete to clean concrete, I bet the raw footage contains something they didn't want me to see. The opposite is also true: sometimes the footage is unedited and so long that nobody could watch it all, and the report says nothing about the missing sections. Both extremes are bad.
How I Actually Read a Dive Report
My process starts with the cover and ends with the data. First, I check the date, the structure ID, and the location. I've seen reports that were for the wrong bridge. Then I go to the 'findings' table. If there isn't one, I stop. After that, I look at the photos: I want at least three per element, with scale. I compare the condition ratings to the previous cycle. If a crack grew from a hairline to 1/8-inch, I want to know why. Next, I check the bottom elevation and the depth of the streambed. Scour is what kills bridges, and the report has to include a measurement. If the riverbed is 2 feet lower than it was the year before, that's a problem. I also verify the diver's certification and check if the crew had a valid dive plan. For reference, I expect divers to be ADCI-certified, and the inspection team leader should have completed the NHI's underwater inspection course if the work is for a state highway. Here's a digression: once, a dive team said they measured a pile gap with a tape, but I noticed the tape in the photo was only 10 feet long, and the pile was 15 feet below. The diver had made a guess. I made them redo it, and the re-measurement changed the repair list by $200,000. That's the kind of mistake you catch when you read the details.
When to Send a Dive Report Back
If a report doesn't get the job done, I reject it. I literally send it back with a cover letter that says 'insufficient for acceptance.' I'm not being difficult. I'm protecting the public. A vague report is not a deliverable. We've included a clause in our contracts that requires compliance with the NHI manual and the state's own spec. That gives us the legal standing to demand a redo at the contractor's expense. If you don't have that clause, you can still demand better. Ask for the raw video, the diver's daily log, and the calibration records for the depth gauge. If the contractor refuses, you can hire a third-party reviewer. The cost of re-inspection is tiny compared to the cost of a bridge collapse. I've seen it happen, and the consequences are not something you want on your resume.
Frequently Asked Questions
What is the most common weakness in an underwater inspection report? Missing quantitative measurements. Many reports describe deterioration in words like 'significant' or 'moderate,' but don't give crack widths, depths, or exact elevations. Without numbers, you can't make decisions or compare future inspections. How often do bridges need underwater inspection? Under the National Bridge Inspection Standards, most are on a 60-month cycle. But if a bridge has a history of scour, or is fracture-critical, the state may shorten it to 24 or 36 months. Depends on the structure. Can I rely on the summary paragraph of a dive report alone? No. The summary is just an interpretation. The only thing that matters is the detailed data: photos, measurements, and narrative. An engineer needs to see the underlying evidence to assign condition ratings. Why would a dive report say 'limited visibility' but still give a clean bill of health? That's a contradiction. If visibility was poor, the diver cannot reasonably assess all elements. A trustworthy report will clearly state what was not seen and recommend a follow-up, not hide behind the vagueness.