Inspecting a Dam Nobody Had Looked At Since 1978
By Ray Whitfield, ADCI-certified commercial dive supervisor. Reviewed by Amanda McCallister, editor.
Cathodic Protection & Anodes | Offshore & Subsea Diving Water temperature: 48 degrees. Visibility: about four inches. I was on the upstream face of the old Johnstone Mills Dam, depth 22 feet, and my right hand was wedged into a crack I hadn't found on any drawing. Every time the turbine downstream pulled, I felt water moving past my glove. That was the moment I knew why this dam hadn't been inspected since 1978. The dam is a 12-foot-high run-of-river structure on Cattaraugus Creek in Millbrook, Pennsylvania. It feeds a small hydro plant and the village water system. The village board hired me for a routine condition survey—the kind of job you accept when you don't want to admit to your crew that you'll spend six hours in the dark feeling for cracks. The last inspection report I was given was a stack of carbon paper typed on a 1978 date. The names on it were all dead.
How I Got the Call
The village engineer had retired in 1985, and no one knew where the as-built drawings were. The only copy sat in a three-ring binder at the county records office, with coffee stains and a missing page. The board had talked about inspecting the dam for years, but every time someone priced it, they found a reason to put it off. The FERC license for the hydro plant expired, which forced the issue—the new license application required a dam safety inspection. So the board put out a request for proposals. I was the only diver within 200 miles with an ADCI card and a small-boat setup. They paid my site visit, and I remember the foreman who showed me around said, 'Don't fall in,' and meant it. He hadn't been inside the gate chamber since he was a kid.
The First Drop
We launched my Zodiac off the put-in below the bridge at 7 a.m. That September morning. My tender was my nephew, a newly earned ADCI dive medic, which was the closest I had to a qualified crew out there. I was in a dry suit and a brass helmet because the water was cold and dirty. The upstream side of the dam looked different from the postcard version people photograph from the road—it was a wall of green concrete stained with rust, topped with a walkway that hadn't been railed in a decade. As I went over the crest, the water went from clear to chocolate milk. My light made a cone about three feet long before it just gave up. I worked by touch, gloved hands on the face, tracing the outline of the intake trash rack. The rack was a solid sheet of mussels, and behind it the water was silent. That silence is what scares you—you hear the turbine thrumming through the metal, so you know there's power nearby, but you're in a quiet dead zone.
Five Things That Needed Attention
The inspection took two dives over three days, and the report didn't come from any instrument—it came from my hands and a hammer. Here's what I found. First, the intake gate was blocked by a railroad tie wedged in the guide rail. The tie was soft and rotten, but it held the gate open about three inches. That's why the gate vibrated—it couldn't seat properly, and the bypass water was scouring the concrete below it. Second, the concrete around the outlet pipe was honeycombed. When I tapped it with a geologist's hammer, it sounded like a drum—hollow spots. I could flake off a handful of aggregate with my fingers. If rebar corrosion started, the penetration could fail within a decade. Third, the right abutment had settled two inches relative to the center section. There was a crack running along the heel of the dam, and water seeping through it was carrying gray silt, which is never a good sign. That meant soil was leaving the foundation. Fourth, half the anchor bolts on the stop-log guides were missing, and the rest were loose. The stop logs themselves were just a pile of pressure-treated 2x12s leaning against a telephone pole. In a flood, they would have come apart like kindling. Fifth—and this one I almost missed—the date '1978' was scratched into the concrete above the outlet pipe, but the concrete around that inscription was soft, like wet chalk. It had been painted over at some point, and the paint had held in moisture. That was the point where I decided the dam needed a structural engineer's review, not just a dive survey.
What the Town Did
I wrote up the report with photos, video from my helmet cam, and a drawing of the crack locations. The village board met twice. The first meeting they argued about the price; the second they voted to repair the structure from the capital reserve. They dewatered the dam for six days, which meant the creek below ran dry for the first time in living memory. People came down to the bridge to look at the mud and the old machinery that had been underwater for forty years. The contractor worked three shifts and replaced the timber, grouted the void, and installed stainless-steel stop-log guides. The total cost came in under the engineer's estimate. It was a significant chunk of the village's budget, but the alternative—a full replacement—would have been several times that, and it would have broken the water district for a generation. The dam is still there, and I go back every two years now. Last time, I swam the same face and the concrete rang solid.
Frequently Asked Questions
How often should a dam like this be inspected? It depends on state law and hazard classification. A low-hazard dam often falls into a 5-year inspection cycle, but enforcement is spotty. The Federal Energy Regulatory Commission requires a formal inspection for licensed hydro plants, but this one had been unlicensed for years. Can you inspect a dam without draining the reservoir? Yes, a diver can do a hands-on survey and take video. Some problems, like a void in the foundation, require additional testing such as ground-penetrating radar or piezometers. Draining is the last resort, but it gives you a clear look at dry concrete. Is it dangerous to dive near a dam? It is if you're not trained and equipped. Turbulence, entrapment, and confined spaces are real hazards. Commercial divers use surface-supplied air, a tether, and a tender who can pull you out. You never dive alone and you never free-flow into a turbine intake.