Tainter and Sluice Gate Repair Underwater

By Ray Whitfield, ADCI-certified commercial dive supervisor. Reviewed by Amanda McCallister, editor.

Underwater Inspection | Commercial Diving Contractors Alabama Cold March morning, backwater at the base of a hydro plant. The tainter gate had been grinding against its seal for a week, and I suited up to drop a new rubber seal and reset the wedges. Surface water temp was 41°F, and the gate was 14 feet down, with a 30-foot-deep plunge pool below it. That was a good job, because the hoist could lift the gate clear. Many repair jobs on these gates aren't that nice. You work in the flow, or you work with the gate holding back a few feet of head, and every bolt you turn is working against a column of water that wants to blow through the seal gap. We see a lot of tainter gates and sluice gates at dams, irrigation diversions, and sewage plants. They've got a simple job: move water predictably. When they start leaking or sticking, a diver can often fix them without a shutdown — but only if the operator understands what's possible.

The Difference Between Tainter and Sluice Gates

A tainter gate is the curved radial gate you see on big dams. It pivots at the trunnion, and the curvature means the water pressure holds the seal against the sill. A sluice gate is flatter — often a rectangular blade sliding in a frame. Both have some version of a sealing surface: usually a metal sill and side seals made of rubber, bronze, or treated wood. The failures are different. Tainter gates get leaks at the bottom seal and around the trunnion pin. Sluice gates wear the side guide rails and the bottom seat. And then there's the operator — a stem or hydraulic cylinder that can jam, stripping pins and bolts. We're not making the gate new. We're extending the life until the next scheduled maintenance, or fixing a leak so it doesn't erode the sill. Understand that before you set the first bolt.

Inspection First

Before breaking out the hydraulic wrenches, I rig a video camera on a pole, or if it's murky, I do a systematic hand-feel pass around the seal and frame. I look for gaps, rusted bolts, and whether the seal bar is pitted. If the gate is steel, I can use an underwater ultrasonic thickness gauge to see if the plate is still sound. If it's thin, welding a patch to it is pointless. I also measure the seal gap with feeler gauges — actually, you can't feel much at 30 feet in a 3-mph current. So we use a pressure test with a bleed tap, or a dye test. Call it a learned sense: you spend enough bottom time on these gates and you can tell by the vibration of water through a gap. Then we take that report back to the engineer and decide what we can do from the water side.

The Repair Methods

Seal replacement is the most common. We pull the old rubber or wood seal off, clean the seal plate, and bolt on a new one. That sounds easy — it isn't. The bolts are rusty, often over tightened, and the seal is a long piece with a metal backing bar. I use an underwater impact wrench, and I've learned to prep the bolts with penetrating oil before the dive. Underwater welding comes next. If the sill is cracked or a bearing plate is torn, we can't always bring the dry-dock to the gate. I'm a certified underwater welder, so I'll use Broco-brand exothermic electrodes for salvage work, or stick welding for repairs. But welding wet — even with flux cored wire — tempers the steel, and you can't preheat. So we only weld if the engineer says the metal can take it and the weld won't create a hard spot that cracks later. Then there's the fix that's always awkward: shimming a misaligned wedge. That's what I did on that tainter gate. We loosened the wedge, drove a bronze shim behind it, and retightened. Then we got the gate to close by the hoist, and measured the leakage with a flow meter. It was a fraction of what it was.

Working With the Plant

We aren't the only ones in the water. The plant operator has to give us clearance to work below the surface. That means locking out the hoist, tagging the stop logs, and making sure the intake is protected. Yes, a diver can get caught between the gate and the frame. That's why we never set up without a tender on the surface, and we always have an emergency air supply in case a line gets pinched. The job site water might be raw — sewage, industrial runoff, or cold reservoir water. Our dive bags carry a bunch of spare gloves and wetsuits, and we have a decontamination station if we've been in anything nasty. OSHA 1910.1030 covers bloodborne pathogens, but that's for sewage, which is a whole other ballgame. We follow the plant's site-specific safety plan. If there's any chance of gas, we've got a gas monitor on the surface. And for the plant manager who's thinking about cost: an underwater repair is almost always cheaper than dewatering. But not always. If the gate is too far gone, or if the holding bolts are in a location you can't reach from the water side, dewatering and a dry repair is a better bet. A good diver will tell you that.

Frequently Asked Questions

How long does an underwater gate repair take? Depends on the gate and the damage. A seal swap can take a six-hour dive. Replacing a section of sill plate might take two days of bottom time if you're welding. Give or take. Can a gate be repaired while the water is still flowing? Sometimes. We often work in flow velocities up to 1-2 m/s, but any faster and the diver needs to be behind a cofferdam or the gate is partially raised. If the leak is bad, we'll set a temporary patch. How much does it cost? There's no flat rate. You're paying for a dive team, a decompression chamber on site, plus time and materials. The model is day rate plus consumables. It's usually less than dewatering a dam. Is underwater welding safe and reliable? Yes, when done by a certified diver/welder with the right electrode and the engineer's sign-off. It's not as strong as a dry weld, but it holds for a maintenance period. We never weld on a thin or corroded plate.