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Why does nobody talk about how suction depth actually drops off in brackish water? | Dredge Operators - Vivisector

Why does nobody talk about how suction depth actually drops off in brackish water?

I was reading an old Army Corps of Engineers report from 1997 last night while waiting for a tow and saw a chart showing a 15% loss in effective suction when salinity drops below 5 parts per thousand. Nobody at our yard ever mentioned this, and I've been running jobs on the Mississippi River delta for 3 years now. Has anyone else noticed their production numbers tanking in low-salinity zones, or is this just me finding excuses for a bad week?

4 comments

4 Comments

amy_martin4mo ago

...so my buddy runs a dredge crew down in Plaquemines Parish, and he called me one night a couple months back cussing up a storm about his numbers being way off. He's been doing this for like 15 years, knows his gear inside and out, but that week his suction depth was just dropping like a rock. Took him forever to figure it out, he had his guys checking hoses and pumps and everything. Turned out they'd moved to a new spot on the river where the incoming tide was mixing with freshwater from a spillway, and the salinity had dropped to almost nothing. Once he realized it was the water itself, he just adjusted his pump speed a little and backed off on the suction head, and things smoothed out. I don't think it's you making excuses at all, that 15% loss the report mentioned sounds exactly like what he saw on his gauges. It's wild how something that small in the water can mess with a whole operation.

stella224mo ago

That's a great real-world example, and it mirrors what my crew saw when we were pumping out a brackish pond last fall.

alice9284mo ago

...but hold on, isn't this kinda backwards though? You're all talking about salinity changes like some mysterious force that only hurts your pump, but what about the guys who actually look for brackish water to get better results? I've seen old timers out here who skip the crystal clear spots on purpose because they know a little bit of freshwater mix can actually help with cavitation in certain setups. They swear by it. So instead of blaming the water, maybe the problem was that your buddy's pump just wasn't tuned for the job in the first place. Ever think that maybe the gauge dropping was just showing him what his equipment actually needed to run right, not that something was broken?

brian_taylor154mo ago

You ever seen a guy spend four hours cussing at a hydraulic pump that wasn't the problem? My buddy runs a little one-man operation on the Gulf Coast, and last spring he pulled into a spot where the water looked clear but felt wrong. He had his whole rig torn apart checking seals and impellers, even called a mechanic from two towns over who charged him a weekend rate. Turned out he was pumping in a zone where a small creek dumped freshwater into the saltwater canal, and his gauges showed suction dropping by a solid 10%. He said once he just throttled down and ran his pump slower, the numbers came back to normal. Made him feel like an idiot for not checking the salinity first.