The exact math of high-pressure force was an exercise in pure, terrifying reality.
Inside the survey tent, which had been moved to the dry granite bridge pillar beside the Salt-Pan Lock, Nessa Vale sat before her drawing board by the light of three tin animal fat lamps. Across her drafting thick parchment, rows of neat, tiny numbers marched in disciplined columns, calculated down to the third decimal place.
Tomas Reed stood behind her shoulder, nursing an iron cup of hot willow-bark tea. His left forearm was wrapped in fresh linen. The buckled calfskin brace was resting on the bench beside him, his fingers slowly stretching against the rough pine table.
“Read the pressure spreading, Nessa,” Tomas said quietly.
Nessa pointed her brass drafting divider at the cross-section of the central water gate.
“The gate is thirty feet wide and twenty feet tall,” Nessa said. Her voice dropped into the cool, detached register of an engineer studying a bridge failure. “The water behind the timber stands at eighteen feet above the doorstep. That creates a total surface area of five hundred and forty square feet exposed to the pool.”
She tapped the math box in the margin.
“The deep water pressure at the surface is zero,” she continued. “At the bottom doorstep, eighteen feet down, the pressure is seven hundred and eighty-six pounds per square foot. The total level thrust pressing against the bronze guide tracks of the central gate is two hundred and twelve thousand pounds. Over one hundred long tons of static lateral friction.”
Tomas paused at the drawing board, his fingers tracing the contour lines of the upper salt-marsh.
“Explain the lateral spillways, Nessa,” he said. “If the central gate opens, what happens to the dikes on the eastern flank?”
“The eastern dikes are protected by three stonework spill-weirs,” Nessa explained, adjusting her brass sound horn so it pointed toward the open casement where the wind was rising. “The royal engineers knew that when forty thousand tons of water starts moving, the surface forms a standing high-pressure surge. The spill-weirs are graded six inches lower than the earthen crown. If the water level rises above eleven feet during the scour, the excess spills harmlessly into the coastal mud-pans. That kept the earthen dike from being overtopped and washed out. The entire structure is self-regulating down to the half-inch.”
Tomas took a slow sip of the bitter tea. “Can the balance weights lift that much friction?”
“If the bronze rollers in the guide tracks are greased with beef animal fat, yes,” Nessa answered, nodding firmly. “The royal engineers designed the tracks with internal roller-trains—three-inch bronze cylinders housed in grease-boxes. The rolling friction is barely eight percent of the static load. The thirty tons of lead in the balance weight box will lift the gate easily—provided the rollers turn.”
“And if the rollers are seized?” Sile Rook asked from the tent doorway. There, he stood cleaning the hooked steel beak of his hooked pruning blade with an oiled rag.
“If the rollers are seized with dried salt and rust,” Nessa said, looking Sile dead in the eye, “the balance weight will drop, the chain will pull taut. The six-inch bronze winding shaft will shear in two under twisting stress. The balance weight box will crash fifty feet into the dry channel floor, smashing the stonework pier to kindling and leaving the water gate permanently wedged half-open.”
Nessa stood up from her stool. She walked to the tent flap. She looked out into the pitch-black night toward the roaring sound of the wind through the gate towers.
“If the gate is wedged half-open,” she added softly, “the forty-two thousand tons of water won’t flush the fairway. It will squirt through a three-foot gap like water from a broken syringe, scouring out the foundation of the central pier until the entire four-hundred-foot dam collapses into the delta. Sunken Pilings would be washed away in twelve minutes, and three hundred families would drown in their sleep.”
The silence in the tent was heavy as a block of lead.
Apprentice Olla sat by the fire bowl, her goose quill frozen in her hand. Her eyes were wide as she looked at the huge numbers on the thick parchment.
“Then the rollers must be inspected and greased before a single chain is cut,” Tomas said, his voice flat as an anvil.
“That means going down into the roller-boxes,” Nessa said. “Beneath the waterline. In the three-foot drainage gallery between the piers. It’s black as pitch down there, choked with twenty years of salt scale and dead crabs. The water is seeping through the bronze seals at thirty gallons a minute.”
“We have two kegs of fresh beef animal fat,” Tomas said. He rose to his feet and reaching for his wrist brace. “And we have three iron scrapers. Sile, wake Captain Miller and diver Brant. We need two men who know how to work in the dark with four inches of freezing water over their boots.”
Within twenty minutes, Tomas, Nessa, Brant, and Sile had dropped the narrow, upright iron ladder into the underground check gallery of the central pier.
The gallery was a claustrophobic tunnel of cold, glistening granite, four feet wide and six feet high, running horizontally through the base of the pier six feet below the surface of the pool. The air was freezing, soaked with ninety-nine percent humidity. It smelled of wet stone, green slime, and the terrifying, deep shaking of forty thousand tons of water pressing against the six-inch bronze check hatches.
Tomas held the animal fat lantern high. The water on the gallery floor was ankle-deep. It ran in a sluggish, freezing current toward the sump drains.
Nessa knelt before the first bronze roller-box. An oval check plate of two-inch cast bronze, secured by eight heavy iron stud-bolts. She tapped the metal with her scraper.
It gave a dull, dead clink.
“The seal is weeping,” Nessa whispered. She pointed to a steady, thin jet of black marsh water spraying from the bottom seal ring. “The packing is decayed oakum. We have to clear the studs, back off the nuts, and pack forty pounds of fresh animal fat into the roller cage.”
Down in the freezing gloom of the underground check gallery, Tomas’s left arm throbbed with a rhythmic, fiery ache.
The cold salt dampness seeped through his woolen shirt, chilling his skin until the puckered scar tissue across his inner radius felt like an iron band shrinking around the bone. He stopped for thirty seconds, bracing his shoulder against the slimy granite wall, step by step forcing his fingers open one by one against the stone. Thumb to index... Thumb to middle... Thumb to ring... Thumb to little finger. The gristle cracked softly in the dark, releasing the morning adhesion, allowing blood to flow back into his numbed palm.
“Take the light, Tomas,” Sile Rook whispered, noticing the pause. The veteran didn’t offer sympathy. He simply held the animal fat lantern closer to the stud pipe rim, giving Tomas room to reset his grip. “We have four studs left on the lower track. The water is rising an inch every twenty minutes.”
“I have it, Sile,” Tomas said, setting his socket wrench back over the iron nut. “Let’s turn the iron.”
Tomas drew his heavy forged socket wrench from his tool loop. “Brant, take the left stud. Sile, hold the pry-bar against the pipe rim to catch the plate if the water pressure kicks it. Nessa, keep the lantern steady.”
He fitted the iron socket over the first rusted nut. He braced his boots against the slippery granite floor. He locked his hips, his left calfskin brace holding the wrist rigid.
“Heave,” Tomas grunted.
With a sharp, violent screech of rusted threads, the first stud broke free.
Tomas wiped a thick smear of green slime from the bronze nameplate riveted to the center of the check hatch.
The plate was cast in high relief, bearing the royal crest and the stone carving. Heavy SCOUR Rig - SECTOR IV - Approved BY THE Royal CORPS OF WEIRS - YEAR 016. Beneath the crest were stamped the upkeep instructions. Rollers to be flushed with hot animal fat and inspected every ninety days. Failure of lubrication incurs civil penalty of fifty silver crowns per tide.
“Fifty crowns per tide,” Tomas read aloud, his voice echoing through the wet stone tunnel. “Twenty-two years of neglected lubrication. That’s sixteen thousand tides, Sile. The lawful upkeep penalties alone exceed eight hundred thousand crowns.”
“Corve doesn’t have eight hundred thousand crowns, Tomas,” Sile rumbled, his iron socket wrench biting onto the sixth rusted stud. “He has a stone house, forty hired blades, and three stolen barges. But tomorrow morning, we’ll take his stone house and give it to the widows of the men he starved.”
Tomas wiped the grease from his fingers with a dry cotton rag, checking the posture of the bronze cross-head guide one final time. The bronze surface was smooth, unpitted by salt rot. It shone with a pale golden luster beneath the fresh coat of beef animal fat. “The roller cage is seated, Nessa. The clearance is three-sixteenths of an inch across the entire upright stroke. It will slide like an oiled drawer.”
Nessa checked the spirit level mounted to the guide frame, nodding with grim satisfaction. “The track is plumb within one-thirty-second of an inch. When the balance weights drop, the bronze will take the thrust without a shudder. The building will hold, Tomas.”
For four hours, working in the freezing underground dark while the delta slept above them, they labored link by link, stud by stud, packing sixty pounds of dense white beef animal fat into the ancient bronze roller cages, until the rollers turned under their fingers as smooth and silent as spun silk.