The widening of the water chute was a sight illusion born of sound scattering. The South Aqueduct had not reached its terminus, but had entered the first of the great dogleg drain tubes.
These underground drain tubes were crushing pressure-breakers of giant stone scale. To prevent forty thousand tons of racing salt water from smashing the lower quays of the Grand Scroll hall into crushed drift-timber, the First Patriarchs had engineered three in a row ninety-degree curved curves through the dense dark rock foundation of the Southern Shelf. Each curve forced the racing current to climb a banked outer wall of polished stone, bleeding off sixty percent of its dynamic driving force through controlled outward-pulling height.
For a flat-bottomed punt or a light bamboo skiff, the drain tubes were difficult to navigate. For a four-hundred-foot iron-and-oak flagship displacing two thousand tons, each bend was a potential fatal crash.
The physics governing such a huge shifted weight in an enclosed dark rock raceway were merciless. If the vessel entered the curve with not enough speed, the lateral driving force would fail to generate water-flow lift, allowing the four-ton bronze keel to drag along the channel bed and ground the hull. Conversely, if the ship took the curve too fast, the heavy outward pull would overcome the water cushion, driving the upper bulwarks into the overhang of the dark rock ceiling at twenty knots.
