Eren Tal stood in the center of the steaming alley, his pencil stub gripped between his teeth and a folded sheet of heavy brown wrapping paper pinned against the damp brick wall of the warehouse with his left forearm. He drew a quick, sharp diagram with a piece of red grease pencil, his thumb smudging the wax into the paper grain to mark the grade angles.
‘Look here, Pella,’ Eren said. It spat the pencil stub into his palm and tapped the paper with his calloused knuckle. ‘From the breach behind Karst’s cooperage down to the main under-road drain mouth on Wharf Street, we have a total fall of fourteen feet and two inches over a run of one hundred and twenty yards. That gives us more than enough high-pressure slope to keep the water moving at six feet a second.’
Pella knelt beside him, checking his figures against Hal Rook’s brass measuring tongs. Her fingers were chilled from the damp river wind, but her mind was burning with clear, careful focus. ‘At six feet a second, a twenty-four-inch wide trough with eight-inch sideboards will carry five hundred and fifty gallons a minute. That gives us a twenty percent safety margin over the measured four-hundred-and-fifty-gallon leak.’
