Manaia was twelve, and on Saturdays she ran the lock at Orakei. The lock was a green steel gate on a round concrete pier. The boats waited at the far end of the basin for it. There was a wheel on the harbour wall that wound a sluice open. When the sluice was open the sea came through a culvert under the wall, and the basin came up one slow inch at a time.

Her father Hemi had run it for twenty years. He had taught her one rule on the first morning and never another. “Read both gauges. Then read them again. Then you swing the gate.” There were two gauges. One stood in the basin on a white post with numbers painted up the side. The other was on the sea wall. The tide table was screwed to the wall above it. It showed low water at seven tenths of a metre and high water at two and four tenths.

“I will read them both,” said Manaia. “You will read them both, and you will read them again,” said Hemi. “If they change while you are walking, the second lot is the true lot.”

The launch Te Arahura came in on the Saturday tide with eleven children off a school trip. The skipper put her nose to the pontoon and the children sat down on the wall with their bags between their boots. Manaia wound the wheel. Water came through the culvert making a noise like a hose under a door. She could see the level coming up the basin in one long slow bulge.

It took twenty minutes. She wrote the time in the book. The sluice was still open. She walked out to the white post and read the basin. One metre and eighty. Then she walked to the sea wall and read that. One metre and eighty. Same. She went and swung the gate. It swung easily for three minutes. Then it stopped. Water came over the low sill and pushed the other way. The gate came hard against the stop with a bang you could feel in your boots.

“You had it wrong,” the skipper shouted. “I read both of them.” “You read them once. It was going down. It is always going down here, and you cannot swing a gate on a falling sea.” A fender line snapped and went into the water. It took forty minutes to get the boat in and the children onto the bus. The next tide was six hours away, so the bus came to the road end instead. Hemi found her still at the basin at dark.

“What were the two numbers?” he said. “One metre and eighty. Both of them.” “Read them now.” She read them now. The basin said one metre and eighty-three. The sea said one metre and seventy-nine.

After that the basin was low every morning. Hemi said a basin is never quite full and never quite empty, and to get on with the work. Manaia got a stick with a nail in the end of it and a scrap of paper. She read the post. She wrote the time on the paper. She shut the sluice and set the stick floating and leaned on the wall.

She read the stick every ten minutes. In an hour the water had fallen four centimetres. In the afternoon it fell four more. She wrote it in the book. Basin down four centimetres an hour, sluice shut, gate shut. Hemi read it over her shoulder. “Water does that.” “Water does not do that on the other side of the wall.” She did it again the next day to see if the number was the same. It was.

Hemi called the councilman, because a gate is a council gate. The councilman came on the Wednesday and stood on the pontoon with his hands in his pockets. “This was four centimetres before,” said Manaia. “It is nine now.” The councilman looked at the stick for a long time. Then he wrote nine in the book too, and he wrote the date beside it. “A seal,” he said. “It will be a seal. That is a job for us.” “What will it cost?” The councilman did not say.

At the next high water Manaia wound the wheel and waited twenty minutes. Then she shut the sluice and read both gauges twice before she touched the gate. It swung right round without a bang. She wrote the time in the book. Twenty-four minutes, where last time it had been twenty. The last page of the book has two columns now. One for the tide, one for the seal. Nothing is written in the seal column, because the seal is not fitted yet.