Chapter 113: Which Face Gets the Clay

Nobody moved a stone for the first eleven days.

They moved water, which Leon had said in the winter would be necessary and which half the settlement had heard as an excuse.

The narrows are two limestone shoulders sixty paces apart with the whole river between them, and you cannot lay anything on a bottom that has a river running over it. So the first job is to send the river somewhere else for a while.

Oren built it out of stakes, brush and clay, in a curve, pushing the flow into the western third. Eleven days and thirty people, and it is not a dam and was never meant to be one. It leaks constantly and somebody stands on it all day with a basket.

What it does is take the eastern side from thigh-deep and moving to knee-deep and slow, which is the difference between work and nothing at all.

Halu opened his column on the first morning.

Who was in the water. How long. And whether they were worse the next morning than they were the night before.

***

The undercut is worse than anybody who had not knelt in it believed.

Fel's survey said two paces back under sound rock. It is two at the deepest and about one and a half across most of the face, and all of that space is packed with soft grey silt that has been going in there for longer than the cord.

You cannot see it. Even at knee-deep the water is grey inside four minutes of anybody touching the bottom, and it stays grey.

So it is done by hand, kneeling, arm in to the shoulder, filling a basket by feel, and the basket goes back along a line of people to the bank.

Leon did nine days of it and was slower than the fourteen-year-olds, and lost the feel in his fingers by the ninth hour every day, and Halu had him out of the water twice in the first fortnight, both times correctly.

What he did contribute in that fortnight was a stick.

A straight pole, marked at a hand and two hands and four, so that whoever was clearing could push it into the void and say a number instead of a long way. Kel ruled a page with sixty positions across the face, one every finger's width along a pegged cord, and every position got a number twice: once at the start and once when they thought they were finished.

It is not clever and it took an afternoon, and it is the reason anybody knows the void was cleared: the second number is smaller in fifty-eight of sixty positions, and the two that were not got done again.

***

The argument happened in the third week and Leon nearly lost it, and losing it would have been a disaster that arrived in about nine years.

The fill goes in graded. Biggest stone at the bottom, hard against sound rock at the back, then smaller, then smaller, so the little ones lock the gaps in the big. A wall of one size of stone is a sieve with pretensions.

Nobody argued with that. Oren had worked it out himself on the wall years ago in a different form and said so.

The argument was about the clay.

There is a good bed of clay below the second bend and they had been carrying it up for a fortnight. It goes on the face, packed and rammed, sealing the fill so water cannot get in among the stones and start moving them.

Oren wanted it on the downstream face.

His reasons were good. It is the face you can see from the bank, the face you can get at to repair in a hurry, and the face the water comes off, and water coming off a thing is what tears it up.

"Upstream," Leon said.

"You cannot get at it upstream. It will be under three feet of water eleven days after we finish."

"Ei. That is why."

***

He explained it badly twice and got it right on the third go, by not talking about pressure at all.

Water pushes. It pushes from the upstream side, always, at everything.

Put the clay upstream and the river spends four generations pushing it into the stones. Every flood packs it tighter. A crack in it fills with silt by itself because the water is carrying silt and going that way.

Put it downstream and the river spends four generations pushing water through the stones from behind and out against the clay, which is then the only thing holding, and the first time it lifts anywhere the water goes through and takes the face off in one night.

"And the stones behind it?"

"Have to be able to let water out. If water gets in and cannot get out you have built a bag." Leon put his hands together and pulled them apart. "The back of it must drain. The front of it must not let water in. If you put the tight part at the back you have it exactly the wrong way round and it will stand for eleven years and look perfect the whole time."

Oren listened to all of it, which took some doing, because he has been building things on that river since before Leon was born on another planet.

Then he said the thing that made Leon like him properly for the first time.

"I do not believe you."

***

So they tested it, because that is what this place does now, and it cost two days and nine people and it is the reason the weir will still be there in a hundred years.

Two trial walls in the side channel below the eastern shoulder, a little over two paces long and knee high, built the same way out of the same stone by the same four people on one afternoon.

Clay upstream on one. Clay downstream on the other.

Then they broke the diversion open a hand's width and let a real flow at them for two days, and Kel sat on the bank with a page and the children took turns measuring how far the water came out on the low side.

The downstream-clay wall passed water from the second hour and was undermined at one end by dusk. The children measured the leak dropping, which everybody misread as a good sign for about an hour, until Oren worked out it was dropping because the wall was settling into the hole it had dug for itself.

The upstream-clay wall leaked for about four hours, and then leaked less, and then stopped, because it had silted itself shut.

Oren went and knelt in front of it and put his hand on the clay face and stayed there a while.

"It got tighter."

"Ei."

"On its own. With nobody doing anything."

"That is the whole reason to put it there." Leon crouched down beside him. "Everything else on this weir gets worse every year and wants forty people to come back and fix it. That gets better every year on its own, and it will go on getting better after everybody who built it is dead, and that is the only part of this that is free."

Oren stood up, looked at the two little walls a moment longer, then went and got Fel, and made him look at both, and made Kel read out the numbers, and did not say one word about who had been right.

He did not have to. Doran wrote it down.

Tested. Two walls, two days, in the side channel. Clay upstream. Oren said he did not believe it and asked to be shown, and that is why it is known and not merely said.