Garonne · official main stem

Gauge coordinates and current discharge come from the named national hydrometric networks. The shared distance axis projects those GPS stations onto the dashboard’s sparse upstream-to-outlet spine; this is a profile axis, not surveyed navigation kilometre. The bed is published operator gauge datum throughout. A station whose register publishes no datum is left off it rather than given the spine’s interpolated height, which on a concave long profile sits well above the real bed. Where one register republishes another’s station, the two rows are one gauge and only the fuller record is plotted. River power is gravitational power carried by the flow (ρ·g·Q·Δh), not metered generation - it is a floor rather than a total, because a reach whose downstream gauge reports no discharge contributes nothing. The navigability line is an indicative planning threshold, not an official fairway forecast.