Chapter 8 is recursion, and the classic example is a branching tree. River networks branch the same way, so this expansion sizes the branches with real river flow.
The page fetches instantaneous discharge (cubic feet per second) from four USGS gauges in the Colorado River basin. The tree’s top-level branches each take their thickness from one gauge’s live reading, and the recursion carries a share of that flow down into the sub-branches. The result is a living hydrograph: after rain upstream, the limb fed by that gauge visibly fattens. Line color shifts with depth so the trunk and twigs read differently.
Data source: USGS Water Services (instantaneous values)
Endpoint:https://waterservices.usgs.gov/nwis/iv/?format=json&sites=09380000,09315000,09180500,09379500¶meterCd=00060
Access: Public, no key. Loaded from an hourly server-side refresh when possible, with a bundled snapshot fallback, and a live browser fetch only when the API allows CORS. Data window: Jul 17, 2026 (pulled Jul 18, 2026 UTC)
Click the sketch to redraw with fresh random branch angles over the same live flow values.