OXBOW — How the floodplain was built

01 · The concept

A river's whole restless century, in one aerial frame.

A single quiet instrument for anyone who has stared at a satellite image of a lowland river and wondered why it wriggles. Its one job: make meander migration — normally invisible, a metre or two a year — legible, by compressing a hundred years into minutes. You watch bends fatten, banks erode, point bars build, and every so often a neck pinch off and strand an oxbow lake. The plain keeps the record: faint scroll-bar scars mark every channel the river has already abandoned. The register is cartographic and calm — a survey sheet that happens to be alive.

02 · Palette

Four colours, argued from the plain.

Read as an aerial map at noon: a green floodplain, silt-laden water, pale sand where the current drops its load, and a dark levee ink for every word. The bright accents stay on marks — the channel, the trace line — while text runs in darker ink tokens so nothing sits below 4.5:1, even over the animated map.

#7C8A5A · floodplain greenThe plain itself — vegetated silt, the ground the river cuts across.

#4A6E70 · silt-waterThe channel and the stranded lakes. Its darker #38565A carries any small type or link.

#D9C79A · sandbarPoint bars on the inside of bends, and the pale rims of abandoned channels.

#3E4A2E · levee inkBody copy and labels. A deep bank-shadow green, never pure black.

#EDE7D4 · loess paperPage ground — pale wind-blown silt, so the green map reads as a distinct survey pane.

#2A3018 · deep inkHeadlines and the wordmark. The darkest green in the valley.

03 · Type

A survey serif and a field-note sans.

Display · Fraunces · opsz 40–120 · 500–600

A neck pinches off

Fraunces has the warm, slightly literary voice of an old geographical survey — soft terminals, a real italic for emphasis, and optical sizing so the giant "OXBOW" tightens while section heads stay open. The typographic bravery is the italic stranded and lake — the words that name the whole event set apart in the water colour.

Labels · Work Sans · 400–600

YEAR 74 · 2.83× · 4.3 m/yr

Every measured thing — the year count, sinuosity, migration rate, channel length — is set in Work Sans. It reads as instrument output: neutral, tabular, honest against the soft serif, and legible at label sizes over the map.

04 · Technique

The signature: a curvature-driven river, canvas 2D.

No libraries. The river is a polyline of ~300 nodes rendered on a <canvas>, migrating under a simplified Ikeda–Parker–Sawai meander model. Each step computes the signed curvature at every node, then moves the centreline along its normal by an amount weighted by an exponential kernel of upstream curvature — the same physics that makes real bends both grow and lean downstream. Crucially the migration erodes the outer bank (the sign matters: get it wrong and the river relaxes straight instead of meandering). After each step the line is re-sampled to even spacing and lightly smoothed to suppress grid-scale kinks.

The cutoff is the payoff. Every step scans for two non-adjacent nodes that have drifted within a neck's width of each other; when they touch, the loop between them is spliced out of the channel and pushed onto a list of oxbow lakes, drawn forever after as a still crescent that greens and shrinks as it silts in. That's why nothing is scripted — a lake is stranded only when, and where, a neck actually closes. The sinuosity trace on the panel is the honest fingerprint: it climbs as bends fatten, then drops one step the instant a cutoff shortens the channel.

The floodplain is a second, never-cleared canvas. Every year and a half the live channel is stamped onto it at low alpha, so the plain slowly accumulates the ridge-and-swale scars of every position the river has held — the second-read detail, a map building underneath the map. Point bars are drawn from each node's acceleration vector, which points into the concave bank exactly where sand deposits. DPR is capped at 2, the loop pauses when the tab is hidden, and holding the pointer over the map freezes the century so you can study a single moment.

05 · Iteration log

Working, then premium.

Pass 1Craft

Fatal first: the initial migration ran the wrong sign — bends relaxed to a straight line (sinuosity pinned at 1.00, zero oxbows) and the headless probe still saw a "live" canvas. Flipping the erosion to the outer bank brought the whole signature to life.
Made the units honest: set 16.5 m per virtual unit so the stated "valley is 15 km" matches the sinuosity maths exactly (channel ÷ valley).
Calmed the floodplain texture to broad, low-alpha mottle, and widened the cutoff threshold so loops strand clean crescents instead of tangling into tight spirals.
Reserved the water accent for marks; every small label runs in the levee-ink token, verified ≥4.5:1 over the map.

Pass 2Depth

Enriched the signature: oxbow lakes now silt in over ~130 years — fresh cutoffs read as deep still teal, older ones green and thin toward the plain, each ringed by a pale abandoned bank and a damp-meadow halo.
Added a hold-time micro-interaction: hovering (or pressing) the map freezes the migration and the tag reads TIME HELD, so you can stop the century mid-cut and study it; releasing resumes cleanly.
Second-read details: the never-cleared scar layer, the deep-water glint down each fresh lake, and a live sinuosity trace whose sawtooth marks every cutoff with a dashed line.
Blended a small local-curvature term into the migration so cutoffs distribute along the reach rather than piling up at the downstream end.

Pass 3Hardening

375px: map and panel stack full-width, the compass hides, readout stays a 2-up grid — verified the wordmark and nav sit inside the viewport box, not merely that scrollWidth ≤ 375.
Reduced motion: the model runs synchronously to a rich mid-century frame (a river already meandering, a lake already stranded) and never starts a rAF loop; the hold interaction is disabled.
Resilience: DPR capped at 2, resize rebuilds the plain and re-stamps existing scars, the loop pauses on visibilitychange, and a clamped delta stops the century lurching after a tab-away. Removed the redundant valley-fabric strokes (Chanel rule) — the meander scars already carry the texture.