TITLE
The Aldwyn, Source to Sea

PROMPT
A horizontally scrolling illustrated journey down an invented river, "the Aldwyn", from a spring on a moor to the open sea: 138 kilometres as one continuous panoramic drawing that the reader travels along sideways. Vertical scroll input (wheel, trackpad, touch swipe up/down as well as sideways, keyboard) is translated into horizontal travel, with no native horizontal page overflow on any device. Concept: a river as a sentence read left to right; one unbroken ribbon of water.

Mood: fresh, observant, affectionate; an illustrated children's-atlas for adults. Palette: pale meadow paper #EAF2E3, river blue #2F6690, leaf green #3A7D44, buttercup yellow #F4B942, deep bottle-green ink #254441 for outlines and type. Flat, limited-colour illustration in SVG with a consistent line weight, texture from simple hatch patterns, no gradients except in the water. Light page.

Structure: a fixed viewport-height stage containing a very wide SVG world (about 9–11 viewport widths on a desktop screen, proportionally more on a narrow phone, since the drawing is scaled to the stage height) translated horizontally according to scroll progress (a tall scroll container with a sticky stage). Three parallax layers: distant hills and sky (slow), the river and its banks (base speed), foreground reeds, fence posts and birds (fast). The river itself is one continuous path that begins as a thread and widens steadily to fill the lower third at the estuary; it is always on screen.

Stations along the way (each with a small typeset caption block and a kilometre marker in the form of a white-on-green river sign; captions specific and lightly witty, 25–45 words): km 0, the spring at Hob Moss: a trickle under cotton grass, a curlew; km 6, the first waterfall, Grey Mare's Step; km 17, a packhorse bridge and a dipper bobbing on a stone; km 31, the old mill at Farrow, with a turning water wheel; km 48, water meadows, cows standing in the shallows, a heron; km 63, the town of Aldwynbridge: a weir, terraced houses, a brewery chimney, a rowing eight passing, anglers; km 80, a lock and a narrowboat rising in it; km 97, the reservoir intake and a pylons-and-poplars stretch; km 115, the tidal limit: mudflats, moored boats leaning, waders; km 131, the docks: cranes, a rusty dredger, a ferry; km 138, the bar and the open sea: a lighthouse, a line of surf, and the river's blue dissolving into a wide horizon.

Life and motion: water flows: animated dashes/ripples moving downstream along the river path at a speed that changes with the gradient (fast and white at the fall, slow and broad at the estuary); the mill wheel turns; the narrowboat "Patience" rises in the lock as the reader scrolls through that stretch (scroll-linked water level and gates; the camera slows there), leaves upstream, and the chamber then empties again with the paper boat inside; birds fly when approached; rain crosses the moor at the start, sunlight at the meadows, an evening tint by the sea (the sky layer shifts hue along the journey). Signature moment: a small paper boat (folded, white with a yellow flag) launched at the spring that rides the current the whole way: it stays near the viewport centre, bobbing and rotating with the flow, tumbling over the waterfall, spinning in the mill race, waiting in the lock, dodging the rowing eight, and finally heading out past the lighthouse; if the reader stops scrolling it drifts on a little and circles in an eddy.

Navigation aids: a fixed slim strip at the bottom: the entire river in miniature as a line with station dots and the boat's position, clickable to jump (smooth animated travel); an altitude profile above it falling from 520 m to 0; a readout: "km 48 · 71 m above the sea · flow 9 m³/s" (invented but consistent, increasing downstream), with the name of the current reach beside it on wide screens; and a small designed sound toggle (off by default) for a synthesised water noise that swells at the fall, the weir and the surf. The opening screen: title lettered large in a hand-drawn-feeling serif italic (Palatino/Georgia italic) "The Aldwyn" with "source to sea, 138 km" and a designed cue: an arrow made of flowing dashes and the words "scroll: the river does the rest". End screen: the boat on the open sea, a low sun with a glitter path, and a line: "It took the water eleven days. You were quicker." with a "Back to the spring" button.

Typography: captions in a book serif with small-caps place names; kilometre signs in a bold condensed sans; a few hand-lettered labels along the bank set on curves (SVG textPath) for tributaries ("Farrow Beck"). Touch: vertical and horizontal swipes both travel; a mouse can also drag the landscape; keyboard: arrow keys and Page Up/Down move along. Phone: stage height fits the viewport; captions sit in the upper third. Reduced motion: no parallax or water animation; the view snaps from station to station and the boat simply appears at each one.

DESCRIPTION
A sideways journey down an invented English river, drawn as one continuous flat-colour panorama in the manner of a children's atlas for grown-ups. The page opens in rain on a moor, with the title lettered large in rough-edged Palatino italic and a paper boat dropping into a spring no wider than a pencil line. Scrolling carries the reader 138 kilometres downstream: over a gritstone fall, under a packhorse bridge, past a turning mill wheel, through buttercup meadows, a terraced brewery town, a working lock, pylons and poplars, mudflats, docks, and finally past a lighthouse into an evening sea. The river is a single unbroken blue path that widens from a thread to the whole lower third of the stage, and the little boat rides it the entire way, behaving differently at every obstacle. Each of the eleven stations carries a white-on-green kilometre sign and a short, dry caption; a slim strip along the bottom shows the whole river in miniature with an altitude profile and a live readout of distance, height and flow.

VISUAL TECHNIQUES
- One viewport-sized inline SVG whose layer groups are translated at different rates (distant fells 0.18, rolling country 0.4, clouds 0.22, river and banks 1, foreground reeds, fences and railings 1.5) from a single eased camera value driven by vertical scroll in a tall track with a sticky stage
- Geometry computed in the page: cosine-interpolated river centreline, width and ground-line functions produce the river polygon, banks, bank hachures, hedged field patchwork, far ridgelines and the minimap from the same data
- Strict five-colour palette with tints mixed in code; consistent 3-unit ink outlines; texture from SVG hatch, brick, dot, grass and buttercup patterns; gradients used only in the river and sea
- Flowing water as dashed flow lines per reach whose dash-offset speed and dash length follow the gradient (fast and white at the fall, long and slow in the estuary), plus an animated fall, weir, mill race and surf line
- Scroll-linked lock choreography: chamber water level, mitre gates, the narrowboat's rise and exit, and the paper boat's wait, entry and descent are all functions of camera position, with the camera slowed through that stretch
- Paper boat behaviour model: follows the river slope, tumbles through 360 degrees over the fall, spins in the mill race, jolts over the weir, sidesteps the rowing eight, bobs harder at sea, and drifts on into a circling eddy when scrolling stops
- Weather and light along the journey: animated rain pattern and hatched storm clouds on the moor, a rayed sun over the meadows, sky colour interpolated to a buttercup evening, a setting sun with a glitter path on a sea that the river's fill fades into
- Approach-triggered birds (curlew, dipper, heron, waders, gulls, wagtails) with two-frame wing animation; turning water wheel, luffing cranes, crossing ferry, chimney smoke, rocking buoys, a pulsing lighthouse lamp
- Hand-lettered map labels on curves with SVG textPath; a turbulence displacement filter roughens the title and end line; a fine paper grain overlay
- HTML captions and title travelling with the landscape; group culling of off-screen scenes; reduced-motion mode that snaps between stations

INTERACTION MODEL
Scrolling down (wheel, trackpad, touch swipe, Page Down, Space, arrow keys) moves the camera to the right along the river; scrolling up goes back upstream. Horizontal trackpad gestures, horizontal touch swipes (with a little momentum) and mouse dragging on the landscape travel the same way, and Left/Right arrow keys nudge along. The paper boat stays near the centre of the view and reacts to whatever stretch it is in; stop scrolling and it drifts a little ahead and circles in an eddy. Birds take off as the boat approaches and return once it has gone well past. At the lock the journey slows: the water level, gates and boats are tied directly to scroll position and can be run backwards. In the bottom strip, any point on the miniature river can be clicked to travel there with an eased animated journey, and each station dot is a focusable button with a name tag on hover or focus; the boat marker, the dots and the readout update continuously. A round button in the strip turns a synthesised river sound on and off (off by default). The end screen offers a button that sails the view back to the spring. With reduced motion requested, the view snaps from station to station with a brief fade and the arrow keys step between stations.