Interactive engineering model
TR-55 travel-time watershed path
Follow a water parcel from the divide to the outlet as one flow path converges from a sheet-flow film into a swale or gutter and then a channel, each reach crossed at its own travel speed.
Preparing the 3D model...
A hillslope terrain block is cut by a single flow path, and one continuous water body narrows and deepens through the sheet-flow apron, the shallow concentrated swale or paved gutter, and the trapezoidal channel. Sprite labels give each reach its length, slope, and travel time, and the parcel crosses each reach at that reach's own velocity, so the slow sheet reach and the fast channel reach read as speed and not only as numbers. The published TR-55 sheet-flow maximum is 300 feet; 100 feet is identified as a common local screening limit, and any length entered beyond 300 feet is drawn but hatched and left out of the sheet travel time.
Focus the 3D view and use the arrow keys to orbit, plus or minus to zoom, and Home to reset the view.
Text explanation and non-WebGL fallback
A hillslope terrain block is cut by a single flow path, and one continuous water body narrows and deepens through the sheet-flow apron, the shallow concentrated swale or paved gutter, and the trapezoidal channel. Sprite labels give each reach its length, slope, and travel time, and the parcel crosses each reach at that reach's own velocity, so the slow sheet reach and the fast channel reach read as speed and not only as numbers. The published TR-55 sheet-flow maximum is 300 feet; 100 feet is identified as a common local screening limit, and any length entered beyond 300 feet is drawn but hatched and left out of the sheet travel time.
The numeric controls and readouts remain usable if WebGL is unavailable. Drag or swipe the 3D view to orbit and use a wheel or pinch gesture to zoom. With the 3D view focused, use the arrow keys to orbit, plus or minus to zoom, and Home to reset. The complete numeric lesson is also keyboard-accessible in the adjacent controls and readouts. This model is an educational aid and does not replace applicable design standards or professional review.