09 Stormwater

Builds a design-storm hyetograph from an IDF (Intensity-Duration-Frequency) curve, with an optional climate allowance. Feed it to Stormwater Run. Give it EITHER the three coefficients of an i = a/(t+b)^c fit, OR a published depth-duration table (the form NOAA Atlas 14, KOSTRA and FEH actually distribute). The alternating-block and Chicago patterns reproduce the IDF depth at every sub-duration, which is what makes the result a design event rather than a shape.

Fetches land-cover polygons around a lat/lon from OpenStreetMap (open data, no key) and classifies each into a Curve Number and an overland Manning's n. This is the same Overpass query the Land Cover Roughness component makes, read for runoff instead of for wind — so wiring both on one site costs one fetch, not two. Unmapped tags are skipped rather than guessed at.

Tags an area of the site with how rough it is and how much rain it sheds. Manning's n here is the OVERLAND FLOW value, several times the channel value for the same material — at the millimetre depths of sheet flow the surface texture is the whole channel, and using a channel roughness makes runoff arrive far too fast. A Curve Number (1–100) models losses that grow through a storm as the ground wets up; leave it at 0 to use the flat runoff coefficient instead.

Turns a stormwater result into meshes and numbers. This is the ONLY component that materialises the field — a run holds millions of values and emitting them all as a tree would freeze the canvas, so ask here for the field and the time you want.

Rasterises the graded terrain into the DEM the solver runs on. Buildings become no-flow WALLS rather than raised ground: raising them fabricates a ridge at the footprint edge that sheds water in whatever direction the rasterised edge happens to face, and lets water pond on roofs. Breaklines are how a 1 m grid stays usable. A kerb, a swale invert or a threshold is sub-cell at 1 m and every one of them controls where the water goes — sampling the terrain at cell centres averages them away. Burning them along the cell path keeps the control without paying for a fine raster over the whole site.

Routes a design storm over the graded terrain and reports ponding depth, flow velocity and flood hazard. Two modes. FAST is terrain analytics only — slope, flow direction, contributing area and the capacity of every depression — which recomputes between grading edits and answers most of a grading review. FULL adds a shallow-water solve for the depths and velocities a design storm actually produces. SURFACE ROUTING ONLY: no pipe network, no soakaways, no evapotranspiration. Use it for design-storm and cloudburst checks, not for hydraulic sizing.

Solver controls for Stormwater Run. The defaults suit a 1–5 m urban raster; leave this unconnected unless a run misbehaves.

One row per puddle: where it is, how much water, how deep, when it peaked and how long it took to drain — against the capacity of the hollow it sits in, so an overflowing depression is visible as such.

Traces where the runoff goes, as curves over the graded surface. From a full run these are the solved velocity paths; from a fast run they are steepest-descent paths down the depression-filled terrain.

A legend for a stormwater mesh: swatches, labels and a title, placed on a plane.