Stormwater Runoff API
Stormwater-runoff civil-engineering maths as an API, computed locally and deterministically. The rational endpoint computes the peak runoff from a catchment with the Rational Method, Q = C·i·A — in metric form Q(m³/s) = C·i·A/360 with rainfall intensity i in mm/h and area A in hectares, or in US form Q(cfs) = C·i·A with intensity in in/h and area in acres — where the runoff coefficient C is the fraction of rain that runs off (about 0.9 for paving and 0.2 for lawns). The time-of-concentration endpoint computes how long water takes to flow from the most remote point of the catchment to the outlet with the Kirpich formula, tc = 0.0195·L^0.77·S^(−0.385) minutes, from the flow-path length and slope; this sets the design-storm duration. The detention endpoint gives a first-order estimate of the detention-pond storage needed to throttle a peak inflow down to an allowable outflow over a storm duration, (Q_in − Q_out)·duration. Coefficients are dimensionless, intensities in mm/h or in/h, areas in ha or acres, lengths in m and flows in m³/s. Everything is computed locally and deterministically, so it is instant and private. Ideal for civil-engineering, drainage, urban-planning, landscape and flood-risk app developers, sewer-sizing and detention tools, and hydrology education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is stormwater runoff; for open-channel flow use a Manning API and for pipe friction a Darcy API.
api.oanor.com/runoff-api
