SMO Flow is a Ruby library created by Sebastian Madrid Ontiveros to help support hydraulic modelling in the UK and around the world. It was developed in response to the lack of hydraulic modelling libraries available for Ruby, with the aim of making subcatchment runoff and flow calculations simpler, clearer, and more accessible. The library provides a developer-friendly way to estimate flow from roads, roofs, permeable areas, foul flow, and trade flow, using the Rational Method and timestep-based calculations. If you find this project useful and would like to support its development, please consider donating: https://buymeacoffee.com/smadrid