Getting Started with 2D HEC-RAS: From Terrain to Flood Maps

HydroLearn Getting Started with 2D HEC-RAS: From Terrain to Flood Maps Getting Started with 2D HEC-RAS: From Terrain to Flood Maps View Course Problem statement When heavy rain hits a town, the questions that reach the forecast desk are spatial: which neighborhoods flood, how deep, and how fast is the water moving? A stage forecast at a single river gauge cannot answer them. A two-dimensional (2D) hydraulic model can: it takes the terrain and the rainfall and returns maps of flood depth, velocity, and water surface elevation that civil protection can act on. The tool most agencies reach for is HEC-RAS , free software from the US Army Corps of Engineers Hydrologic Engineering Center, used worldwide. Two obstacles keep early-career staff away from it. First, the interface: three separate working windows and a project structure that is confusing on day one. Second, the data: assembling a model-ready terrain grid and rainfall grids by hand takes hours per event and is hard to reproduce. This module removes both obstacles. It walks you through the complete 2D rain-on-grid workflow on a real flood (Fort Atkinson, Iowa, August 2016), then shows you how to fetch the two essential inputs, a DEM and gridded rainfall, automatically from free open data services with a Python notebook (Hurricane Helene over the Swannanoa River valley, September 2024). It closes with RAS Commander, an open-source Python package that scripts HEC-RAS itself. Short description Learn what HEC-RAS 2D does and follow the workflow from digital elevation model to flood map: terrain, mesh, boundary conditions, gridded rainfall forcing, simulation, and results in RAS Mapper. Then learn to acquire model-ready inputs automatically from open data (USGS 3DEP elevation, NOAA MRMS radar rainfall, GOES satellite rainfall) in a Colab notebook, and see how the RAS Commander Python package automates model runs and GIS exports. You finish by drafting a defensible one-page model setup plan for a flood hazard mapping job. Audience Early-career forecasters and hydrometeorologists at National Meteorological and Hydrological Services who need flood inundation maps and want a realistic, low-cost path to producing them. No prior HEC-RAS experience is assumed. Estimated effort About 1 hour 45 minutes total (1.5 to 2 hour range). Self paced. Section Estimated time About page (read on enrolment) 5 min Section 1, Introduction 5 min Section 2, HEC-RAS 2D foundations (includes Learning Activity 1) 40 to 45 min Section 3, Automatic data access (includes Learning Activity 2) 30 to 35 min Section 4, Authentic task 15 to 20 min Prerequisites Basic hydrology vocabulary: rainfall intensity, hyetograph, hydrograph, runoff. Basic raster GIS concepts: what a DEM is, cell size, map projection. Python at run-the-notebook level for Learning Activity 2 (all code is provided). HEC-RAS itself runs on Windows. Installing it is optional: Learning Activity 1 offers a screenshot-based alternative track. What you will be able to do by the end Describe the capabilities of HEC-RAS and name the three working windows and what each one is for. Explain every step of the 2D rain-on-grid workflow: DEM to terrain, mesh with breaklines and refinement regions, boundary condition lines, gridded rainfall, run, and results. Justify a mesh cell size and computation interval for a stated flood mapping purpose. Acquire a model-ready DEM and 24 hours of rainfall grids for a named basin and event using free open data services and a Python notebook. Explain how HEC-DSS, Vortex, and RAS Commander fit around HEC-RAS in an automated workflow. Draft and defend a one-page 2D model setup plan that ends in depth and velocity GIS layers for a named user. Acknowledgments Module developed for the World Meteorological Organization (WMO) capacity building activity under the Early Warnings for All Initiative. The project is funded jointly by the "Early Warning System for Floods - United States Department of States (EWS-F US DoS)" and the "Supporting Regional Cooperation to Strengthen Operational Multi-Hazard Forecasting and Early Warning Systems at National Level in the South-West Indian Ocean (CREWS South-West Indian Ocean)" projects.