Rainfall Runoff Modeling with HEC-HMS and HEC-RAS

RAS Mapper as a GIS Tool for Terrain and Spatial Preparation

Preparing terrain and watershed data for hydrologic and hydraulic workflows

·       Terrain, projection, imagery, land cover, soils, stream networks, and gage datasets

·       Using RAS Mapper to organize, visualize, and prepare spatial inputs

·       Terrain processing concepts for HEC-RAS and HEC-HMS applications

·       Data quality, resolution, watershed boundaries, and coordinate system considerations

·       Workshop setup and overview of comparison datasets

Setting Up a Basin Model in HEC-HMS

Building the watershed representation

·       HEC-HMS project organization and basin model components

·       Subbasins, reaches, junctions, reservoirs, diversions, sources, sinks, and outlets

·       Parameterizing drainage areas, slopes, lengths, connectivity, and routing elements

·       Importing or entering physical basin data

·       Hands-on basin model setup exercise

Applying Meteorological Models in HEC-HMS

Translating precipitation data into model inputs

·       Meteorological model types and precipitation data sources

·       Design storms, frequency storms, observed events, gridded precipitation, and gage weighting

·       Temporal distribution, time step selection, and missing data considerations

·       Linking meteorologic models to basin models and control specifications

·       Reviewing precipitation inputs and storm event assumptions

Transform, Loss, and Routing Methods in HEC-HMS

Selecting methods that fit the watershed and data

·       Loss methods such as SCS Curve Number, Green-Ampt, deficit and constant, and initial and constant approaches

·       Transform methods such as SCS Unit Hydrograph, Clark Unit Hydrograph, ModClark, and Snyder

·       Baseflow and channel routing method options

·       Parameter estimation, sensitivity, and model limitations

·       Running HEC-HMS simulations and reviewing hydrographs

Direct Precipitation and HEC-RAS Rain-on-Grid Modeling

Applying rainfall directly to 2D hydraulic models

·       Conceptual differences between HEC-HMS hydrograph routing and HEC-RAS rain-on-grid modeling

·       Applying precipitation to 2D flow areas

·       Terrain, mesh, roughness, infiltration, and time step implications

·       Boundary conditions, initial conditions, and model stability considerations

·       Running rain-on-grid simulations and interpreting spatial results

Comparing and Calibrating HEC-HMS and HEC-RAS Results

Using observed data to evaluate and refine model performance

·       Comparing hydrographs, peak flow, runoff volume, timing, depths, and inundation patterns

·       Calibration with stream gage, precipitation, high water mark, and observed event data

·       Sensitivity analysis for loss, transform, routing, roughness, infiltration, and mesh assumptions

·       Communicating uncertainty and documenting modeling decisions

·       Final comparison exercise, questions and answers, and wrap-up