HEC-RAS Online River Hydraulics & Flood Simulation
Run HEC-RAS river simulations online. 1D and 2D flood modeling, floodplain management, and cloud-scale engine execution.
What is HEC-RAS and how does it work?
HEC-RAS (Hydrologic Engineering Center's River Analysis System) is the definitive river hydraulics modeling software for civil engineering practice. It is widely used worldwide for flood insurance studies, dam safety evaluations, and bridge/culvert design.
The system performs one-dimensional steady and unsteady flow calculations, two-dimensional unsteady flow modeling, combined 1D/2D hydrodynamic simulation, sediment transport and mobile bed computations, and water temperature and water quality modeling.
Run HEC-RAS in your browser (no installation required)
HEC-RAS traditionally demands significant desktop resources and Windows-only installation. HydroBOA eliminates these constraints by running the engine on scalable cloud infrastructure. Manage river models from any device — edit cross-sections, define flow data, configure 2D mesh areas, and execute unsteady simulations directly from your browser or mobile device.
1D/2D Flow
Terrain & Mesh
Regulatory Ready
1D and 2D flood modeling cloud workflows
Handle complex 2D mesh generation, terrain processing, and multi-day unsteady flow simulations without taxing local hardware. HydroBOA's cloud infrastructure scales dynamically for large-scale dam breach analyses, regional flood studies, and coupled 1D/2D models that would overwhelm a typical workstation.
Results are delivered as interactive flood maps with depth grids, velocity vectors, and water surface elevation profiles. Export to GIS-ready formats or generate regulatory-grade PDF reports directly from the platform.
Cloud vs Desktop HEC-RAS: Result Fidelity
When you run a model in HydroBOA's cloud instead of HEC-RAS on your Windows desktop, do you get the same answer? Short answer: yes — to engineering tolerance, across every regime we have tested. Mass conservation, water-surface elevations, flows, and structure ratings match a native Windows HEC-RAS run.
- On 1D models controlled by hydraulic structures (bridges, culverts, hydraulic jumps, levee overtopping), cloud and desktop water-surface profiles are bit-for-bit identical — zero difference.
- On 2D models, mass balance and water-surface elevations are effectively identical; the only differences are sub-inch, confined to a handful of cells at wet/dry edges and high-velocity zones, and they fall within HEC-RAS's own run-to-run sensitivity.
- On a pump + storm-sewer model, cloud and desktop reproduce the same event — same surcharge timing, same pump on/off cycle, same peak water levels — differing only by a fraction of a foot in the transient at a few pump-controlled nodes.
- On water-quality models — temperature and multi-constituent nutrient (NSM) chemistry, including reversing tidal flow — cloud and desktop are bit-for-bit identical, with zero difference across every constituent.
| Regime | Cloud vs Desktop |
|---|---|
| 1D steady — bridges / culverts / hydraulic jumps / levees | Bit-for-bit identical — 0.000 ft, 0.000 cfs at every cross-section |
| 1D steady-flow profiles (culverts / structures) | Bit-for-bit identical — 0 of 17,612 result cells differ |
| 1D unsteady dam breach (Bald Eagle “Sunny Day Failure”) | Bit-for-bit identical — 0 of 4,303,803 result cells differ (full 24-hr breach) |
| 1D steady ice-covered river (Thames ice cover / jam) | Bit-for-bit identical — 0 of 31,493 cells differ — incl. ice-affected bed shear stress |
| 2D wetting / drying (worst cell) | Machine precision — ≈ 1×10⁻¹³ ft |
| Coupled 1D/2D — 2D water surface | ≤ 2.3 mm — (~0.008 ft) |
| 2D mass-balance (volume) error | ≈ 1 part in 10,000 — Δ ≈ 5×10⁻⁷ percentage-points |
| 2D water surface (representative model) | Sub-inch — 0 of 5,765 cells differ by > 0.1 ft |
| Pump / pipe storm sewer | Same event — timing, surcharge, peaks identical; transient ≤ 0.49 ft at 7 of 133 nodes |
| Quasi-unsteady sediment transport | Bit-for-bit identical — 0 of 217,692 result cells differ |
| 1D unsteady sediment transport | Bit-for-bit identical — 0 of 34,027,092 result cells differ |
| 2D unsteady sediment transport | Water surface identical — 0 of 371,833 cells differ meaningfully (max ≈ 6×10⁻⁵ inch); 0.0000% volume error |
| 2D debris / mud flow (non-Newtonian Bingham) — Parsons flume, Gibson et al. (2020) | Water surface bit-for-bit identical — max|Δ| = 0 with computed geometry; value-exact (≤ 2.4×10⁻⁷ ft) rebuilt from the raw model |
| 1D water quality — temperature + nutrient (NSM) constituents | Bit-for-bit identical — max|Δ| = 0 vs desktop on every constituent and thermal dataset (10 validated models, prepared and raw) |
| Tidal / reversing-flow water quality (multi-constituent) | Bit-for-bit identical — 8 constituents over a 14-day reversing tidal cycle — 0 difference vs desktop |
| 2D inundation maps (max water-surface raster) | Sub-inch — mean Δ 1.4×10⁻⁶ ft; 0 of 6,146 cells differ by > 0.01 ft |
| 2D rendered stored-map tiles (depth / WSE / velocity GeoTIFFs) | Pixel-for-pixel identical — 0 of 35,813,896 pixels differ on each map (max|Δ| = 0) |
| Engine point-release drift (maintenance updates) | Zero change — on every model |
The benchmark — HEC-RAS's own tolerance
HEC-RAS documentation classifies up to 1–3 ft of water-surface-elevation difference between identical 2D runs — explicitly “on the same or different computers” — as “hydraulically reproducible” (not significant for hydraulic studies). Every cloud-vs-desktop difference above sits far inside that published envelope: the largest single-cell difference on the representative 2D model is about a quarter inch (~0.02 ft) — roughly 50–150× smaller than HEC's range. Deterministic regimes — 1D steady, unsteady, structures, and sediment — match bit-for-bit; 2D and coupled regimes match well within HEC-RAS's own reproducibility envelope.
“Generally, HEC-RAS 2D simulations which are numerically stable are hydraulically reproducible, meaning that the results may vary between identical runs on the same or different computers within a small range that is not significant for hydraulic studies (e.g. < 1-3 ft water surface elevation difference).”
What we measured — a representative 2D model
A 2D unsteady Muncie model (5,765 cells, 22,328 faces, an unsteady flood event), run in the cloud and on native Windows HEC-RAS from identical inputs, compared cell-by-cell.
| Quantity | Cloud | Desktop (Windows) |
|---|---|---|
| Volume conservation (mass-balance error) | 0.0019261 % | 0.0019259 % |
| Starting volume | identical | identical |
| Solver iteration counts | identical (bit-for-bit) | identical (bit-for-bit) |
- Water surface: mean difference 0.00006 ft (about six ten-thousandths of an inch); largest difference ≈ a quarter inch. 5,751 of 5,765 cells agree within 0.01 ft; zero cells differ by more than 0.1 ft.
- Velocity: mean difference 0.0002 ft/s; 18 of 22,328 faces differ by more than 0.1 ft/s, clustered in one high-velocity zone.
Sediment transport (mobile-bed) — both input modes
Mobile-bed sediment transport is the most demanding HEC-RAS regime. Each regime was validated two ways — from a raw model and from an already-prepared model — each compared cell-by-cell to a native Windows desktop run.
| Regime | From a raw model | From a prepared model |
|---|---|---|
| 1D unsteady sediment | Bit-for-bit identical — 0 / 34,027,092 cells | Bit-for-bit identical |
| 2D unsteady sediment | Water surface identical — 0 / 371,833 cells (max ≈ 6×10⁻⁵ in); 0.0000% volume error | Sub-noise-floor — 4 / 371,833 cells |
| Quasi-unsteady sediment | Bit-for-bit identical — 0 / 217,692 cells | Bit-for-bit identical |
Decision-grade flood & hazard products
Clients sign off on the map, not the cells. On the mobile-bed sediment model and on a 2D flood model, every decision-grade product is identical cloud-vs-desktop:
- Inundation extent — wet/dry concordance 100%, extent IoU 1.000, inundated-area difference 0.0% (at 0.1 / 0.5 / 1.0 ft thresholds).
- Depth grids — band concordance 100%; 100% of cells, core and wet/dry-fringe, agree within 0.1 ft.
- Hazard zones — class concordance 100% under all four frameworks (D·V, FEMA depth, Australian AR&R 2019 H1–H6, UK FD2320) — zero gross misclassifications.
- Impact footprint — footprint IoU 1.000, affected-area difference 0.0%.
Water quality — validated, cloud = desktop
Water-quality modeling is live in the cloud on the genuine HEC-RAS engine: water temperature (full energy budget and equilibrium temperature), the multi-constituent Nutrient Simulation Module (algae, ammonium, nitrate, organic nitrogen, organic and inorganic phosphorus, and dissolved oxygen), general constituents, solids, mass injection, and multi-module coupling. Across every water-quality model we have validated — including junction networks and multi-constituent tidal runs with genuine flow reversal over a 14-day cycle — cloud results are bit-for-bit identical to a native Windows HEC-RAS run (max|Δ| = 0 on every constituent and thermal dataset), whether the model arrives already prepared or is built from a raw model in the cloud.
Why use HydroBOA for HEC-RAS modeling?
HydroBOA combines the HEC-RAS engine with cloud scalability, automated GIS-based terrain processing, and version control built for teams working on high-stakes flood-compliance projects. Unlike standalone desktop HEC-RAS, HydroBOA lets your team collaborate on river models in real time, with full audit trails and cross-platform access from Windows, macOS, Linux, iOS, and Android.
HEC-RAS Use Cases
Floodplain management and mapping
Dam breach analysis and impact assessment
River restoration and hydraulic design projects
Frequently Asked Questions
Is there a HEC-RAS app?
Yes. HydroBOA is a HEC-RAS app you can use on any device. It runs the genuine, unmodified USACE HEC-RAS engine in the cloud and installs as a Progressive Web App on Windows, macOS, ChromeOS, iOS, and Android, so it works like a native HEC-RAS application for 1D and 2D river hydraulics and flood modeling — with no download, admin rights, or app-store approval required.
What is a good browser-based or online HEC-RAS app?
HydroBOA is a browser-based HEC-RAS app that runs the real USACE HEC-RAS engine rather than an approximation, so 1D and 2D results are consistent with desktop HEC-RAS. It runs on any device with no installation and adds integrated GIS, terrain handling, and Git-style version control.
Does HydroBOA produce the same results as desktop HEC-RAS?
Yes. HydroBOA runs the genuine, unmodified USACE HEC-RAS engine in the cloud — the same computational engine as desktop HEC-RAS, not a re-implementation. One-dimensional steady and unsteady flow results match desktop HEC-RAS, and two-dimensional unsteady results match desktop HEC-RAS according to HEC-RAS's own documented numerical methods.
Is HEC-RAS 2D modeling accurate and identical to the desktop in HydroBOA?
Yes. HydroBOA's 2D mesh computations run on the genuine HEC-RAS engine and follow HEC-RAS's own documented 2D solver behavior, so depth grids, velocities, and water-surface elevations are consistent with desktop HEC-RAS for the same model and terrain.
Is HydroBOA's online HEC-RAS the real engine or an approximation?
It is the real, official USACE HEC-RAS engine running in the cloud, not an approximation or re-implementation. Results are validation-grade and reproducible against desktop HEC-RAS.