Extracting Stage–Discharge Relationships for Design Studies

Developing accurate stage–discharge relationships (rating curves) is essential in hydraulic design and flood analysis. These relationships describe how water surface elevation (stage) varies with flow (discharge) at a specific cross section or location. Traditionally, these are derived from field measurements, but in the Surface-water Modeling System (SMS), you can generate them directly from numerical model results.

Using built-in tools, SMS allows you to extract, plot, and analyze stage–discharge data from your SRH-2D or other 2D hydraulic simulations—no external software required.

Why Use SMS to Generate Rating Curves?

By creating rating curves from simulated results, you can:

• Evaluate hydraulic performance under design flow conditions

• Assess changes due to structures, channel modifications, or floodplain development

• Reduce uncertainty by analyzing results from multiple flow scenarios

This approach is especially powerful when physical data are limited or when assessing hypothetical design conditions.

Step 1: Define Monitoring Locations

Before running the model, define monitoring points or cross sections using the Observation Coverage in the Map module. Place these points at locations where you need a stage–discharge curve—such as upstream and downstream of a bridge or control structure.

Step 2: Run Multiple Flow Simulations

SMS allows you to create multiple simulations in the same project. To establish a curve, you’ll need results from simulations with different discharges. For example, run several SRH-2D simulations with varied inflow hydrographs or steady-state flow rates.

Step 3: Extract Results in SMS

Once all simulations are complete:

1. Load your simulation results into SMS.

2. Select the Observation Profile Tool or the Data Calculator to extract stage (water surface elevation) and discharge (flow rate) values at your monitoring points.

3. Use the Plot Wizard to create an XY Series Plot with discharge on the x-axis and water surface elevation on the y-axis.

SMS automatically generates smooth rating curves from your dataset.

Step 4: Analyze and Export

Refine your plot using the Plot Options dialog. You can export results as a CSV file for documentation or import into hydraulic design tools. Comparing curves between different simulations helps visualize how design changes affect flow capacity.

Conclusion

Extracting stage–discharge relationships in SMS provides engineers with a powerful, model-based way to evaluate hydraulic conditions and support design decisions. By leveraging observation points, multiple simulations, and built-in plotting tools, SMS streamlines the entire process—from model to rating curve—within one workspace. Download SMS and gather stage-discharge relationships for your projects today!