In the Stormwater module, users can choose the analysis type of their project to be analysed whether by “Design’ or ‘Analysis’.
What is StormWater Design? #
If the users choose by Design, the project will be analysed as a preliminary design based on the design standard, where it is the iteration of drain sizes and IL (if iterate == Yes). This design is based on a simple, static manning equation and doesn’t involve routing, ie: it doesn’t recognize time-varying inputs, and will always give a constant output for velocity, flow, water depth and so on.
What is StormWater Analysis? #
If the users choose the Analysis, the project will be analysed as per the EPASWMM, which means that the drain and storage system will be analysed for the computation flow, discharge, velocity, water depth and so on according to the EPASWMM engine.
When is Analysis results should be matched with the Design? #
We should expect that Analysis results should be the same with Design, when the following conditions are met:
- The inflow is static, meaning the inflow is the same throughout the time
- Analysis result is using ‘SteadyWave’, which is just manning equation analysis with static analysis
- We don’t consider the capacity of a storage node, just drains
- The flow inside the drain is not closed to full flow, because the manning equation that the Design uses is only applicable for non-full flow situation, and EPASWMM SteadyWave can use a different, more exact calculation for near full flow situation
The table below shows the results from both design and analysis
Example #
Provide here is the example project file
| Analysis Type: Design |
 |
| Anaysis Type: Analysis |
 |
Velocity #
| Analysis Type | Drain Mark | Max. Water Depth Velocity (m/s) | Velocity (m/s) |
| Design | 1 | 1.23 | – |
| 2 | 1.23 | – | |
| Analysis | 1 | – | 1.23 |
| 2 | – | 1.23 |
Flow #
| Analysis Type | Drain Mark | Peak Flow (m3/s) | Max Flow (m3/s) |
| Design | 1 | 0.13 | – |
| 2 | 0.13 | – | |
| Analysis | 1 | – | 0.13 |
| 2 | – | 0.13 |
Water Depth #
| Analysis Type | Drain Mark | Max. Water Depth (m) | Max. Water Depth (m) |
| Design | 1 | 0.17 | – |
| 2 | 0.17 | – | |
| Analysis | 1 | – | 0.17 |
| 2 | – | 0.17 |
Conclusion #
In conclusion, the results obtained from both analysis types have the same value although the engine is different. For both analysis types, the maximum velocity is 1.23 m/s, the maximum flow is 0.13 m3/s and the maximum depth is 0.17 m.
This gives us confidence that both types of analysis yield correct results.
