This article documents the Storm Sync Proportional Loss comparison with the legacy PondCAD MSMA2 Time Area module. This article focuses on comparing the calculated catchment hydrographs from both modules to check whether Storm Sync produces consistent results with the legacy PondCAD module.
For instructions on setting up Storm Sync Time Area analysis and reviewing the output result, refer to the Storm Sync Time Area hydrology guide and Storm Sync Time Area Results guide.
The sample projects used for this comparison are:
Reference case and Storm Sync setup #
The PondCAD benchmark project uses the Pond MSMA 2 Time Area module with the following analysis settings:
| Parameter | Configuration |
|---|---|
| Development condition | PostDev |
| Design event | Major (50-year ARI) |
| Rainfall duration | 15 mins, 30 mins and 180 mins |
| Catchment area | 10 ha (100% pervious) |
| Time of concentration (Tc) | 15 minutes |
| Time Area bands | Three bands, each with a 5-minute isochrone band |
| Rainfall data | Temporal pattern from MSMA2 Appendix 2.C (Region 2) |
For the Storm Sync benchmark, the same catchment characteristics and rainfall data are configured in the Time Area method. Proportional loss model is selected to calculate the rainfall losses, and the resulting inflow hydrograph is compared against the inflow hydrograph obtained from the PondCAD calculation.
Inflow hydrograph comparison #
PondCAD timestamps each hydrograph ordinate at the end of the corresponding rainfall interval, whereas Storm Sync timestamps the same physical flow rate at the start of its output interval. To align the hydrographs for comparison, add 5 minutes to each Storm Sync timestamp before pairing the corresponding flow values.
All paired flow values match within a tolerance of 0.0001 – 0.0005 m³/s.
Storm duration: 15mins
| PondCAD time (min) | Storm Sync time (min) | PondCAD Inflow (m³/s) | Storm Sync Inflow (m³/s) | Difference |
|---|---|---|---|---|
| 5 | 0 | 0.481 | 0.480 | 0.001 |
| 10 | 5 | 2.501 | 2.497 | 0.004 |
| 15 | 10 | 4.488 | 4.483 | 0.005 |
| 20 | 15 | 4.007 | 4.003 | 0.004 |
| 25 | 20 | 1.988 | 1.986 | 0.002 |
| 30 | 25 | 0.000 | 0.000 | 0.000 |
Storm duration: 30mins
| PondCAD time (min) | Storm Sync time (min) | PondCAD Inflow (m³/s) | Storm Sync Inflow (m³/s) | Difference |
|---|---|---|---|---|
| 5 | 0 | 0.000 | 0.000 | 0.000 |
| 10 | 5 | 0.927 | 0.927 | 0.000 |
| 15 | 10 | 3.536 | 3.536 | 0.000 |
| 20 | 15 | 4.622 | 4.622 | 0.000 |
| 25 | 20 | 4.596 | 4.596 | 0.000 |
| 30 | 25 | 2.723 | 2.723 | 0.000 |
| 35 | 30 | 1.637 | 1.637 | 0.000 |
| 40 | 35 | 0.736 | 0.736 | 0.000 |
| 45 | 40 | 0.000 | 0.000 | 0.000 |
Storm duration: 180mins
| PondCAD time (min) | Storm Sync time (min) | PondCAD Inflow (m³/s) | Storm Sync Inflow (m³/s) | Difference |
|---|---|---|---|---|
| 15 | 10 | 0.000 | 0.000 | 0.000 |
| 30 | 25 | 0.524 | 0.525 | 0.001 |
| 45 | 40 | 0.781 | 0.781 | 0.000 |
| 60 | 55 | 0.991 | 0.992 | 0.001 |
| 75 | 70 | 1.586 | 1.588 | 0.002 |
| 90 | 85 | 1.871 | 1.873 | 0.002 |
| 105 | 100 | 1.599 | 1.600 | 0.001 |
| 120 | 115 | 1.202 | 1.203 | 0.001 |
| 135 | 130 | 0.979 | 0.980 | 0.001 |
| 150 | 145 | 0.768 | 0.769 | 0.001 |
| 165 | 160 | 0.669 | 0.670 | 0.001 |
| 180 | 175 | 0.520 | 0.521 | 0.001 |
| 195 | 190 | 0.000 | 0.000 | 0.000 |
The corresponding peak times in PondCAD and Storm Sync differ by 5 minutes due to their timestamp conventions. This five-minute offset does not represent a difference in the calculated peak flows.
| Module | Time Area Inflow at Storm Duration 180 mins |
|---|---|
| Storm Sync |  |
| Legacy PondCAD |  |
What this comparison establishes #
Overall, the benchmark demonstrates calculation parity between PondCAD and Storm Sync for the legacy proportional-loss method under the specified rainfall pattern, storm duration, and fully pervious catchment configuration. The findings apply only to the specified model configuration and should not be taken as a general indication of parity under other modelling conditions.
For the Storm Sync result displays, see the Storm Sync Time Area Results guide. The original PondCAD MSMA2 detention-pond article describes the legacy module’s broader setup.
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