To get a matching result between the Stormwater module and detention pond in the MSMA module, the project’s default setting/design must be similar. Several conditions must be met for the results to match:

1) Both the Stormwater module and MSMA module must include/not include the CCF factor. To adjust this CCF factor, go to;

• StormWater: Options > Project Settings >  Storm Design > Design Guideline > Malaysia > CCF Inclusion
• MSMA: Options > Project Parameters > Det. Facility > IDF > Design > Include CCF

2) Verify that both modules calculate for the same design ARI

• StormWater: Options > Project Settings > Storm Design > Routing > Analysis Events

• MSMA: Choose design ARI during designing detention pond in; Pre > Stormwater Quantity Design Criteria

3) In the StormWater module, analyze as ‘Analysis’, not as ‘Design’

4) For the detention pond in the MSMA module, use the Rational Method when creating the project and use the constant weir coefficient method;

• Options > Project parameters > Det. Facility > Pond > Design > Weir coefficient method == Constant > Weir coefficient == 1.70

5) Verify that both modules have similar default settings for analysis [Routing Method, Tc, Num. of Storm Durations, Storm duration trial increments, routing steps, storage slice]

• StormWater: After finish designing, go to; Input > Project > Analyse > Inflow Source == CatchmentHydrology > Analysis Type == Analysis

• MSMA: Options > Project Parameters > Det. Facility > Pond > Design
  • For t_c, fix the value during designing Post development requirement

6) Verify that both pond and outlet dimensions have similar value

• StormWater;
  • Pond: Node & Storage > Spread Input > Node ‘x’ > Node & Storage Setting > Simple pond

• Stormwater;
  • Outlet: Drain > Spread Input > Drain ‘x’ > Link Type

• MSMA;
  • Pond: During the designing process in the ‘Pond Sizing’ tab

• MSMA;
  • Outlet: During the designing process in the ‘Outlet Design’ tab

Example #

StormWater module Project File

MSMA module Project File

Inflow Hydrograph #

The inflow hydrograph generated for each storm duration is different between the two modules except for the storm duration of 45 minutes. For each storm duration, the MSMA module shows similar peak flow while the StormWater module shows different peak flow values. These differences occur because;

1. In the MSMA module, the peak flow for each storm duration was based on the Post-development preliminary critical storm duration which is at minute 45, while 
2. In the StormWater module, it calculates each storm duration’s peak flow

Below is an example of 100 years ARI, refer to the orange line for the MSMA inflow hydrograph.

Storm Duration: 45 minute

MSMA Module ARI 2 – RED; ARI 50 – PURPLE; ARI 100 – ORANGE

StormWater – ARI: 2 Years

StormWater – ARI: 50 Years

StormWater – ARI: 100 Years

Inflow and Outflow Hydrograph #

In the MSMA module, only one inflow and outflow hydrograph was generated for each design ARI and it is based on critical storm duration. However, in the StormWater module, the inflow and outflow hydrograph for all storm durations were generated for each design ARI. 

Below is an example of the result for the inflow and outflow hydrograph during each critical storm duration.

2 Years ARI: 75 minute

StormWater module

MSMA Module

50 Years ARI: 60 minute

StormWater module

MSMA Module

100 Years ARI: 60 minute

StormWater module

MSMA Module

Stage-Storage Relationship Graph #

Both modules produce similar stage-storage relationship graphs.

StormWater module

MSMA Module

Conclusion #

In conclusion, the outcomes derived from both modules are the same despite the use of different engines. Both modules exhibit similar critical storm durations for each design ARI, as well as a similar stage-storage relationship graph.

This provides us with an assurance that the StormWater module generates accurate results.