Benchmark for Rational Detention Pond Method– MSMA 2 Appendix 7A

Objective:  #

To benchmark MES results with MSMA 2 detention pond rational method  (Chapter 7 Appendix A)

Sample MiTS 2 Project file here 

Manual Spreadsheet here

MSMA 2nd Edition here 

Pre Development  #

User may refer to “How to Estimate Time of Concentration.” blog post for further reference

• Tc and Rainfall Intensity 

For benchmarking purposes, we will override the Tc value in MiTS 2 by following MSMA 2 values. 

• Peak flow for Qpre

Post Development #

• Ditto as per in pre development for tc

• Preliminary Estimate Pond Volume

User may refer to “Preliminary Pond Volume of A Pond” to know more about this

• Peak flow for Qpost

Pond Sizing #

• Follow MSMA 2 pond area

• Comparing Stage-Storage Relationship between MiTS 2 and MSMA 2

How to compute the stage-storage relationship & stage-discharge relationship #

Stage-Storage Relationship and Stage Discharge Relation and Storage Indicator Numbers here

Outlet Design #

• At this stage, for the reason that will become clear later, we are comparing the results of our software against the MSMA 2 manual example and also our own spreadsheet.

How ‘Pond Routing’ works #

Pond Routing here

Minor routing 1st trial  Orifice size propose in MSMA 2 for 1st trial is 2m x 1m  Hence if we use this value in our manual spreadsheet and MiTS 2, and then compared with MSMA 2, the values agreed.

Minor routing 2nd trial  Orifice size propose in MSMA 2 for 2nd trial is 0.5m x 0.5m  However, at this stage when a comparison is done with manual spreadsheet and MiTS 2, values between manual spreadsheet and MiTS 2 are the same but different when compared to MSMA 2. It appears that there is some self-inconsistency when it comes to the 1st and 2nd trial for MSMA 2 manual example. Thus we will compare only between the MiTS 2 and manual spreadsheet from this point onwards.

So we will only be benchmarking MiTS 2 with MSMA 2 up till ‘Preliminary Estimate Pond Value’ and starting at orifice routing (for minor, major and secondary), we will start to benchmarking with our Manual Spreadsheet. 

At this stage we compared the Stage Discharge table and pond routing for each stage

Minor Storm Outlet design

i) Stage Discharge table ii) for pool routing can refer to manual spreadsheet and pool routing in MiTS 2 at outlet design > display minor results

Major Storm Outlet design

i) Stage Discharge table ii) for pool routing can refer to manual spreadsheet and pool routing in MiTS 2 at outlet design > display major results

Secondary Outlet design

i) Stage Discharge table ii) for pool routing can refer to manual spreadsheet and pool routing in MiTS 2 at outlet design > display secondary results

Conclusion  #

As a conclusion, the results from MSMA 2 shown is accurate. The discrepancy between MSMA 2, MiTS 2 software and Manual Spreadsheet is small which is less than 5%. Hence, it can be said that our MiTS 2 results is accurate as per MSMA 2 results.