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Designing On-site Detention

OSD – Simplified Method #

Click Add in Project View to create a new MSMA project. Choose OSD, select MSMA 2nd Edition, create the name of the project, select the method to be used and click Create. Method used in section 2.1 is Simplified Method.

Click the dropdown list to choose the storage type which is either Above Ground or Below Ground. 

Pond Requirement #

  1. Select the location in the list.
  1. Input Area(ha) , Impervious and Pervious area.
  1. Select Terrain based on surface slope. 
  1. Click on the Calculate button to obtain PSD and SSR value.

Pond Sizing #

Click on the Pond Sizing tab to proceed on pond sizing design. 

  1. Select the type of the pond (rectangular ,circular or irregular).
  1. Input the dimension of the pond type such as length, width, and depth to calculate the volume.
  1. Click the “ Calculate” button to obtain the Depth of Water and Volume.

Note: Warning message will pop out if the designed volume is less than the required storage.

Outlet Design #

Click on Outlet Design for outlet design. 

1) Inlet Pipe

a. Input diameter and number of orifice. 

2) Primary Outlet

a. Input Height from bottom of Pond to bottom of orifice, H. Effective head, Ho will be calculated.

b. Input diameter and number of orifice.

3) Secondary Outlet

a. Select Outlet Type  (only for above ground OSD)

b. Input diameter and number of orifice (or weir dimensions, only for above ground OSD)

Click Analyse to generate the result. 

Result #

Click Textual Report, Summary Report, Detailing, or Appendix tabs to show the result respectively.

OSD – Swinburne Method #

Click Add in Project View to create a new MSMA project. Choose OSD, select MSMA 2nd Edition, create the name of the project, select the method to be used and click Create. Method used this section is Swinburne Method.

Select the type of the OSD by clicking the drop down list.

OSD design can also be integrated from drainage if the analysis of drainage has been carried out. 

Pre-development #

Calculate pre-development discharge by inputting data in Pre tab.

  1. Input or select location. The location can be input by entering the location of Longitude and Latitude. Click the “Use” button to use the proposed nearest rain gauge location. The Location also can be selected by clicking on the Raingauge Location drop list.

  1. The fitting constants are generated automatically and it is editable. Click on button to change the fitting constants to default value based on selected location.

  1. Input the length of flow path from catchment divide to outlet, slope of stream flow path and catchment area to obtain tc and it is editable.

  1. Input the “Impervious”  and “Pervious”  area for Pre-development.

  1. Select ARI. Rainfall Intensity is generated automatically and it is editable.

  1. Select land use or soil type by clicking button. Select the land use or soil type in the popped out Runoff Coefficient Table by clicking the value in the table.
  1. Click Calculate to generate pre development discharge.

Post-development #

Calculate post-development discharge by inputting data in the Post tab.

  1. Input overland flow length, slope of overland surface and manning coefficient to obtain to.

  1. Input drain flow length and average velocity to obtain td and  tc.

  1. Input “Impervious”  and “Pervious”  area for post development.

  1. Select ARI. The fitting coefficient and rainfall intensity are generated automatically and editable.

  1. Select land use or soil type by clicking button. Select the land use or soil type in the popped out Runoff Coefficient Table by clicking the value in the table.

6. Click the “ Calculate” button to obtain post-development discharge.

Pond Storage #

Determine required storage by inputting data in the Pond Storage tab.

  1. Input tcs to generate the SSR.

  1. Click the “ Calculate” button to obtain the Required SSR. Make sure maximum SSR does not fall at the last row as the value may not be the maximum value. Change the number of rows from Options > Project Parameters > Det. Facility > OSD > No. of Range 

Pond Sizing #

Design pond volume by inputting data in the Pond Sizing tab. The pond sizing design can be synchronized from the pond platform. Pond platform can be assigned in EW modules (Platform > Spread Input > Type Column > Assign the platform as Pond)

  1. Select the type of the pond

  1. Input length, width, and depth to calculate the volume. (Above ground with side slope)

  1. Click the “ Calculate” button to obtain the Depth of Water and Volume.

Note: Warning message will pop out if the designed volume is less than the required storage.

Outlet Design #

Design outlet by inputting data in Outlet Design tab.

  1. Primary Outlet

a. Input Height from bottom of Pond to bottom of orifice, H. Effective head, Ho will be calculated.

b. Input diameter and number of orifice.

      2. Secondary Outlet

a. Select ARI.

b. Input the Broad-crested Weir Coefficient, CBCW.

c. Input the effective head and weir width.

Result #

Click the “ Analyse” button to generate textual report, summary report, pond detailing, and graph.

Click Textual Report, Summary Report, Detailing, or Graph tabs to show the outcomes respectively.

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