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Designing On-site Detention

OSD #

Click Add in Project View to create a new MSMA project. Choose OSD, select MSMA 1st Edition, create the name of the project and click Create. 

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

Pre-development #

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

  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 land use or soil type by clicking button. Choose Urban or Rural. Select the land use or soil type in the popped out Runoff Coefficient Chart by clicking the box number.
  1. Select ARI and location.2P24and FD are generated automatically. Both are editable when tc less than 30 minutes.
  1. Click the “ Calculate” button to obtain pre-development discharge. Type of land use, fitting coefficients, runoff coefficient and intensity will be shown.

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 tp.
  1. Input “Impervious”  and “Pervious”  area for post development.
  1. Select land use or type soil by clicking button. Choose Urban or Rural. Select the land use or type soil in the popped out Runoff Coefficient Chart by clicking the box number.
  1. tc is calculated and editable.
  1. Select ARI.
  1. Click the “ Calculate” button to obtain post-development discharge. Type of land use, fitting coefficients, runoff coefficient and intensity will be shown.

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 > Design > No. of Range.

Pond Sizing #

Design pond volume by inputting data in the Pond Sizing tab.

  1. Select the type of the pond.
  1. Input the dimension of the pond design in order to calculate the volume.
  1. Click the “ Calculate” button to obtain the Required Depth of Water and Provided Storage 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. 

  1. 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 the result.  

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

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