OSD Rational Method (MSMA 1)
 Project file MiTS 1(PondCAD) here
 Project file MiTS 2 here
 Software Report here
 Manual Excel Spreadsheet here
 Linear interpolator here
*kindly informed that you will need to download the manual excel spreadsheet and software report
Objective
 Comparison between software calculation and manual calculation. To ensure that the results are the same
 Software extract the correct value from Design Chart/Table in MSMA 1
Project Development details
Area: 0.687 ha
100 m of overland flow
520 m flow in an open drain
Catchment area average slope 1%
MSMA 1st Edition
OSD Sizing Procedure (MSMA 1 – Rational Method)  
Manual Excel Spreadsheet  MiTS Software 
1. Select storage type to be used at the site


2. Determine the area of the site that will be drained to the OSD storage system


3. Determine the amount of impervious and pervious areas draining to the OSD storage system Predevelopment
Postdevelopment


4. Determine the time of concentration, tc and tcs  
Refer design chart 14.1 Nomograph for Estimating Overland Sheet Flow Times, to
From Design Chart 14.1, tc = to + td = 10 min 
In MiTS softwareUsing Time of Concentration for Natural Catchment Equation 14.6
Calculated from Equation 14.6, tc = 10 min 
5(i). Calculate the PreDevelopment flows, Qp  
PreDevelopment
1. Calculate rainfall depth,P30 and P60 using Equation 13.2 2. Determine FD from Table 13.3 3. Calculate Rainfall Intensity using Equations 13.3 & 13.4 4. Calculate Qp = CIA P30 = 48.091 mm, P60 = 62.045 mm Pd = 32.32 mm Hence, I = Pd/tc = 32.32 / (10/60) =193.94 mm/hr Qp = CIA = 0.230 m3/s 
PreDevelopment
1. Calculate rainfall depth,P30 and P60 using Equation 13.2 2. Determine FD from Table 13.3 3. Calculate Rainfall Intensity using Equations 13.3 & 13.4 4. Calculate Qp = CIA P30 = 48.09 mm, P60 = 62.05 mm Pd = 32.32 mm Hence, I = Pd/tc = 32.32 / (10/60) =193.94 mm/hr Qp = CIA = 0.230 m3/s 
5(ii). Calculate the PostDevelopment flows, Qa  
PostDevelopment1.Calculate rainfall depth,P30 and P60 using Equation 13.2
2. Determine FD from Table 13.3 3. Calculate Rainfall Intensity using Equations 13.3 & 13.4 4. Calculate Qp = CIA P30 = 48.091 mm, P60 = 62.045 mm Pd = 38.04 mm Take tc as nearest = 15 min Hence, I = Pd/tc = 38.04 / (15/60) =152.18 mm/hr Qa = CIA = 0.231 m3/s 
PostDevelopment1.Calculate rainfall depth,P30 and P60 using Equation 13.2
2. Determine FD from Table 13.3 3. Calculate Rainfall Intensity using Equations 13.3 & 13.4 4. Calculate Qp = CIA P30 = 48.09 mm, P60 = 62.05 mm Pd = 38.04 mm Hence, I = Pd/tc = 38.04 / (15/60) =152.18 mm/hr Qa = CIA = 0.230 m3/s 
6. Determine the required PSD for the site (Equation 19.1 with Equations 19.1c and 19.1d for belowground storage) 

7. Determine the required SSR for the site (Equation 19.2 with Equations 19.2c and 19.2d for belowground storage) 

Therefore, the required SSR (with 20% added for safety factors) = 157.392 m3 
Therefore, the required SSR (with 20% added for safety factors) = 161.075 m3 
8. Determine storage Dimensions  