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 |
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1. Select storage type to be used at the site
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2. Determine the area of the site that will be drained to the OSD storage system
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3. Determine the amount of impervious and pervious areas draining to the OSD storage system Pre-development
Post-development
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| 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 Pre-Development flows, Qp | |
| Pre-Development
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 |
Pre-Development
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 Post-Development flows, Qa | |
| Post-Development1.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 |
Post-Development1.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 |
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6. Determine the required PSD for the site (Equation 19.1 with Equations 19.1c and 19.1d for below-ground storage) |
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7. Determine the required SSR for the site (Equation 19.2 with Equations 19.2c and 19.2d for below-ground storage) |
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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 | |
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