Comparison of OSD results between software calculation and excel spreadsheet using ‘Swinburne Method’

OSD Swinburne Method (MSMA 1)  

1. Project file MiTS 2 here
2. Software Report here
3. Manual Excel Spreadsheet here
4. Linear interpolator here

*kindly informed that you will need to download the manual excel spreadsheet and software report

Objective #

1. Comparison between software calculation and manual calculation. To ensure that the results are the same
2. 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 – Swinburne Method) #

Manual Excel Spreadsheet

MiTS Software

Select storage type to be used at the site #

• Below-ground storage
• Formula used to calculate PSD and SSR (referring to below-ground storage formula)

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

• Area: 0.687 ha
• 100 m of overland flow
• 520 m flow in an open drain
• Catchment area average slope 1%
• MSMA 1st Edition

Determine the amount of impervious and pervious areas draining to the OSD storage system #

Pre-development

• Impervious = 0 ha  
• Pervious = 0.687 ha

Post-development

• Impervious = 0.4809 ha
• Pervious   = 0.2061 ha

Determine the time of concentration, tc and tcs #

Refer design chart 14.1 Nomograph for Estimating Overland Sheet Flow Times, toFrom Design Chart 14.1, tc = to + td = 10 min

In MiTS softwareUsing Time of Concentration for Natural Catchment Equation 14.6Calculated from Equation 14.6, tc = 10 min

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 = CIAP30  = 48.091 mm, P60 = 62.045 mmPd = 32.32 mmHence, I = Pd/tc = 32.32 / (10/60) =193.94 mm/hrQp = 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 = CIAP30  = 48.09 mm, P60 = 62.05 mmPd = 32.32 mmHence, I = Pd/tc = 32.32 / (10/60) =193.94 mm/hr, Qp = CIA = 0.230 m3/s

Calculate the Post-Development flows, Qa

Post-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 = CIAP30  = 48.091 mm, P60 = 62.045 mmPd = 38.04 mm. Take tc as nearest = 15 min. Hence, I = Pd/tc = 38.04 / (15/60) =152.18 mm/hrQa = CIA = 0.23 m3/s

Post-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 = CIAP30  = 48.09 mm, P60 = 62.05 mmPd = 38.04 mmHence, I = Pd/tc = 38.04 / (15/60) =152.18 mm/hr, Qa = CIA = 0.230 m3/s

Determine the required PSD for the site

(Equation 19.1 with Equations 19.1c and 19.1d for below-ground storage)

Determine the required SSR for the site

(Equation 19.2 with Equations 19.2c and 19.2d for below-ground storage)

Therefore, the required SSR (with 20% added for safety factors) = 161.314 m3

Therefore, the required SSR (with 20% added for safety factors) = 161.075 m3

Determine storage Dimensions