603 - 5885 1250 (4 lines) info@mes100.com

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

OSD Rational Method (MSMA 1)  

  1. Project file MiTS 1(PondCAD) here
  2. Project file MiTS 2 here
  3. Software Report here
  4. Manual Excel Spreadsheet here
  5. 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 – Rational 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 minIn 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-Development1. Calculate rainfall depth,P30 and P60  using Equation 13.22. Determine FD from Table 13.33. Calculate Rainfall Intensity using Equations 13.3 & 13.44. Calculate Qp = CIAP30  = 48.091 mm, P60 = 62.045 mmPd = 32.32 mmHence, = Pd/tc = 32.32 / (10/60) =193.94 mm/hrQp = CIA = 0.230 m3/sPre-Development1. Calculate rainfall depth,P30 and P60  using Equation 13.22. Determine FD from Table 13.33. Calculate Rainfall Intensity using Equations 13.3 & 13.44. Calculate Qp = CIAP30  = 48.09 mm, P60 = 62.05 mmPd = 32.32 mmHence, = Pd/tc = 32.32 / (10/60) =193.94 mm/hrQp = CIA = 0.230 m3/s

Calculate the Post-Development flows, Qa

Post-Development1.Calculate rainfall depth,P30 and P60  using Equation 13.22. Determine FD from Table 13.33. Calculate Rainfall Intensity using Equations 13.3 & 13.44. Calculate Qp = CIAP30  = 48.091 mm, P60 = 62.045 mmPd = 38.04 mmTake tc as nearest = 15 minHence, = Pd/tc = 38.04 / (15/60) =152.18 mm/hrQa = CIA = 0.231 m3/sPost-Development1.Calculate rainfall depth,P30 and P60  using Equation 13.22. Determine FD from Table 13.33. Calculate Rainfall Intensity using Equations 13.3 & 13.44. Calculate Qp = CIAP30  = 48.09 mm, P60 = 62.05 mmPd = 38.04 mmHence, = Pd/tc = 38.04 / (15/60) =152.18 mm/hrQa = 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) = 157.392 m3Therefore, the required SSR (with 20% added for safety factors) = 161.075 m3

Determine storage Dimensions

Powered by BetterDocs

× WhatsApp Help