APPENDIX C CALCULATIONS

Transcription

1 Knowle Park, Cranleigh FRA APPENDIX C CALCULATIONS - Greenfield Runoff Estimation for Site - Calculations for Wallingford Procedure and Modified Rational Method Page 2

2 IH124 : Greenfield Peak Runoff Catchment Area AREA Standard average annual rainfall SAAR mm Soil Index (from FSR or Wallingford Procedure WRAP maps)* SOIL *SOIL is the SPR for the soil type, and for larger sites is a weighted sum of the individual soil classes for the site, where: SOIL = 0.1A SOIL A SOIL A SOIL A SOIL A SOIL5 AREA For smaller sites, use the SPR for the local soil type, as follows: SOIL TYPE AREA SOIL: SPR * The site area is less tn 50. Since the IoH124 methodology is QBAR 50 not calibrated for sites less tn 50 in area, the calculation should QBAR/ / be undertaken based on a 50 site area and proportionately adjusted QBAR site based on the ratio of the site size to Hydrological Area fig 4.2 Return Period Growth Factor (years) (table 4.3) Discrge rate Figures and table references from CIRIA C697 The SUDS Manual CIRIA 2007

3 FEH Method Knowle Park Catchment Area AREA Standard average annual rainfall SAAR mm BFIHOST FARL SPRHOST Qmed Conversion Qbar Hydrological Area fig 4.2 Return Period Growth Factor (years) (table 4.3) Discrge rate

4 Wallingford Procedure : Developed Peak Runoff Site Cracteristics Catchment Area AREA Approximate Longest Drainage Path L m 460 Difference in Ground Levels H m 3 Slope Slope (S) 1: 153 Permeable Surfaces (Rational Method runoff coefficient = 0.4) Impermeable Surfaces (Rational Method runoff coefficient = 0.95) 53% 47% Area Weighted Rational Method Runoff Coefficient 0.66 Site parameters from The Wallingford Procedure for Europe: Best Practice Guide to urban drainage modelling, HR Wallingford, July 2000 (CD) 60minute, 5 year return period rainfall M5-60 mm Ratio of M5-60 to 2day, 5 year return period rainfall r Time of Concentration Recommended Tc Method: Tc Method Choice: SCS: Sheet Flow SCS: Sheet Flow Surface Description Sheet Flow Paving or Brick Slope Sllow Roughness Coefficient (Manning's n) Flow Length, L m 460 M2-24hr mm Land Slope m/m Tc hr 0.64 Time of Concentration T c min Critical Storm Duration (minimum 5min) T crit min Critical Storm Rainfall and Runoff Z1 TC 0.80 M5-T crit 16.0 C 0.66 *Wallingford Procedure Figure 3.6 Discrge Rate Q = 2.78CiA Return Period Z2* Depth Intensity Discrge Rate (years) (mm) (mm/hr) *Wallingford Procedure Table 3.2

5 Modified Rational Method Storage Calculator Site Parameters Catchment Area AREA Approximate Longest Drainage Path L m 460 Difference in Ground Levels H m 3 Slope Slope (S) 1: 153 Permeable Surfaces (Rational Method runoff coefficient = 0.4) Impermeable Surfaces (Rational Method runoff coefficient = 0.95) 53% 47% Area Weighted Rational Method Runoff Coefficient 0.66 Site parameters from The Wallingford Procedure for Europe: Best Practice Guide to urban drainage modelling, HR Wallingford, July 2000 (CD) 60minute, 5 year return period rainfall M5-60 mm Ratio of M5-60 to 2day, 5 year return period rainfall r - Time of Concentration T c min Maximum Storm Runoff Storage Volume (modified rational method) T d 60.0 min Z1 TD 1.00 *Wallingford Procedure Figure 3.6 M5-T d 20.0 mm C 0.66 Z *Wallingford Procedure Table 3.2 M100-T d 40.6 mm Intensity 40.6 mm/hr Q d Q d,climate cnge Q limiting discrge Storage Volum Maximum storage required m Storage Volume (m 3 ) Storage Requirements Storm Duration (mins)