Drainage design tools

Transcription

1 Drainage design tools Richard Kellagher This presentation Designing drainage systems > Conveyance >Storage > Infiltration > Interception > Exceedence Assessing outline designs (planning) Checking detailed designs Page 2 1

2 Outline design illustration Pipes Swales Infiltration basins Attenuation basins Permeable pavements Attenuation basins Flood zones Overland flood flow Page 3 Conveyance (Pipes) Pipe sizing > Short duration storms Site specific hydrology FEH rainfall > No flooding 1:30 years Automated design Page 4 2

3 Basin / Pond sizing > Long duration storms > 1:100 year containment 1:1 yr &1:100 year for streams 1:1 yr & 1:30 yr for Sewers? Storage (basins & ponds) > Head discharge relationship dictates volume > Initial design > Detailed design Page 5 Long Term Storage Extra runoff due to development Understand the basis of the criterion > 1:100 yr 6 hour event > Design as infiltration If not > Design with 2l/s/ha maximum discharge rate > Function of soil type > Does pervious are contribute runoff? Vol.(m 3 /ha.mm) Vol.(m 3 /ha.mm) Proportion of impermeable surface SOIL 1 SOIL 2 SOIL 3 SOIL 4 SOIL Proportion of impermeable surface SOIL 1 SOIL 2 SOIL 3 SOIL 4 SOIL 5 Page 6 3

4 Long Term Storage Requires detailed design modelling tools > Prove volume is activated for events 1:100 year 6hr 24 hr Page 7 Infiltration Maximise infiltration >1 100yr return period > Long duration event BRE365 Ciria RP156 Tricky integrated detailed design > Requires explicit modelling of all components Page 8 4

5 Permeable pavements Voids ratio 0.3 Storage depth > 300mm > 100+mm rainfall stored >~100 yr, 24hr event Page 9 Interception No official guidance (yet) > Understand the basis for the criterion > Deemed to comply Infiltration units Rainwater harvesting Swales Green roofs Permeable pavements Even lined > Modelling? probably not worth doing As long as all paved surfaces are specifically considered Page 10 5

6 Rainwater harvesting Water supply >(Interception only) Stormwater management? >Y/D <0.95 > Contribute to LTS Design to BS8515 (not yet revised) SR736_Developing Stormwater Management using Rainwater Harvesting_R2-0 Page 11 Overland flow / Exceedence Site topography > Failure Bigger events Failed systems Infiltration units Blockage Embankments Page 12 6

7 Assessment Tools >Greenfield runoff rate estimation > Storage volume estimation >RWH design for stormwater control > Other hydraulic tools > Site evaluation > Costing. (in progress) Page 13 Greenfield runoff estimation Updated EA report: RF-RO management for new developments W5-074 Page 14 7

8 Greenfield runoff estimate Input data > Location click > Site area > Over-ride options Rainfall parameters Soil type (HOST) Rainfall parameters (FSR) FEH / FSR uplift factor Climate change uplift Output information > Qbar > 1:1 yr > 1:30 yr > 1:100 yr Page 15 Greenfield runoff estimate Calculations > IoH 124 (FSR, 1994) > FEH Statistical equation (2008) Assumptions > Minimum flow rate 5 l/s > Minimum Qbar 1 l/s/ha > Uses SPRHOST in both cases > Hydrological region growth factors Page 16 8

9 Storage estimate Interception storage Attenuation storage Long Term Storage Treatment storage Also reporting > Qbar and > Discharge rates > 1:1 yr > 1:30 yr > 1:100 yr Page 17 Storage estimate Input data > Location click > Site area > Impermeable area >50% > Long Term Storage choice Over-ride options > Soil type (HOST) > Rainfall parameters (FSR) > SAAR > FEH / FSR uplift factor > Climate change uplift > Urban creep factor > Interception depth Page 18 9

10 Greenfield runoff estimate Calculations > IoH 124 (FSR, 1994) > FEH Statistical equation (2008) > Uses SPRHOST in both cases > Hydrological region growth factors > Attenuation storage adjustment for not using Long Term Storage Qbar = 2l/s/ha Assumptions > Minimum flow rate 5 l/s > Minimum Qbar 1 l/s/ha > Rainfall parameters M / 17 / 20mm r 0.2 / 0.3 / 0.4 > Treatment storage 15mm UK Vt (Scotland and NI) > 80% paved, 0% pervious infiltration for LTS Page 19 Rainwater harvesting tool - stormwater Page 20 10

11 Tank Storage behaviour Storage behaviour f(y/d) must be <0.95 Page 21 Individual house Input data > Roof area > Number of bedrooms > SAAR (annual rainfall) > Design rainfall depth Over-ride information > Statistical no. of occupants Mean Standard deviation > Number of events/yr > Runoff loss coefficients Page 22 11

12 Individual house Output >Tank size required Y/D ratio Compliance % Page 23 Rainwater harvesting - Multiple properties Multiple property types Numbers of each type of house >Number of bedrooms etc > Output as for individual property >% compliance enables calculation of attenuation and Long Term storage requirements Page 24 12

13 Other Hydraulic tools Infiltration design > Design individual systems Soakaway / infiltration trench Joint probability analysis > Floodplain issues Critical duration of site drainage & river Summer / Winter runoff Page 25 HR Wallingford Howbery Park, Wallingford, Oxfordshire OX10 8BA, United Kingdom tel +44 (0) fax +44 (0) info@hrwallingford.com 13