CLIMATE ADAPTATION, INNOVATIVE SUDS AND PROTECTION OF HARRESTRUP Å By Sille Lyster Larsen, Grontmij & Vinni Rønde, MSc Hydrology, Wageningen UR Retrofitting Baunebakken, Hvidovre 1

Hvidovre Introduction 2 2 l/s/ha

What was done Increased permeable surface -Hydraulic model -Calibration with flow and rainfall measurements -Terrain analysis -Is subsurface flow possible? -Designing the SuDS -Iterative design process: design and functionality -Public involvement in Baunebakken -Creating ownership and getting feedback -Cost analysis -Testing traditional pipes versus SuDS 3

Retrofitting the system 4

Rain gardens and filter trench 5

Design of rain gardens Grundkær 6: Filling material: soil Drainage: pipe Size: 1,5x1,5m Vegetation: plants Grundkær 8: Filling material: Top: soil Btm: pebble gravel Drain: gravel spillway Size: 2x2m Vegetation: plants Grundkær 10: Filling material: Top: soil/stones Btm: pepple gravel Drain: stone well Size: 1,5x2m Vegetation: grass Grundkær 4: Filling material: soil Drain: pipe and gravel spillway Size: 1,5x1,5m Vegetation: plants 6

Plan view of rain gardens Outlet to sewer network roof 7 Rain garden

Plan view of experimental setup roof Outlet to sewer network Inlet Location of flow measurements 8 Rain garden roof

Method: Irrigation experiment Rainfall events Return period (year) Duration (min) Climate factor Intensity (L/s/ha) ,43226 Water from fire hydrant was sprayed on the roofs with flow rates equal to: 9

Method: water level measurements soil pebble gravel drain pipe short piezometer for surface water measurements gravel spillway long piezometer for water level measure- ments in the bottom 75mm pipe trench water from roof permeable membrane diver 80cm 10

Results: Grundkær 4 -Drain pipe not in use during the 5-year return period event -Overflow during 10-year return period event 11

Results: Grundkær 6 -Overflow during 5- and 10-year return period events -Lekage to penetrating piezometer  error in bottom water level 12

Results: Grundkær 8 -Overflow during 5- and 10-year return period events -Design error: level of spillway higher than level of lowest edge of rain garden 13

Results: Grundkær 10 -No overflow -OBS: Reduced flow to rain garden due to overflow of rain gutter 14

Summary of results -Volume capacity of rain gardens was far from reached during a 5- and 10-year return period of 10 and 20 min duration, respectively. -Infiltration is the limiting factor in rain gardens with plants  Ponding and overflow occurred -Direct comparison of rain gardens is difficult o uncertainty in flow o design errors o variation in ratio roof area / rain garden area 15

Final design of rain gardens The grass rain garden: -Rain garden similar to that at Grundkær 10 -Reduction of depth from 80 to 50 cm (decrease of material expenses) The plant rain garden: -Rain garden similar to that at Grundkær 4 -A drainpipe has been excluded due to risk of clogging in the long run  With these designs the rain gardens are able to convey a 5-year return period rain of 10 min duration 16

Conclusion -Climate change adaptable system -The required volume was found through decentralized SuDs elements -Runoff delayed to 2 L/s/ha  protection of Harrestrup Å -Lower cost than a traditional pipe design 17

Conclusion -The overall design is being implemented and expected to be completed by August/September

Thank you 19 -Vinni Rønde, -Sille Larsen,