Climate adaptation, innovative SuDS and protection of Harrestrup Å

1. Climate adaptation, innovative SuDS and protection of Harrestrup Å Retrofitting Baunebakken, Hvidovre By Sille Lyster Larsen, Grontmij & Vinni Rønde, MSc Hydrology, Wageningen UR

2. Introduction 2 l/s/ha Hvidovre

3. Whatwas done • Hydraulic model • Calibration with flow and rainfallmeasurements • 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 Increased permeable surface

4. Retrofitting the system

5. Rain gardens and filter trench

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

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

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

9. Method: Irrigation experiment Water from fire hydrant was sprayed on the roofs with flow rates equal to:

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

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

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

13. 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

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

15. 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 • uncertainty in flow • design errors • variation in ratio roof area / rain garden area

16. 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 areable to convey a 5-year return periodrain of 10 min duration

17. 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

18. Conclusion • The overall design is being implemented and expected to be completed by August/September 2014

19. Thankyou • Vinni Rønde, vikar@student.dtu.dk • SilleLarsen, sll@grontmij.dk