Sustainable Urban Drainage

1. Sustainable Urban Drainage Alan Jones (Alan.Jones@ed.ac.uk)

2. Sustainable Drainage • A concept that focuses on the environment and people. • Considers: • Quantity of runoff • Quality of runoff • Amenity value of surface water • Existing urban drainage systems are: • Unsustainable in the long-term • Damaging to the environment

3. Why are SUDS needed? Peak discharge becomes larger Floods occur quicker due to reduced infiltration Hydrograph: Discharge Time • SUDS: • Attenuate flow • Promote infiltration & groundwater recharge

4. 11% of Scottish river length is classified as polluted due to contamination from urban drainage Why are SUDS needed? SUDSWP (2000) • SUDS aim to protect watercourses from point/diffuse pollution by acting as sinks for contaminants • Cost implications for maintaining long-term performance of SUDS

5. Why are SUDS needed? Amenity • A ‘loaded term’ when used in relation to SUDS – environmental/community issues Covers: • Aesthetic & Ecological quality of the landscape • Land-use • Wildlife habitats • Land-values • Recreation opportunities • Educational opportunities • Water-resources Other factors: • Opportunity costs • Perceptions of risk • Construction impact

6. SUDS ‘Triangle’

7. Present Legal Status • WFD – Water Framework Directive (2000) • Prevent deterioration in water status • Restoration of surface waters to good ecological and chemical status by 2015 • Reduction of pollution from priority substances • Contributing to mitigating the effects of floods and droughts • Preventing/limiting pollution input into groundwater • CAR – The Water Environment (Controlled Activities) (Scotland) Regulations (2005) • Surface water-runoff in areas constructed, or construction sites operated, after 1st April 2006 must now be drained by a Sustainable Urban Drainage System • Exceptions – Single dwellings or if the discharge is to coastal water

8. Conventional Drainage Precipitation: Rainfall/Snow Rapid conveyance of water & pollutants Local watercourse

9. SUDS Drainage: The ‘treatment train’ approach • Connect SUDS together • Individual function of local SUDS techniques beneficial – but design should be led by a holistic vision & approach • Combined integrated function – mimics the waterflows in the natural hydrological cycle: • Surface Flow • Infiltration • Storage in water-bodies • Interflow • Evapotranspiration

10. Treatment Train • Good Housekeeping: best practice to eliminate, or minimise, pollutants being generated and allowed into the environment. • Source Controls: methods of dealing with runoff at source, e.g. permeable paving, filter strips, or roadside filter trenches. • Site Controls: local controls that deal with generally smaller catchment areas, e.g. detention basins. • Regional Controls: larger components that might typically deal with larger catchments and upstream site controls, e.g. stormwater wetlands and retention ponds. (Heal, 2004)

11. A variety of techniques Drainage conveyance Kerb design Roof drainage reuse Detention Basins Filter Drain Swales

12. Retention Ponds Falkirk Stadium Retention Pond (Undeveloped catchment)

13. Retention Ponds / Wetlands Lidl Distribution Centre, Livingston - Retention Pond (Loading bay, Carpark runoff)

14. Tackling Contaminants • The flood-reducing benefits of SUDS are obvious... • Store water at various points in the catchment and allow water to be re-used, infiltrated, released slowly and/or evaporated. • These processes also allow the trapping of potential contaminants (e.g. metals, PAHs/Hydrocarbons) within the treatment train. • Contaminants are typically adsorbed (physico-chemically bonded) to sediment particles that are entrained in flow. • As water speed is slowed down using SUDS, particles (and therefore contaminants) settle out.

15. Contaminant Sources: Vehicles • 15-fold increase in the number of car and taxi miles covered over the last 50 years! SUSTAINABLE (?) Campbell et al. (2004)

16. Land-Use & Contamination (Beasley and Kneale, 2002)

17. Design - Site Constraints • Physical site constraints can make construction difficult or impossible, and maintenance expensive if not addressed adequately. Factors to consider include: • topography - e.g. steep slopes • soils and geology - e.g. erosivity, porosity, depth to bedrock or instability • groundwater - e.g. geochemistry and water table depth • space - limited open space, proximity to underground services. (e.g. gas, power) • Social constraints include issues of health and safety, aesthetics and impacts on recreational facilities. Factors to consider include • odour problems • visual impacts • noise • physical injury - resulting from unauthorised access to structures; • contamination - infection, poisoning or injury caused by trapped pollutants or algal blooms • vermin - e.g. mosquitoes, rats.

18. Design – Maintenance Issues • Not only can a poorly maintained SUDS technique function ineffectively, it can become a source of pollution or flood hazard itself. • When designing a SUDS measure, the following points should be considered: • ease of maintenance and operation - the selected treatment should be easy and safe to maintain and operate • extent of maintenance - ensure the maintenance requirements are within the operator's capability • access to the treatment site - consider the ease of site access, when reviewing the treatment's maintenance requirements • frequency of maintenance - ensure that resources are available to carry out maintenance at the required frequency • debris and pollutant clearing - during clearing, the treatment should not require direct human contact with debris and trapped pollutants (automated clearing options are preferred) • disposal - consider the disposal requirements of any waste from the treatment process.

19. Case Study: J4M8 • SUDS development (c. 2000) • Previously agricultural land • Now a distribution hub based mid-way between Edinburgh and Glasgow

20. J4M8 Oblique Aerial Photograph Reddinghill Bing (Landscaped, but still burning) Phase 1 Retention Pond Aldi Distribution Centre M8 Motorway Former Scottish Courage Distribution Centre