Water Management and Climate Change The SuDS Protocol supported by a Socio Economic Evaluation

1. WATCHWATer management for road authorities in the face of climate CHangeNational Flood Management Conference 2019John Paul RooneyRoughan & O’Donovan Consulting Engineers

2. Water Management and Climate Change The SuDS Protocol supported by a Socio Economic Evaluation

3. The WATCH project CEDR: most important high frequency causes of road flooding • €600m annually

4. The WATCH project • CEDR call: Climate Change: From Desk to Road • September 2016 – April 2018 • Project budget • Total 275 k€ • Self investment of partners 31 k€ • Partners • Deltares (coordinator, The Netherlands) • ROD & ROD-IS (Ireland) • Egis (France) • Danish Road Directorate (Denmark) • KNMI (The Netherlands)

5. WATCH deliverables • A country comparison report showing the state of practice of existing water management and drainage approaches • Guidelines for application of climate information to be used in road drainage design and maintenance • A climate analogues tool for rainfall extremes in Europe • A protocol for adapting SuDSsystems for climate change • Guidelines for a SEA of adaptation and maintenance approaches for water management • Culminating into one document, “How to do” manual on water management assessment of resilience, understanding and applying consequences for design, inspection and maintenance

6. Country comparison • Climate change mostly not taken explicitly into account and if so: • A certain increase of intensities • Socio Economic analyses • Only on project level • Not taking climate change into account • SuDS features are used very often, mostly not as specific design feature

7. Socio-Economic Analysis Framework Socio-economic analysis essential for implementation of the WATCH outcomes • Provide arguments whether actions need to be taken • Choose optimum solution Evaluation approaches • Multi Criteria analysis • Cost Effectiveness Analysis • Life Cycle Costing • Cost Benefit Analysis

8. Criteria In the context of SuDS, key parameters which could be considered, among others include; • Cost • Technical Effectiveness (i.e. Performance) of the system • Flooding • Water quality • Amenity • Biodiversity • Space available • Adaptability to Climate Change • Maintenance regime • Technical & Organisational capacity of the NRA • Societal Impacts & Requirements • Safety Constraints & Impacts If, for example an MCA approach is adopted, then qualitative parameters would suffice.

9. SuDS Protocol for New & Existing Roads The objectives of this protocol are: • to provide guidance for assessing the resilience of Sustainable Drainage Systems (SuDS) to climate change - during periods of drought, flash flooding, temperature extremes and periods of persistent rainfall and • to propose appropriate resilient SuDS strategies to manage stormwater runoff arising from severe rainfall events now and into the future.

10. SuDS Protocol for New & Existing Roads • Description of SuDS features • Concept of the SuDS management train • SuDS features linked together • Treat and attenuate runoff close to the source • Climate change • Better treatment compared to traditional systems during intense rain • Improvement of chemical and biological treatment due to temp rise

11. SuDS Protocol for New & Existing Roads

12. SuDS Protocol for New & Existing Roads What is SuDS? SuDS offer integration with nature, by promoting: the temporary storage of surface water (ponding), infiltration, evaporation, evapotranspiration, groundwater recharge and the re-use of stormwater (Roy et al. 2008). SuDS can increase morphology, provide amenity and biodiversity value, minimise the rate and quantity of discharge and protect or enhance the quality of receiving watercourses.

13. SuDS Protocol for New & Existing Roads The Benefits of SuDS over ‘traditional’ drainage practices • Climate change predictions suggest that some types of extreme events will become more frequent, such as flooding caused by extreme rainfall, heat waves and drought. • The SuDS approach is more robust and adaptable than the traditional approach of underground piped drainage systems. • In shallow surface based systems, such as swales, water levels rise gradually and visibly. • When the capacity of the SuDS feature is exceeded, the excess water can be directed to safe storage zones. • This allows the general public, and road owners and operators to prepare for and respond to flood events more effectively.

14. SuDS Protocol for New & Existing Roads The Benefits of SuDS over ‘traditional’ drainage practices (cont) • Furthermore, shallow, visible surface based systems can be designed to offer greater flexibility to adapt to Climate Change. SuDS systems can be enhanced and maintained more readily and cheaply, compared to underground drainage systems. • Conversely, flooding from underground piped drainage systems can occur suddenly and rapidly when the design capacity is exceeded. • Lower River flows caused by drought result in reduced dilution of pollutants following rainfall events. The treatment of surface water runoff, through SuDS, helps to protect and enhance the quality of receiving watercourses.

15. SuDS Protocol for New & Existing Roads Factors Influencing the Selection of SuDS Components The key considerations are: • Site suitability, such as: soil permeability; groundwater vulnerability; sensitivity of the receiving watercourse/groundwater; groundwater levels; climate ... • Space available • Cost SuDS systems are accepted as being cheaper than traditional drainage systems for new roads, however, SuDS ‘retrofit’ schemes are considered to be more expensive when the wider ecological, social and environmental benefits of SuDS are ignored. The SEA approach can help overcome this ‘short-term’ perspective!!

16. SuDS Protocol for New & Existing Roads Factors Influencing the Selection of SuDS Components (cont) • maintenance regimes grass cutting, pruning, planting vegetation, removal of contaminated soil etc, and • community acceptance requires stakeholder engagement and education

17. SuDS Protocol for New & Existing Roads Opportunities for SuDS in a Changing Climate Principal ‘Treatment Processes’ of SuDS – Sedimentation and Biodegradation Sedimentation • Most pollution in stormwater runoff is attached to sediment particles • removal of sediment will achieve a significant reduction in pollution loading to receiving water bodies. • achieved through the reduction in flow velocities (attenuation) to a level at which the sediment particles fall out of suspension. • Care must be taken through design and appropriate maintenance regimes to ensure the risk of re-suspension is minimised during extreme rainfall events. Note: the risks are greater with ‘traditional’ piped drainage systems. Silt can be washed out of gully traps and manholes, often at depth and without the possibility of interception in a downstream SuDS feature.

18. SuDS Protocol for New & Existing Roads Opportunities for SuDS in a Changing Climate (cont) Principal ‘Treatment Processes’ of SuDS – Sedimentation and Biodegradation Biodegradation • A natural biological treatment process that is a feature of several SuDS systems - systems that are subject to both wet and dry conditions - in addition to the physical and chemical processes of SuDS systems • The level of bioremediation activity will be affected by environmental conditions such as temperature and the supply of oxygen and nutrients. Microbial communities are established in the ground using the oxygen within the free-draining materials and the nutrients supplied with the inflows, to degrade pollutants such as hydrocarbons and grease. • It is generally accepted that the chemical and biological treatment mechanisms found in SuDS systems are enhanced with increasing temperature!!!

19. SuDS Protocol for New & Existing Roads Recent Research findings: ‘wet’ and ‘dry’ systems perform best • ponds and wetlands do not benefit from the enhanced biological treatment of hydrocarbons found in the oxygen-rich conditions of the swales and basins (which are not designed to hold a permanent volume of water). • Nonetheless, ponds and wetlands have been utilised extensively as the default treatment system serving roads and motorways in Ireland and UK, with little supporting literature to justify such initiatives. • In the selection of the most resilient and enduring SuDS systems • only the suds features that experience both wet and dry conditions benefit from this added biological treatment. • Ponds and wetlands are proposed as ‘polishing stage’ options as part of a treatment train (SNIFFER, 2008).

20. SuDS Protocol for New & Existing Roads The SuDS Protocol.....Example.... Step 1 • Where the Outfall is a stream or river (the most common scenario for NRA’s). Other situations are developed in the protocol including where outfalls are; • stormwater sewers, • combined sewers, • discharge to groundwater and • ‘zero discharge’ evapotranspiration systems

21. SuDS Protocol for New & Existing Roads The SuDS Protocol – for discharge to Streams/Rivers Step 2 – Establish Allowable Discharge Rates & Water Quality Discharge Limits In New Roads, the considerations include; • At conceptual design stage, develop a ‘modular’ SuDS system, to allow for future modifications to be undertaken to respond to clanging climatic conditions or when contaminant or volumetric “trigger levels” are reached. • Sensitivity & Assimilative Capacity of receiving watercourses, • Review of River Basin Management Plans, • Control of Accidental Spillage, • Is the stream/river a source of potable water? In Existing Roads , further considerations include; • Presence of existing SuDS components, • Topography, • Space Available, • Existing pressures (such as historical flooding) arising from the existing road and /or local environmental needs Note: In existing roads, fewer ‘options’ may be available due to restricted availability of land, however, there is a greater opportunity for the designer to gather relevant data.

22. SuDS Protocol for New & Existing Roads The SuDS Protocol – for discharge to Streams/Rivers Step 3 – Determine the Most Appropriate SuDS features – based on Local Environmental Considerations • If the risk of groundwater pollution is within acceptable limits, then infiltration may be possible, subject to the findings of infiltration test results – Move to Step 4 • If the risk of groundwater pollution is outside acceptable parameters, then a ‘sealed’ system may be required. Options include: • Lined filter strips • Lined swales • Lined Detention Basin • Lined Ponds • Retention Ponds

23. SuDS Protocol for New & Existing Roads The SuDS Protocol – for discharge to Streams/Rivers Step 4 – Develop a ‘SuDS Management Train’ Scenario 1 ‘Ideal Scenario’ – Subject to Wet & Dry conditions with sufficient permeability and acceptable risk to groundwater: Filter Strip Swale/grassed channel Detention Basin Outfall Scenario 2. Infiltration not permitted due to risk of groundwater pollution: Lined Filter Strip Lined Swale/Grassed channel Lined Detention Basin Outfall

24. SuDS Protocol for New & Existing Roads The SuDS Protocol – for discharge to Streams/Rivers Step 4 – Develop a ‘SuDS Management Train’ Scenario 3 – Example of a ‘Modular SuDS System’ ……. legislation/policy dictates that a greater standard of treatment or flood resilience is required, additional SuDS components can be incorporated now or in the future, to provide Tertiary Treatment and/or greater flood resilience. Filter Strip Swale/Grassed channel Detention Basin Pond/Retention Basin Outfall Scenario 4: Subject to the findings of a monitoring regime, it may be found that more frequent maintenance of the SuDS components (e.g. grass cutting, disposal of contaminated soil and planting may negate the requirement for additional SuDS features.

25. SuDS Protocol for New & Existing Roads Maintenance Requirements for SuDS Systems In New Roads: Maintenance plans and schedules should be developed during the design phase. In Existing Roads: Specific maintenance needs should be monitored and maintenance plans adjusted to suit local requirements

26. SuDS Protocol for New & Existing Roads • Some Recommendations for Changes to the ‘Standards’ • SuDS systems which are periodically wet and dry should be the ‘default’ position • Space should be made available for additional SuDS components to be constructed in the future, in response to predicted climatic changes • Drainage designs for new and existing roads should include a maintenance regime to allow road operators to plan for and cost future maintenance requirements and upgrade works over the lifetime of the road – the ‘cheapest’ short-term solution may not be the most ‘viable’ solution – SEA approach is fundamental here • Water quality discharge limits should be stipulated in the Standards – an established practice in the US and Australia for decades. This will help to ensure that the SuDS Management Train philosophy will be fundamental to the design for roads (thus providing greater flood resilience and to help ensure compliance with the Water Framework Directive).

27. Thankyouforyour attention John Paul Rooney Roughan & O’Donovan Consulting Engineers johnpaul.rooney@rod.ie