Risk assessment in pumped catchments

Transcription

1 Risk assessment in pumped catchments Owen Tarrant Environment Agency Jaap Flikweert Royal Haskoning Why is understanding risk to pumped catchments so important? Hull s pumped drainage and public sewerage system was overwhelmed by the extreme volume of water and the pumping system may not have been designed to cope with the design guidance for a 1-in-30 chance event. Pitt (2008) 1

2 Why have we carried out this work now? A changing management context: Defra Review of IDBs and Pitt Review Flood and Water Management Act (2010) Water Framework Directive New techniques and methods: Move from FSR to FEH New modelling methods and GIS techniques National flood risk assessment (NaFRA) Project objectives To develop 3 sets of guidance: SR1 - Scientific guidance for practical to flood risk assessment approaches to lowland pumped catchment studies. SR2 - Scientific guidance for implementation options to adopt the above methods into the Environment Agency s risk assessment toolset. SR3 - Updated best practice guidance on flood risk methodologies for lowland catchments to achieve consistency of approach from local schemes through to strategic planning. 2

3 Guide for Hydrology and Hydraulics Aim: Update MAFF Engineering Guide (Samuels, 1994) Incorporate developments since then Status: About to be published Involvement of IDB users: Involvement of users ADA representative on Project Board Workshop with 10+ IDB Engineers to determine scope Presentation of initial structure at 2010 ADA Conference Review of draft by ADA representatives Key points made: Source of good practice; not enforced guidance Provide context to technical content 3

4 Introducing the new Guide Focus on flood risk management and on engineering References for other topics No scope for new research Recommendations Some examples, but could do with more Living document Overall structure of the guide Hydrology Hydraulics Pump capacity and operation Asset management Appraisal Consents Land use planning 4

5 Chapter 2: Context Asset management PAS55 Appraisal Appraisal guidance & MCM Planning PPS25 Recent developments (post guide) Resilience partnership funding Draft National Planning Policy Framework WFD Chapter 3: Good practice approach Good practice principles (from Fluvial Design Guide): Systems approach Risk-based & performance-based approach Consider whole range of loading conditions Tiered methods: Simple methods where possible, complex methods where needed 5

6 Chapter 4: Hydrology Different methods for different purposes: Ideally, use gauged records In case of insufficient info, use Tailored FSR Rule of thumb (1.4 l/s/ha) plus growth curves useful for first indication Detailed guidance on how to apply FSR method to pumped catchments Tailored FSR method Chapter 4: Hydrology Tailored FSR method Applying FEH: Some steps the same Some steps with caveats Some steps different 6

7 Chapter 4: Hydrology Discharge, cumecs per 10 mm of net rain Trapezoidal UH, as introduced in IWEM (1988) Qp Includes storage effect of drains Tp Tp 1.5 Tp 2 Tp 2.5 Tp Time, hours New method to avoid underestimation of flood risk if used for hydraulic modelling Chapter 5: Hydraulics When to use which approach: Hydraulic analysis needed? Modelling needed? Dynamic modelling needed? 2D modelling needed? Hydraulic roughness: vegetation management and seasonality Reference to CES Roughness Advisor 7

8 Chapter 6: Pumps Guidance for number of pumps and operation Pump reliability needs further research Research needed: Next steps Hydrology of permeable catchments Application of ReFH to pumped catchments Reliability of pumping stations Fed into Joint Defra / EA R&D Programme Use the Guide as a living document Examples and case studies Regular (annual) updates 8

9 Risk assessment in pumped catchments Owen Tarrant Environment Agency Jaap Flikweert Royal Haskoning 9