Stakeholder Consultation

Transcription

1 Project SC Stakeholder Consultation 23 rd September 2010 Project Background Paul Samuels - HR Wallingford The previous MAFF projects Research commission at HR Wallingford and the former IoH Wallingford from about IWEM Water Practice Manual No 7 Chapter 6 led by Peter Charnley (North Level IDB) Reports produced at recommendation of ADA Technical Committee Engineering Guide (EX 331) Research Summary report (EX 330) Compilation of all documents (EX 353) Copies with MAFF, ADA, CIWEM, ICE Page 2 1

2 Changes since 1993 Major national floods in 1998, 2000/01, 2007 Reviews by Peter Bye and Sir Michael Pitt Consultants and IDBs do modelling Widespread computing Spatial data and GIS FEH replaced FSR for flood hydrology in 2000 IDB reorganisation and rationalisation Environment Agency adopted risk-based approaches Making Space for Water policy (2004) Flood and water management Act (2010) Page 3 The current Environment Agency project objectives To develop guidance for practical risk assessment approaches for pumped drainage systems for use in: Catchment Strategies Strategic Planning - capital programme National Flood Risk Assessments Environment Management Plans Where assessment of risk from artificial drainage is significant Page 4 2

3 The current project objectives To provide scientific guidance on how to adopt this within Agency risk modelling tools. To provide updated guidance on appropriate flood risk assessment methods for lowland drainage systems For use by IDB engineers Aim for consistency of approach from local schemes to strategic planning Page 5 Stakeholder input ADA Technical Committee contributed informally to the project scope Environment Agency and ADA membership of project board Workshop 1 (June 2010) Provide understanding of the issues and challenges which are being faced in pumped catchments Workshop 2 (September 2010) Provide input to the emerging methods Page 6 3

4 Project SC Stakeholder Consultation 23 rd September 2010 Update of Engineering Guidance Jaap Flikweert - Royal Haskoning Introduction Key Objective: Translate the results of the project s research into practical guidance Scope Update existing MAFF Guidance Incorporate results of other project tasks: Hydrology Risk-based approach Interaction between pumped systems and overall catchment Additional user needs? Page 8 4

5 Aim of this session: Introduction Introduce proposed changes to the guidance Get feedback and steer Page 9 Feedback from user workshop Aim of first workshop (9 June): Understand current use of the guidance & alternative approaches Identify specific needs for the guidance Questionnaires & Feedback on the day Page 10 5

6 Overall set-up Feedback from user workshop Should not be enforced ; flexible Common source of best practice Need for context Hydrology Need clear guidance on use of FEH Trapezoidal Unit Hydrograph & flexible Tp Urban areas Page 11 Hydraulics Feedback from user workshop Range of methods to suit requirements Hydrology is bigger uncertainty Pumping systems Less need for guidance on optimising tariffs Other issues Seasonality (variable Manning; different event type) Assessing consequences of flooding Page 12 6

7 The Hydraulics and Hydrology of Pumped Drainage Systems (Paul Samuels, HR Wallingford, November 93) MAFF Guidance Produced at ADA s request To translate research into practical guidance Set up by design step Page 13 Overall structure of the guide Two dimensions Hydrology Hydraulics Pump capacity and operation Asset management Appraisal Consents Land use planning Page 14 7

8 Context Asset management: fi PAS55 Appraisal: fi Appraisal guidance Planning: fi PPS25 Page 15 Asset information Asset management Performance & risk assessment Planning From PAS55 Page 16 8

9 Probability x Consequences Risk based approach Portfolio of approaches Reducing probability or consequences Structural / non-structural Dealing with uncertainty Flexibility / Robustness Probabilistic approaches Focus on asset performance Page 17 Overall structure of the guide Two dimensions Hydrology Hydraulics Pump capacity and operation Asset management Appraisal Consents Land use planning Page 18 9

10 Explain use of FSR / FEH method..and where not to use it. Hydrology Page 19 Hydrology Discharge, cumecs per 10 mm of net rain Qp Tp Tp 1.5 Tp 2 Tp 2.5 Tp Time, hours Trapezoidal unit hydrograph: Adapted from IWEM manual, 1988 Includes channel storage! Avoid duplication with hydraulic model Other issues: Urban areas Subcatchments Percentage run-off Page 20 10

11 Hydraulics: Other topics Update from 1993 to 2011 Link with vegetation management Storage: double counting with trapezoidal UH Pumping capacity and operation Update from 1993 to 2011 Link with recent / ongoing studies (e.g. Pumping efficiency) Page 21 Programme End of November: Draft guidance February 2011: Final guidance Page 22 11

12 Project SC Stakeholder Consultation 23 rd September 2010 Risk-based methods Caroline Mc Gahey - HR Wallingford What are the challenges we face? What is the existing risk? Where is it? What are the drivers? What is the future risk? What is the changing risk in the system? What choices for management response and development location are sustainable, robust, affordable & adaptable? Page 24 12

13 Why undertake risk-based modelling? Models support rational decision making by: Providing an objective understanding of system behaviour Providing richer information (drives down costs) Promoting focused dialogue between stakeholders Page 25 Why undertake risk-based modelling? The decision makers: Need to utilise judgement and experience but Cannot intuitively determine what approach is best Page 26 13

14 The traditional response to floods in the Thames (picture courtesy: Rachael Hill, Environment Agency) Page 27 Tydd Pumping station, North Level IDB pumps, 13 m 3 s new pump after 1947 floods, 16 m 3 s new pump, increase rpm, electrification, Photos courtesy Internal Fire - Page 28 after 1968 wet year, Assessing 20 m 3 s -1 flood risk in pumped catchments Museum of Power 14

15 Traditional methods Single events e.g. 100 yr Deterministic Fixed state of flood risk system Assumes assets (defences, pumps) perform to design standard or fail Sources - Pathways Outputs are in terms of hazard e.g. water levels, flood extents Risk-based methods All Return Period events Probabilistic Multiple flood risk system states (failed/non-failed combinations) Considers performance of assets Sources - Pathways - Receptors Outputs include hazard, exposure and risk Page 29 A system-based approach (RASP as currently applied nationally) Pathway (e.g. defence) Receptor (e.g. people in the floodplain) Source (River or sea) Page 30 15

16 Example Outputs Probability of Inundation >0m (POI) Page 31 Example Outputs Risk (Expected Annual Damages ) Page 32 16

17 Risk attribution to individual defences Source: Gouldby and Sayers, 2006 Page 33 Pumped catchments are different Catchment Low-lying, flat, artificial, locally complex Channels Layout, undefended Pumps Type, capacity, layout, reliability, operation Seasonality Varying resistance, operational rules, crops Page 34 17

18 High-level carrier tributary High-level carrier Flood Sources Pumping station Floodplain area of interest Flood Pathways Run-off Channel flow to pump Pumped water to high-level carrier Raised defences Overflow/breach from high-level carrier Page 35 Flood Receptors People Property Agriculture Critical infrastructure Page 36 18

19 Channels - capacity, blockage Defences - performance Critical components Pumping Stations - performance, capacity, screens Page 37 High-level carrier tributary High-level carrier Outputs Probability of Inundation High Medium Low Pumping station Floodplain area of interest Raised defences Page 38 19

20 High-level carrier tributary High-level carrier Outputs Risk High Medium Low Pumping station Floodplain area of interest Raised defences Page 39 Conclusions Flood risk management system is complex Decisions are increasingly complex Flood risk managers require structured methods and guidance Risk-based analysis supports this through: considering performance of the system presenting rich unbiased evidence on flood risk proving a means to explore the impact of change on flood risk Page 40 20

21 Feedback questions Comments on suggested approach? Have we missed anything? Additional requirements for guidance? Page 41 More Feedback Come and see us at the HR Wallingford exhibition stand! Feedback through the ADA Technical Committee Page 42 21