Designing for Exceedance in Urban Drainage : Good Practice
This guidance aims to provide best practice advice for the design and management of urban sewerage and drainage systems to reduce the impacts that arise when flows occur that exceed their capacity. It includes information on the effective design of both underground systems and overland flood conveyance. It also provides advice on risk assessment procedures and planning to reduce the impacts that extreme events may have on people and property within the surrounding area. The broad objective of the guidance is to improve engineers, planners and designers appreciation of the risks associated with urban drainage systems and their understanding of how these risks may be mitigated. It provides guidance so that systems can be designed to safely and sustainably accommodate periods when the design capacity of drainage systems are exceeded during extreme events. The guidance will be relevant to areas drained by piped systems or SUDS.
- Paperback | 257 pages
- 200 x 297mm
- 23 May 2006
- Construction Industry Research & Information Association (CIRIA)
- London, United Kingdom
- Illustrations, maps
Table of contents
1 Introduction to the guidance; 1.1 Aims and objectives of the guidance; 1.2 Limitations of this guidance; 1.3 Structure of the guide; 1.4 Sources of information; 1.5 Associated publications; 1.6 Background to drainage exceedance; PART A OVERVIEW; 2 The process of exceedance and definitions; 3. Stakeholder roles and drainage performance; 3.1 Drainage stakeholders; 3.2 Managing extreme events in existing urban areas; 3.3 The role of the planner and developer in new developments; 3.4 Drainage design and performance standards; 3.5 Key stakeholder lessons; 4. Effective management of exceedance 25; 4.1 Identifying above ground flood pathways 25; 4.2 The capacity of surface pathways; 4.3 Providing surface storage; 4.4 The effect of building layout; 4.5 Impact on downstream systems; 4.6 Post event clean up; PART B. DETAILED DESIGN; 5 Managing stakeholder interaction; 5.1 The planning process; 5.2 Stakeholder responsibilities; 5.2.1 Local authorities; 5.2.2 Sewerage undertakers; 5.2.3 Environmental regulators; 5.3 Stakeholder consultation process; 5.3.1 Initial stakeholder consultation phase; 5.3.2 Stakeholder consultation phase; 5.4 Good practice in stakeholder interaction; 5.4.1 Glasgow East urban flooding; 5.4.2 Yorkshire property flooding solutions; 5.4.3 Flooding of residential area in Birmingham; 5.5 Ownership and legal rights; 5.6 Education - the public as stakeholders; 5.7 Flood warning; 5.8 Stakeholder collaboration; 6 Runoff from natural catchments; 6.1 Introduction; 6.2 Natural drainage processes; 6.3 Rainfall; 6.3.1 Spatial rainfall; 6.3.2 Seasonal rainfall; 6.4 Rural runoff; 6.4.1 Characteristics of rainfall and rural runoff; 6.5 Models for estimating rural runoff; 7 Hydrological processes and the effects of urbanisation; 7.1 Hydrological processes; 7.1.1 Introduction; 7.1.2 Interception; 7.1.3 Depression storage; 7.1.4 Infiltration; 7.1.5 Surface flow; 7.1.6 Evaporation and evapo-transpiration; 7.2 Runoff; 7.3 Stream network and channel morphology; 7.4 Floods in natural catchments; 7.5 The effects of urbanisation; 7.6 Urban runoff behaviour; 7.7 Urbanisation and Flooding; 8 Runoff from urban catchments; 8.1 Urban Runoff models; 8.1.2 The constant (Old UK) runoff model; 8.1.2 The variable (New UK) runoff model; 8.1.3 The fixed percentage runoff model; 8.2 Estimation of the difference between greenfield and development runoff; 9 Interaction between major and minor systems; 9.1 Principles of interaction; 9.1.1 Flooding from manholes and other drainage connections; 9.1.2 Limitation of inlet capacity; 9.1.3 Surface run-off from pervious area; 9.2 Calculating exceedance flow; 9.3 Calculating flows in surface flood pathways; 9.3.1 Surface run-off; 9.3.2 Adding run-off from permeable areas; 9.3.3 Surface conveyance; 9.4 Calculating drainage inlet capacity and exceedance; 9.4.1 Highway gullies; 9.4.2 Roof drains; 9.4.3 Yards and other paved area drainage gullies; 9.4.4 Applying limiting inlet capacity to calculate exceedance flows; 9.5 Inlet capacity of SUDS systems; 10 Developing a risk assessment; 10.1 An introduction to Exceedance Flood Risk Assessment; 10.2 Components of the EFRA; 10.3 Determining the risk value. 10.3.1 EFRA Process; 10.3.2 Selection of the appropriate EFRA level; 10.3.3 Level 1 EFRA - Simple small areas 10.3.4 Level 2 EFRA - Large or complex areas; 10.3.5 Level 3 EFRA - Large and complex areas; 10.4 Assessing the probability; 10.5 Assessing the consequence; 10.5.1 Consequence hierarchy for building types or land use as a result of flooding; 10.5.2 Damage to property; 10.5.3 Damage due to depth; 10.5.4 Damage due to depth and velocity; 10.5.5 Health and Safety; 10.5.6 Loss of facility / business; 10.5.7 Emergency services; 10.5.8 Social implications; 10.6 Calculation of risk; 11 Designing for surface conveyance; 11.1 Principles of design; 11.2 Identifying flood pathways; 11.3 Designing flood channels; 11.3.1 Channel conveyance; 11.3.2 Velocity and depth of flow; 11.3.3 Cross section details; 11.4 Channel transitions; 11.4.1 General principles; 11.4.2 Transition between single channel reaches; 11.4.3 Road junctions; 11.4.4 Inlets; 11.4.5 Outlets; 12 Designing for surface storage; 12.1 Principles of design; 12.2 Storage area design process; 12.2.1 Size; 12.2.2 Health and safety; 12.2.3 Maintenance; 12.2.4 Outfall design; 12.2.5 Diversion control design; 12.3 Types of storage areas; 12.3.1 Storage options hierarchy; 12.3.2 Additional storage in SUDS; 12.3.3 Car parks; 12.3.4 Minor roads; 12.3.5 Playing fields, recreational areas and parkland; 13 Building layout and detail; 13.1 Design principles; 13.2 Building type and layout; 13.2.1 Layout and flood pathways; 13.2.2 Utilising existing features of the site; 13.3 Building detail; 13.3.1 Building in protection measures; 13.3.2 Property elevation / threshold levels; 13.3.3 Selection of the building materials; 13.3.4 Venting; 13.3.5 Entrance details; 13.3.6 Driveways and cartilage; 10.3.7 Siting of services; 13.3.8 Inadvertent modifications to existing flood pathways; 13.3.9 Under building flood paths; 14 Downstream impact assessment; 14.1 Conveyance and storage; 14.1.1 Flood conveyance impacts; 14.1.2 Conveyance with storage; 14.2 Procedure for assessing and mitigating impacts; 14.3 Assessing the impact on downstream systems; 14.4 Mitigating the effects of downstream impacts; 15 Case study 1: Bishopbriggs South; 15.1 Introduction; 15.2 Stakeholder Involvement; 15.3 Calculating exceedance flow; 15.3.1 Collecting data; 15.3.2 Using models to assess system performance; 15.3.3 Verifying against historic flooding; 15.3.4 Upgrading to a Level 3 study; 15.4 Exceedance risk assessment; 15.5 Solution development; 15.6 Impact on downstream systems; 16 Case Study 2: Upton - Northampton; 16.1 introduction; 16.2 Stakeholder Involvement; 16.3 Drainage of Developed Areas; 16.4 Interaction between the minor and major systems; 16.5 Risk Assessment; 16.5.1 Collecting data and building a hydraulic model; 16.5.2 Assessing system performance (1 in 30 year return period - 0.033 annual probability); 16.5.3 Assessing system performance (1 in 100 year return period - 0.01 annual probability); 16.5.4 Assessment of risk outside school; 16.6 Building layout and detail; 16.6.1 Amending building layout and threshold levels; 16.7 Impact on downstream system; 16.7 Conclusions; Appendix A: Modelling exceedance; A.1 Surface flood pathways; A.2 Surface flooding; A.3 Modelling inlet capacity; A.4 Modelling flood risk; A.5 Further guidance; Appendix B: Exceedance flow at highway gully inlets; Appendix C: Conveyance in surface flood pathways; C.1 Introduction; C.2 Flood pathway channels; Appendix D Assessment approach to determine flood volumes and rates from SUDS; D.1 Assessment approach; D.2 Hydrology; D.3 Pervious pavement performance; Results; Application of results and conclusions; D.4 Swale performance; Contributing area; Gradient of the swale; Length of the swale; Outflow control from the swale; Application of results and conclusions; D.5 Infiltration system performance; Application of results and conclusions; Appendix E Generic guidance on assessing flood volumes and rates from, SUDS; E.1 Assumptions, Inflow, Outflow, Storage; E.2 The principles of the flood estimation method; E.3 Method of application; E.4 Check against modelling results, Pervious pavement, Infiltration trench, Swale; Appendix F Design example of a permeable pavement; G.1 Rational method; G.2 The TRRL method (Young and Prudhoe1973), G.3 Flood Studies Report (FSR) - (NERC, 1975); G.4 FSSR 6 - Flood prediction for small catchments; G.5 Poots & Cochrane method, 1979; G.6 The ADAS method (Agricultural Development and Advisory Service, 1980); G.7 The SCS method (Soil Conservation Service, 1985 - 1993); G.8 Institute of Hydrology Report No. 124 (1994); G.9 Flood Estimation Handbook, FEH, (1999); G.10 Statistical procedures for flood estimation; G.11 Rainfall-runoff method for flood estimation; G.12 Advantages and disadvantages of the flood estimation handbook techniques; G.13 FSR and FSSR 5 and 16 percentage runoff estimation; G.14 FEH runoff model - variable percentage. runoff; References; British and international standards; UK Legislation and regulations; Legal rulings; Glossary; Abbreviations.