URBAN CLIMATE CHANGE GUIDELINES HOW TO ACHIEVE SUSTAINABLE ADAPTATION IN URBAN AREAS. 2016 Greve Forsyning, VandCenter Syd, PH-Consult and DHI CONTENTS 1 Introduction ........................................................................................................ 1 1.1 Background .......................................................................................................................... 1 1.2 Purpose ................................................................................................................................ 2 1.3 Definition of the problem ...................................................................................................... 2 1.4 Legislation ............................................................................................................................ 4 1.4.1 Sewerage plan ..................................................................................................................... 4 1.4.2 Sewer renewal plan ............................................................................................................. 4 1.4.3 Contingency plan ................................................................................................................. 4 1.4.4 Additional municipal planning, local plans, plans for water quality, etc. .............................. 5 1.4.5 Risk assessment and analysis of extreme rain .................................................................... 5 1.5 Flood Directive ..................................................................................................................... 6 1.5.1 Preliminary flood risk assessment ....................................................................................... 6 1.5.2 Flood hazard and flood risk maps ........................................................................................ 7 1.5.3 Flood risk management plans .............................................................................................. 7 1.5.4 Publication of maps, plans, etc. ........................................................................................... 7 1.5.5 Summary .............................................................................................................................. 8 2 Status of knowledge on climate change ........................................................... 9 2.1 Projections of future climate change .................................................................................... 9 2.1.1 Projections of future climate change in Denmark ..............................................................10 2.2 Obtaining climate change projections ................................................................................12 2.2.1 Global climate model projections .......................................................................................12 2.2.2 Regional climate model projections ...................................................................................12 2.3 Estimates of future rainfall .................................................................................................12 2.3.1 Estimates of future rainfall in Denmark ..............................................................................14 2.4 Future water levels in marine waters .................................................................................18 2.4.1 Future water levels in marine waters in Denmark ..............................................................20 2.5 Future water levels in lakes and rivers ..............................................................................24 2.5.1 Future water levels in lakes and rivers in Denmark ...........................................................24 2.6 Future water levels / pressures in groundwater .................................................................25 2.6.1 Future water levels/pressures in groundwater in Denmark ...............................................25 2.7 Determination of input time series data and boundary conditions - Recommendations .............................................................................................................25 2.7.1 Developing precipitation time series ..................................................................................26 2.7.2 Coupled rainfall ..................................................................................................................28 2.7.3 Other boundary conditions .................................................................................................28 2.7.4 Service level and compliance with operational requirements under the influence of climate change ...................................................................................................................32 3 Modelling of flooding from storm water system and rivers .......................... 34 3.1 From surface depression maps to sophisticated hydraulic models ...................................34 3.1.1 Model tools .........................................................................................................................34 3.1.2 Decision making process ...................................................................................................35 3.1.3 The multidisciplinary angle .................................................................................................35 3.1.4 Economy ............................................................................................................................35 3.2 Calculation methods ..........................................................................................................36 3.2.1 Terrain model - QA ............................................................................................................37 3.2.2 Surface depression maps ..................................................................................................38 3.2.3 Hydraulic surface calculations ...........................................................................................41 3.2.4 Hydrodynamic drainage model 1D.....................................................................................43 3.2.5 Combined hydrodynamic drainage model and surface model 1D-1D ...............................44 Urban Climate Change Guidelines (The Climate Cookbook for DANVA, Version 2.1) i Greve Forsyning, VandCenter Syd, PH-Consult and DHI 3.2.6 Combined hydrodynamic drainage model and surface model 1D-2D ...............................47 3.3 Comparison of methods .....................................................................................................50 4 Flooding from the sea ...................................................................................... 53 4.1 Calculation methods ..........................................................................................................53 4.1.1 Water elevation map ..........................................................................................................54 4.1.2 Water elevation map in connection to the sea ...................................................................56 4.1.3 1D-urban drainage systems ...............................................................................................57 4.1.4 1D-1D two-layered hydrodynamic model ...........................................................................57 4.1.5 Hydrodynamic calculation of flood .....................................................................................58 4.1.6 1D-2D hydrodynamic modelling of the flow on terrain combined with a hydrodynamic model of the drainage system ....................................................................59 5 Urban climate adaptation................................................................................. 61 5.1 Risk analysis ......................................................................................................................61 5.1.1 Damage assessment using a risk analysis ........................................................................61 5.1.2 Risk analysis ......................................................................................................................62 5.1.3 Risk of flooding from extreme rainfall.................................................................................64 5.2 Priority adapting to floods under a changing climate .........................................................68 5.2.1 Urban prioritisation in Greve municipality ..........................................................................68 5.2.2 Description of the method for prioritisation in Greve..........................................................69 5.2.3 Quality assurance of priority ..............................................................................................69 5.3 Options for adapting the urban drainage system ...............................................................70 5.3.1 Physical measures on drainage system ............................................................................70 5.3.2 Infiltration of storm water ....................................................................................................71 5.3.3 Separation of combined systems .......................................................................................71 5.3.4 Increasing pipe sizes .........................................................................................................72 5.3.5 Overflow .............................................................................................................................72