Agenda Reports Pack (Public) 15/10/2012, 19.00 - Meetings ...

Agenda Reports Pack (Public) 15/10/2012, 19.00 - Meetings ... Agenda Reports Pack (Public) 15/10/2012, 19.00 - Meetings ...

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as from information provided by residents and businesses that have sufferedfrom flooding in the past, in order to map and model surface water flooding, andhence identify high risk flooding areas. The Task Group were concerned that thisdata was insufficient as it was not a true reflection of the actual flooding risk in theborough. This concern arose from the fact that the Task Group were made awarethat many people affected by flooding chose not to report it, primarily but notsolely because of concerns relating to the potential impact on property prices andinsurance premiums.1.4. The Pitt Review commissioned analysis of a number of different approaches tomodelling surface water flooding; examining their effectiveness and undertaking abasic cost-benefit analysis. The results of this work are set out below.1.5. The five approaches considered by the Pitt Review were:iiiiiiivvTopographic index analysis – This is a basic terrain model with no rainfallinput. There is no correlation between the model’s outputs and areas ofknown flooding, and so it would be of little use.2D overland routing of uniform rainfall event – This model makes noallowance for differences in rainfall, and assumes that every area has auniform capacity to drain water. It could be used for high level analysis butsignificantly overestimates the extent of flooding.Decoupled sewer model and 1D overland routing – This model takesaccount of the effect of drainage by using a detailed sewerage network model.It is the most accurate method of identifying properties on water companyregisters but underestimates the spatial extent of flooding.Decoupled sewer model and 2D overland routing – This model includes2D surface runoff data and detailed sewerage network data, but does notinclude assessment of below-ground flooding mechanisms. It produces amuch better estimate of the spatial extent of flooding but fails to identify someproperties on water company registers.Coupled sewer model and 2D overland routing – This model combinessurface runoff data, detailed sewerage network data and a full 2D model ofabove-ground flooding. It does not include below-ground floodingmechanisms but this could be added. It gives a very accurate assessment ofthe spatial extent of flooding but fails to identify some properties on the watercompany registers.1.6. The Pitt Review made a number of comments regarding the modelling approaches:i. Tools exist that can reliably and accurately model surface water flooding inurban areas.ii. The cost of the different models can vary widely owing to the information anddetail required. Additionally the cost of accurate modelling can be high ifmodels of sewerage networks have to be built from scratch.iii. Simplified modelling is possible at relatively low cost but is far less reliableand probably only suitable for high level risk assessments on an area widebasis. Such approaches are not suitable for assessment at the level of detailof individual streets or for producing solutions to flooding.iv. Surface water flooding can be accurately modelled and mapped but furtherwork is required to understand user needs and the costs associated withmeeting those needs.- 14 -Page 173

1.7. The Environment Agency has carried out research into developing a surface waterflooding alert system. The Environment Agency is well placed to provide a modellingand warning system to cover surface water flooding. Whilst surface water modellingis still in its infancy the Environment Agency is working with its partners to developthe tools and techniques required to model surface water flooding and it is hopedthat a significantly more sophisticated modelling system will emerge from thisprocess.1.8. The Task Group did not feel it would be appropriate, at this time, for the Council toseek to develop and implement its own surface water flooding modelling, other thanthe modelling required as part of the update of the Surface Water Management plan,which will also be used to fufill the Council’s requirements to map Flood Risk Areasby 2013, as required under the Flood Risk Regulations. This work will be undertakenby the consultants as part of the Surface Water Management Plan updatecommission. The result of this modelling will also be used by the EnvironmentAgency to develop further modelling techniques. The Task Group took this view inlight of the costs of establishing and implementing an effective flood risk modellingsystem, both in terms of the costs of designing a modelling system and in terms ofthe costs of engaging with third party consultants to assist existing in-houseexpertise put such a model together.1.9. The Council has appointed Clare Share as Flood Risk Manager and, in addition toher, has other officers who have some experience and expertise in flood risk,particularly in the planning department. The Task Group were impressed that theCouncil has already appointed a Flood Risk Manager and noted that other LeadLocal Flood Authorities had not been as pro-active as the Council in recruitingadditional flood risk expertise. The lack of flood risk engineers in public sectororganisations was identified by the Institution of Civil Engineers in their report entitledEngineering Skills for Flood Risk Management 3 (2004).1.10. The Pitt Review, through discussions with local authorities and engineeringprofessions, recognised four key factors as to why this was the case.i. Low salary levels for flood risk engineers, particularly in the public sector.ii. The lack of perceived value given to working for local authorities.iii. The requirement in many posts to carry out a broad range of roles, such asstakeholder engagement, rather than focusing on core engineering skills.iv. The simple shortage of suitably qualified graduates.1.11. The Task Group acknowledge that the Council is able to rely upon consultantengineers but notes that in the long run there may be very real benefits to havingadditional in-house expertise.1.12. The Task Group felt that the Council should maintain a close working relationshipwith the Environment Agency. The Environment Agency currently engages withnumerous parties who are responsible for different aspects of the drainage andsewerage systems – including water companies, internal drainage boards, highwaysauthorities, navigation authorities and riparian owners. This will help theEnvironment Agency understand how surface water runoff is discharged by the3 http://www.ice.org.uk/Information-resources/Document-Library/Engineering-skills-for-flood-riskmanagement- 15 -Page 174

1.7. The Environment Agency has carried out research into developing a surface waterflooding alert system. The Environment Agency is well placed to provide a modellingand warning system to cover surface water flooding. Whilst surface water modellingis still in its infancy the Environment Agency is working with its partners to developthe tools and techniques required to model surface water flooding and it is hopedthat a significantly more sophisticated modelling system will emerge from thisprocess.1.8. The Task Group did not feel it would be appropriate, at this time, for the Council toseek to develop and implement its own surface water flooding modelling, other thanthe modelling required as part of the update of the Surface Water Management plan,which will also be used to fufill the Council’s requirements to map Flood Risk Areasby 2013, as required under the Flood Risk Regulations. This work will be undertakenby the consultants as part of the Surface Water Management Plan updatecommission. The result of this modelling will also be used by the EnvironmentAgency to develop further modelling techniques. The Task Group took this view inlight of the costs of establishing and implementing an effective flood risk modellingsystem, both in terms of the costs of designing a modelling system and in terms ofthe costs of engaging with third party consultants to assist existing in-houseexpertise put such a model together.1.9. The Council has appointed Clare Share as Flood Risk Manager and, in addition toher, has other officers who have some experience and expertise in flood risk,particularly in the planning department. The Task Group were impressed that theCouncil has already appointed a Flood Risk Manager and noted that other LeadLocal Flood Authorities had not been as pro-active as the Council in recruitingadditional flood risk expertise. The lack of flood risk engineers in public sectororganisations was identified by the Institution of Civil Engineers in their report entitledEngineering Skills for Flood Risk Management 3 (2004).1.<strong>10</strong>. The Pitt Review, through discussions with local authorities and engineeringprofessions, recognised four key factors as to why this was the case.i. Low salary levels for flood risk engineers, particularly in the public sector.ii. The lack of perceived value given to working for local authorities.iii. The requirement in many posts to carry out a broad range of roles, such asstakeholder engagement, rather than focusing on core engineering skills.iv. The simple shortage of suitably qualified graduates.1.11. The Task Group acknowledge that the Council is able to rely upon consultantengineers but notes that in the long run there may be very real benefits to havingadditional in-house expertise.1.12. The Task Group felt that the Council should maintain a close working relationshipwith the Environment Agency. The Environment Agency currently engages withnumerous parties who are responsible for different aspects of the drainage andsewerage systems – including water companies, internal drainage boards, highwaysauthorities, navigation authorities and riparian owners. This will help theEnvironment Agency understand how surface water runoff is discharged by the3 http://www.ice.org.uk/Information-resources/Document-Library/Engineering-skills-for-flood-riskmanagement- <strong>15</strong> -Page 174

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