Agenda item

Report of the Superintendent of Hampstead Heath relative to the results of the first major task undertaken by the Design Team in relation to the Hampstead Heath Ponds Project.

The Committee is asked to consider and comment on the outcome of the Design Flood assessment. 

The Superintendent of Hampstead Heath introduced the report before the Committee relative to the results on the first major task undertaken by the Design Team in relation to the Hampstead Heath Ponds Project and the Fundamental Review of the basis for the whole project.  The report before Members set out the details of the Design Flood assessment and Members views were sought thereon.

Following an earlier presentation to the Heath Ponds Project Stakeholder Group by Dr Andy Hughes (Panel Engineer on the Fundamental Review) on 18^th March 2013, written queries in respect of technical aspects of the project were submitted to Atkins.  An updated list of questions was tabled to Committee Members and further questions were invited by no later than the evening of Wednesday, 10^th April 2013.  The Committee noted that following submission to Atkins, responses would be provided in advance of the special meeting of the Hampstead Heath Management Committee on 29^th April 2013. 

Ian Harrison (Vale of Health Society and Chairman of the Stakeholder Group) updated the Committee about the Stakeholder Group’s progress to date.  He felt that the group was now working well and, even before seeing Atkins’ new, lower, flood projections, had a good prospect of reaching consensus on at least the majority of key issues.   The new flood assessment was very encouraging but Stakeholder Group Members felt that a face-to-face meeting with Atkins was vital if full confidence was to be established that the revised assessment was soundly based.  Such a meeting was offered for April but might now be deferred to May but this was not deemed to be acceptable.  More generally, if the Stakeholder Group was to be able to inform to a great degree the deliberations and discussions of the Consultative Committee, it was essential (not least in order to reduce any risk of subsequent judicial review challenge), that they have adequate time and information to be able to reach properly considered conclusions at each stage of the process, even if this ultimately meant stretching the existing City of London decision-making timetable.  Given how well the Stakeholder Group was working, it would be a tragedy if avoidable time constraints were to prevent proper decision-making and input. 

In noting Mr Harrison’s comments, the Chairman confirmed that a discussion about the Design Flood assessment would not take place at the Hampstead Heath Management Committee on 15th April 2013 but would instead take place at a special meeting on 29th April 2013.  At this stage, the views of the Consultative Committee and the Stakeholder Group would be taken into account.  The Committee was therefore invited to submit any additional queries by no later than Wednesday evening to ensure that all responses were submitted to Atkins. 

Dr Andy Hughes then delivered a short presentation to the Committee in respect of the Fundamental Review of the basis of the project undertaken by Atkins and explained how they had determined that whilst works were still essential to reduce the City of London’s liability and meet its duty of care to communities south of the Heath, the size of potential floods in “extreme rainfall events” was less than those derived by previous hydrology consultants.  He also outlined the consultation activities that had been undertaken to date, and those planned in the future, involving the Stakeholder Group. 

Dr Andy Hughes provided an overview of the Design Flood assessment and the Fundamental Review, highlighting the sympathetic approach to the works that would be taken and the balance that would have to be sought in respect of minimising the risk of dam failure and damage resolution; and environmental soutions.  Commenting on the Panel Engineer requirements, it was noted that best practice led solutions had to be delivered and future modelling would be intended to address both short and long term considerations.  The Committee was advised that more accurate calculations to those previously used by Haycock Associates had been reviewed and an industry standard hydraulic modelling package used which would be beneficial both now and in the longer term.  Such calculations enabled the team to predict how the water would affect the dams both flowing over and around them.

In respect of the flood assessment, it was noted that the recent calculations differed to Haycock Associates and a reduced flow of water was now anticipated which, in turn, meant that less engineering works were anticipated. Following a brief explanation about over-topping and peak velocities of water through the dam, Dr Hughes explained that whilst works were required, they may not be required on all dams.  Consequently, the current position was that the least amount of works as possible would be undertaken. 

Dr Hughes outlined the current options available in respect of the Ponds Project and explained that, in light of the need to meet best practice and satisfy existing standards, there were two approaches:- (1) the legislative approach and (2) the non-legislative approach- with the second option favoured as it enabled a holistic approach to providing the best solution for the Heath.  Thereafter, the focus of the project would be on identifying suitable options such as minimising engineering solutions, raising dams and consideration of the ponds as a whole rather than in isolation.  In terms of next steps, Dr Hughes stressed the need to identify those schemes that would reduce the flow of water and focus on the appropriate engineering solutions.

A number of questions were raised following the presentation:-

Referring to future liability considerations and case law precedent, Dr Hughes outlined the implications of Rylands and Fletcher, common law and the Reservoirs Act in respect of managing the situation at Hampstead Heath and went on to explain that a risk based approach would ensure that the best solutions were identified across the dams and with minimal impact. 

In noting that some damage of a dam was acceptable but failure was not, a Member of the Committee asked as to what extent of damage would be acceptable.  Dr Hughes explained that the matter was very complex and that the current situation in respect of over-topping was very uncertain.  He further explained that some over-topping could be acceptable subject to velocity and duration levels.  Consequently options to minimise over-topping and reduce velocities and duration, whilst minimising hard engineering, would be based on judgement taking into account the comprehensive hydrology results.   Responding to a question about the implications of vegetation on the dams, Dr Hughes explained that natural growth on dams did not necessarily mean that they would fail.  Consequently whilst it was hoped that as much vegetation could be retained on dams across the Heath, the conditions needed to be as favourable as possible and therefore the situation would be carefully managed.  

Following a query about the Kenwood Ponds and how these had been factored into the peak velocity figures, Dr Hughes explained that the Kenwood system had been modelled even though this did not fall within the Corporation’s remit.  Dr Hughes further explained that the ponds were already over-topping and whilst discussions with English Heritage had taken place, the focus remained on the Heath ponds.  Simon Lee (Superintendent) explained that meetings had been conducted with English Heritage and that works to the two ponds in Kenwood had been undertaken in 2006/07.  It was noted that English Heritage was aware of its current responsibilities.

Following a question in respect of future flood risk to surrounding neighbourhoods as a result of any future works up-stream, Dr Hughes explained that the future works would not compromise the surrounding neighbourhoods in any way.  Simon Lee advised the Committee that this was a critical issue and that discussions had taken place with Thames Water and the London Borough of Camden at a past Stakeholder Group meeting regarding the surface water drainage issues.  Paul Monaghan (City Surveyor's Department) advised the Committee that whilst the Corporation would continue to work closely with Camden and provide assistance where necessary, it would not compromise its own objectives and/or risk increased liability.

Referencing earlier discussions in respect of the existing legislation, the apparent hierarchy between different Acts and the implications for liability as a result of competing legislation, a Member of the Committee asked whether a response had been received from DEFRA.  Dr Hughes explained that he had written to Ministers and DEFRA but that no responses had yet been received.  He advised that in respect of the Corporation’s legal obligations, Counsel’s opinion had previously been sought. 

Following a query about why Atkins’ run-off percentage calculations differed to those previously provided by Haycocks and Binney's, a brief explanation was provided about Atkins’s calculation methodology.  It was suggested that default values may have been quoted in the past, thus leading to a figure of 90% and 27% respectively, as opposed to Atkins’s figure of 76%. 

In respect of calculating loss of life, Dr Hughes explained that this was very complicated, taking into account a wide range of issues and variables such as velocity and duration levels, the type of  property and whether people were located at home during the daytime.  Loss of life is then evaluated across the variables to determine both low and high extremes, taking into account legislative requirements.  

A query was raised about the decision-making process and how the future options for each dam would be considered in the context of all of the ponds rather than in isolation.  Dr Hughes advised that the views of the Stakeholder Group and the Consultative Committee would be fed back to the Management Committee so that all views expressed thus far were taken into account.  In respect of the next steps the committee noted that all of the possible options would need to be quickly but carefully considered, taking into account best use of the sites and a desire to minimise impact.   It was noted that the Committee felt that sufficient time should be built into the process to ensure that people were fully briefed about, and able to comment on, the options as they emerged.  Dr Hughes and the Chairman acknowledged the complexity of the issues and the need to provide people with as much information as possible.  The Chairman stated that following consideration of the long list of options by the Stakeholder Group, the constrained list needed to be reviewed and refined so that appropriate options could be agreed in the future.

Following an earlier request at a meeting of the Stakeholder Group, a Committee Member requested an expanded map of flooding areas. 

RESOLVED:- That –

(i)         the Consultative Committee’s comments in respect of the Hampstead Heath Ponds Project –Design Flood Assessment be noted and;

(ii)        any additional questions be submitted in writing to the Superintendent, Hampstead Heath by no later than 10^th April 2013 so that written responses could be provided ahead of the special meeting of the Hampstead Heath Management Committee on 29^th April 2013.