Agenda item

PROPOSAL: Application for approval of details subject to conditions 29 (surface water drainage) and 31 (foul drainage) of planning permission 17/00852/OUT.

OFFICER RECOMMENDATION: Discharge.

40.2          This application was for the approval of details subject to conditions 29 (surface water drainage) and 31 (foul drainage) of planning permission reference 17/00852/OUT. The Chair indicated that a representative from the Lead Local Flood Authority (LLFA) was present to answer any technical questions in respect of drainage and flood risk.

40.3          In presenting this application the Planning Officer stated that in approving the reserved matters application for 74 dwellings on this site at the October Planning Committee Members had requested that the drainage details, which are reserved by condition, attached to the outline permission, come before the Committee for determination. Accordingly, approval was sought for conditions 29 (surface water drainage) and 31 (foul drainage) attached to the outline permission. Following consultation with the LLFA it was advised that the submitted information showed a suitable modelled surface water drainage scheme and included a report on the state of the culvert in the A38 that would be the receiving water body for the discharge of the surface water from the site. Additionally, the maintenance plan showed that critical infrastructure was to be adopted by Severn Trent to ensure maintenance would be carried out for the lifetime of the development. The LLFA was therefore satisfied that the submitted details were acceptable and had recommended that conditions 29 and 31 could be discharged.

40.4          The agent for the application addressed the Committee informing Members that the accepted Drainage Strategy Plan under the Flood Risk Assessment, which accompanied the outline planning permission for the Yew Tree Farm development, presented a surface water connection to the existing adopted foul water drainage. He indicated that this approach had been accepted by the Local Planning Authority and Severn Trent Water under the outline approval. Following the submission of the reserved matters application, the applicant had been asked by the LLFA and Severn Trent Water to investigate alternative discharge points due to capacity matters within the existing foul water network. The Agent indicated that, in consideration of local concerns, his client, who despite acquiring the site based on an approved outline drainage strategy, agreed to explore other points of discharge. A pumped discharge to Brook Lane to the east of the site was considered, however following conversations with Severn Trent Water this approach was discarded due to issues with third party land and legal difficulties with the coordination of a sewer requisition agreement. Nevertheless, a connection to Brook Lane would increase the risk of flooding downstream and would exacerbate any issues related to blockages of the existing ditch; this site naturally fell to the north-west and surface water runoff from the greenfield catchment terminated in the A38 via existing road gullies. Therefore, for these reasons, this option was deemed unviable. Following a request from the LLFA a connection to the existing culvert under the A38 was then investigated. The Agent stressed that, at considerable cost to his client, CCTV survey works were undertaken to establish the condition of this culvert and it was proven that this was in fact a culverted watercourse which was subject to the 1991 Land Drainage Act. The LLFA’s recommendation was to then mimic the behaviour of the existing greenfield catchment and establish a connection to the existing culverted watercourse under the A38 at greenfield runoff rates. Additional volumes from the development would be attenuated and controlled within the development via the proposed attenuation basin. The proposed drainage design mimics the behaviour of the existing catchment and would not increase flood risk elsewhere. The on-site drainage system had been designed in accordance with the latest legislation and guidance where ample on-site storage had been provided. In conclusion the agent stated that his client and their engineers had worked vigorously with the LLFA throughout this process and at an additional cost to them had presented a robust and acceptable scheme.

40.5          The Development Management Team Leader (North) read to Members an objector’s speech which thanked the Committee for allowing him to yet again make a representation on this reserved matter issue. He indicated that he did so in the light of ongoing concerns around drainage and flood risk to the site and the surrounding area into which these proposals would drain and particularly conditions 29 and 31. He informed the Committee that he had studied the drainage survey in detail and could not see how Members could have confidence that the issues raised previously were now mitigated. The study was full of comments and photographic evidence of a drainage system not fit for purpose for a development of this scale, indeed words such as obstacles, broken pipes, defective connections, joints displaced and fractures appeared throughout the survey report. The whole network was in disrepair and the issues could be seen even before the development was built out. The LLFA had originally objected to the drainage plans for this development and rightly so; he could not see how the LLFA could now accept the plans given the drainage report that had belatedly been carried out. A report that demonstrated a crumbling network with limited capacity to deal with surface water even despite the sop of an attenuation basin as part of the SUDS design. The Members who represented the area knew its problems with dealing with ever increasing flood risk given both pluvial and fluvial events. He indicated that Members were aware of the history of this area not just in connection with 2007 and 2014 but even as recently as this year. This, and the surrounding area, were frequently subjected to flooding, the very watercourses this development was to drain into were frequently under water due to rising levels and water from elsewhere across the catchment where it could hang for days sometimes weeks on end. The objector could not see that things had changed here if anything it further demonstrated the need for a rethink and some major investment on and offsite to provide any confidence to the local community that flood risk had been mitigated and their lives would not be further blighted. In conclusion he indicated that Members were aware of the errors of the past but, in this case, there was an opportunity to mitigate the risks and insist on a far greater amount of work on the network prior to any build out; if the developer wanted this then there was a duty to ensure that their development did not increase the risk elsewhere. The objector could see nothing in the proposals before the Committee that convinced him, or those residents that had to live with the risks, that this was the case.

40.6          A Member referred to paragraphs 5.2, 5.4 and 5.5 of the Officer’s report which stated “A pumped system consisting of an adoptable pumping station and rising main would be required. This would be offered for adoption to Severn Trent Water”. The reference to adoption being offered to Severn Trent Water appeared in all three of the paragraphs referenced and, on that basis, she wished to ask if the network was crumbling, as maintained by the objector, who would be responsible for getting it upgraded and making it acceptable for Severn Trent to take it over and adopt it; in fact she wondered whether they would actually adopt it. She also referred to the proposed pumping station and rising main in relation to the issues this had caused with another development in Tewkesbury when it had flooded heavily in 2007. Additionally, there had been problems with other pumping stations in particular the one at Deerhurst when the Council had been responsible. She also referred to the drainage management strategy which included a maintenance schedule which would be undertaken by a private management company for the length and lifetime of the development. She questioned what would happen if the private company went bust; would Severn Trent Water also take over that maintenance responsibility. The representative from the LLFA indicated that Severn Trent Water would adopt the surface water management on the site which would be as far as the outflow to the A38 culvert. He indicated that whilst the wording did say it would be offered for adoption there had been extensive discussions with Severn Trent Water which had been made more difficult with changes in legislation and directions as to what would be accepted in terms of SUDs, but in June there had been a new direction which meant that Severn Trent Water would now be able to adopt the attenuation basin and pumping station. As Members were aware this was a difficult site to drain as the path to Twigworth was fairly flat and the pumping station was necessary to take surface water from the underground drainage from the properties up into the attenuation basin and then onto the discharge point out to the A38.  This was a realistic proposition and with the adoption of the pumping station there was no reason to believe that it should be unacceptable or in any way dangerous. There was an exceedance routing plan which would slow the surface water if it did not get pumped and the balancing pond was exceeded; it would flow along the road paths down to the A38 and get into the same culvert through the road gullies. There were a lot of legislative problems and in particular there was an issue over whether the Government was prepared to accept the recommendations of the Pitt Report and the 2010 Flood and Water Management Act as was the case in Wales but with the current legislation in place the proposition for private management of the public spaces with Severn Trent Water adopting the drainage was what the LLFA would be expected to accept. The Member indicated that she still had concerns and questioned whether there had been any legal agreement drawn up for Severn Trent Water to adopt the drainage system. The LLFA representative stated that there was not currently a signed legal agreement but there would be; the developer was designing the system in line with the requirements of Severn Trent Water and working closely with them as was the LLFA. He indicated that his main problem previously had been the suggestion that the discharge should go to the watercourse in Brook Lane and if that could not happen then it would go into the foul sewer which was the worst possible solution as that would require pumping as well. Every solution to get the surface water from this site would require pumping and this solution with Severn Trent Water adopting the pumps was the best solution. It was now up to the developer to work with Severn Trent Water during the build out to ensure that the way they built was satisfactory to Severn Trent Water. Whilst he understood the concerns and would have welcomed a solution where there were SUDs adoption bodies under the 2010 Flood and Water Management Act, which would allow these issues to be sorted in advance, sadly the Government had not implemented schedule 3 of the Act which therefore resulted in the current situation. A Member raised queries on the maintenance plan and, in particular, he referred to the monthly inspection of inlets, outlets and overflows for blockages to be cleared as required and the inspection of inlets and facility surface for silt accumulation which was scheduled for monthly in the first year and annually thereafter or as required; he wondered whether this was sufficient bearing in mind that shopping trolleys frequently ended up in inlets causing a silt build up and then flooding as was the case in areas of Bishops Cleeve. The representative from the LLFA indicated that the major silt build ups occurred immediately after the build out whilst there was still material from the development process which was loosened and moveable resulting in the requirement for reduced scheduling of silt checking is appropriate later in the lifetime of the development. As far as shopping trolleys were concerned, he agreed they were a nuisance but hoped that residents would notify the authority of such obstacles so that action could be taken for them to be cleared under the 2010 Flood and Water Management Act. A Member stated that his questions related more to do with what happened when the water left the site and in particular the culvert as Severn Trent Water was going to look after everything on the site. He indicated that when you looked through the culvert there were multiple external pipes coming from other areas of Twigworth but he was unable to see anywhere calculations from these to show that they had been included in the capacity of the culvert. In addition the culvert emptied into Hatherley Brook along with other areas and he queried whether the cumulative impact of all these areas emptying into the Brook had been assessed and whether there would be any implications on these areas. Finally, he asked about the state of repair of the culvert as there were sections of it that were not fit for purpose as indicated by the objector. He highlighted just a few of the problems on a 10 metre stretch which included multiple fractures, blockages, broken pipes, visible soil and settled deposits. This highlighted that there was serious work which needed to be done on the culvert. The Member referred to condition 29 which stated that no development shall commence on site until a detailed design, maintenance and management strategy for a sustainable surface water drainage system had been submitted to, and approved by, the Local Planning Authority. The reason for this was to ensure the development was provided with a satisfactory means of drainage thereby preventing the risk of flooding. It was important that these details were agreed prior to the commencement of development as any works on site could have implications for drainage, flood risk and water quality in the locality. On this basis, he maintained that the repair and bringing up to standard of the culvert was part of the detailed design strategy to be able to drain the site yet he could not find anywhere or in any documents how this was to be done. He maintained that this needed to be in place prior to development commencing as realistically it was not possible to sign off condition 29 without this work on the culvert being fully documented in the plan. In order to fulfil the condition to the level required to satisfactorily sign off its objectives, work to bring the culvert up to standard needed to be included. The LLFA representative indicated in response that the A38 culvert and the state of it was not a matter for the developer, he maintained that the Member’s interpretation of the state of the culvert was somewhat different to his; a lot of the blocked pipes were not affecting the flow of the culvert itself many of them were feeding pipes which affected the feed into the culvert and in terms of fractures this was a common problem with culverts which resulted in the necessity for an assessment to be made on the state of them. The LLFA representative stated that having made that assessment he was of the view that the culvert was fit for purpose and whilst some maintenance would be necessary this would be the responsibility of the riparian owners. Negotiations were currently taking place with Gloucestershire Highways in order to get their agreement that they were the riparian owner. In addition, one of the reasons that the culvert was not known previously was that it had not been causing any problems. There was no reason to believe that the culvert did not have capacity to take water from the Yew Tree Farm site, which it was probably taking already from the highway gullies because that was the natural flow of the land. The LLFA representative stressed that he did not agree with the interpretation that the culvert was not fit for purpose and he was of the view that, provided the discharge from this site to the culvert was managed through a properly engineered solution, it would probably provide betterment for the area rather than make things worse. Another Member in thanking the LLFA representative for his comprehensive answers indicated that he had major concerns with regard to water flows. He referred to the fact that the LLFA representative had indicated that Twigworth was fairly flat and maintained that this was before the strategic A1 site had been built at 750mil above the original ground level. He referred to the problems with water being retained on the A1 site during the build out resulting in the need for it to be pumped on a regular basis into the Hatherley Brook and he questioned whether this additional water flow had been taken into account as part of this development. In addition the road gullies for the Yew Tree Farm site were on the right hand side and there were no gullies on the left hand side yet the land was higher on the right so the water was flowing into Sandhurst Lane and subsequently flowing into ditches and drains that were already blocked. He referred to Page No. 48 of the Officer’s Report and in particular paragraph 5.5 and indicated he was unsure as to which report Members had seen but on Page No. 8 of the drainage survey report there was a picture of a brick culvert which was in a state of collapse with one brick sitting on the ground as opposed to the roof of the culvert and the report also showed that the pipes were between 5% and 40% blocked which was ridiculous and he had no confidence that the existing system would be able to handle the amount of water that this particular area suffered from. He also asked for answers in relation to the additional flow rates being added by the pumping of the A1 site into the existing water course. The LLFA representative indicated that the natural flow from the Yew Tree Farm site was towards the A38 and from the A38 it drained into the A38 culvert so, if the scheme controlled the surface water flow from the Yew Tree Farm site to the greenfield runoff rate or lower, it would reduce the flow to the A38 culvert. Currently the flow from the site was not managed it was just flowing off the land onto the highway full of mud and silt that was getting into the culvert. The flow was not being increased it was being managed in a better way than through the natural process. The Member indicated that he had been told this in respect of the A1 site yet it was having to be pumped out on a regular basis and therefore he was not convinced by the response given and had very big misgivings about the impact of this scheme and the information being given. He referred to the Innsworth phase 1 site and indicated that Members had been told that water would be retained on that site yet when there was heavy rain, Innsworth Lane flowed like a stream which had never happened before. In terms of water being retained on the site, the LLFA representative stated that this would not be forever as the water would need to be discharged to the watercourse at some point; whilst the infrastructure was completed that would be via pumping but it was still a managed outflow whether it was pumped or managed as it would eventually be through hydro brakes and the attenuation basins.

40.7          The Development Manager stressed that the key question to answer in respect of this application to discharge the conditions was whether there was a drainage system which would prevent this development having a greater impact on flood risk. This was about managing the water on the site and the water leaving the site. The drainage experts were satisfied that there was a mechanism in place through the drainage strategy to make sure that was the case. He understood the concerns locally about the existing infrastructure and that was something that the infrastructure providers would need to look at going forward; he was prepared to write to those organisations responsible for the management of the system outside of the site. However, the fact remained that the information provided in respect of this site showed that the amount of water leaving the site would be no greater than the greenfield position as it stood and that was what needed to be demonstrated to satisfy this condition. A Member indicated that he had been given assurances that the flow rates from the strategic A1 site would be the same as existing before the build started but this was not the case. In addition, contaminated water was being pumped into the Brook which, when reported to the Planning Department, complainants were told that this was the responsibility of the Environment Agency. However the Member could not accept this as it was a condition imposed by this authority that the flow rates would remain the same and this was not the case. The Development Manager indicated that there appeared to be some confusion between a drainage scheme that would be in place once a development had been completed and that of a building site; he was aware of discussions across the County as to whether there were ways which authorities could better control sites once they were under construction but, as it stood currently, the advice provided that it was an Environment Agency matter if there is evidence that a watercourse was being polluted was correct. He acknowledged that it was a difficult position whilst development was ongoing but if someone was suffering increased flood risk and suffering damage as a result that was a matter between them and the landowner, this was the advice consistently given. It was for the Committee to decide whether there was a drainage scheme which, once development was completed, would not increase flood risk elsewhere and there was evidence that this had been provided and was agreed and supported by the Council’s technical experts. A Member indicated that it was inevitable that this matter would cause great concern to Members in view of the area. However, he wished to clarify his understanding of the position; things had moved on from the original position of the LLFA in objecting to the proposals which had been based on an inadequate drainage plan to a system that was now approved and involved surface water being held in an attenuation pond and then pumped out into the culvert on the A38 and then onwards the Hatherley Brook in a regulated manner in a way which meant that there would be no excess flooding beyond the A38 culvert. The LLFA representative confirmed that this was the case; it mimicked the greenfield runoff rate and it was going to the same place as it was at the moment but in a more controlled manner by pumping from the attenuation basin. Further questions were asked about the flow off the site following a rainstorm and concern that the water would not go into the pond but straight onto the road system; completion of the survey from where it had ended to the Hatherley Brook, the drainage outlet at the back of the Schoolhouse and the impact on that property as it was about 8ft from the backdoor of that property and the problems with the use of electricity to pump water when there was a power cut. The LLFA representative indicated that, having seen the section of the culvert which had been surveyed, he felt that it was a reasonable indicator of the state of the rest of the culvert which did show signs of wear because of its age but he did not believe that it showed a state of failure which was why he was happy to not have the whole of the culvert surveyed in order to make a judgement that the culvert was in a reasonable state. He stated that he would definitely like to see the culvert surveyed properly at some stage and would be doing more work on ensuring he was aware of who was maintaining it and that it was being maintained. It was quite interesting how little was known about this culvert at the start of the process which gave some reassurance as if there had been failures, he was sure he would have known more about it. He believed its success was the reason why little had been known about this culvert in the past. He stressed that the discharge rate from the site would be managed through the balancing pond so all the surface water from the roofs of the houses, and a lot from the highways, would go via the attenuation where it would be controlled at a steady rate before going into the A38 culvert and thus it would go in at the equivalent greenfield runoff rate. Further questions were asked about what had been included in the calculations, the cumulative impact on Hatherley Brook taking account of other developments in the area, the impact of extra water being pumped into the culvert even though vast parts of it were not in a good condition, whether when the balancing ponds were full they would be pumping any additional water into the Hatherley Brook, as was the case in Longford, which would then be heading downstream and the calculations in respect of when the water had been taken offsite which was relevant as offsite was mentioned in the condition. A Member felt that more information was required on the offsite effects of the water and what had been included in the calculations for this scheme generally. The representative from the LLFA stated that because the flow was being restricted to the same level as the greenfield run off rate, the offsite impact would be unnoticeable. There was no extra water being discharged from the site, it would be mimicking what was happening currently so there would be no increase in the discharge into the A38 sewer it was just being managed in a better way. He maintained that there was no need to do any further work on calculations as what was going into the sewer at the moment would be unchanged. A Member indicated that the current discharge was leading to flooding but the LLFA representative responded that this was due to surcharges of the foul sewer and was a huge problem but, if the surface water could reach the Hatherley Brook without going through the foul sewer, then something very useful would be achieved. Another Member spoke about the flooding events of 2007 and 2014 in this area and indicated that they had been caused by the River Severn being too high and the brooks, culverts, streams etc. being unable to empty into the river thus causing the water to back up which then caused this site in particular to be under water. He sought a cast iron guarantee that there would no adverse impact on existing or new homes should there be a repeat of the flooding events of 2007 and 2014. The LLFA representative stated that as the greenfield runoff was being mimicked there would be no increased risk to properties but if there was another one in two hundred event as occurred in 2007 then houses would flood in the area and those risks needed to be managed accordingly but the requirement was to ensure that developments were built to the one in one hundred storm event because that was considered to be reasonable. The one in two hundred events happened much less frequently and, in terms of other management beyond the one in one hundred event, then the exceedance routes were listed to ensure the water would continue to flow to the A38 and enter the culvert via the road gullies. In terms of water back up due to tidal locking, this was a well-known phenomenon and was something that was difficult to manage and, although it was managed, it would continue as long as the tides kept happening; this was taken into account when calculating whether a weather event was a one in one hundred event or a one in two hundred event. Further questions took place on drainage and flooding issues with the LLFA representative explaining in detail the design aspects of a drainage system, the modelling of flows expected in different rainfall events defined under the one hundred and two hundred events and the rain storm patterns in terms of intensity. This was how it was known whether a balancing pond was of adequate size to deal with a one in one hundred event and there would be an exceedance route which would normally follow the path down the road to the A38 and into the gullies. There would already be a certain amount of attenuation in the pond and any overtopping would follow the exceedance route which would also be the case should the pump fail. He indicated that it was this design that resulted in no increased flood risk downstream.

40.8          A proposal was put forward that a decision on condition 29 be deferred at this time for more comprehensive detailed information to be provided to give Members confidence that the drainage system for this development was not going to adversely impact on existing or new homes. The Development Manager indicated that a clear indication of the information required would be needed as the responses from the LLFA representative set out what the conditions sought to achieve and what was required to discharge them. Much of the Committee’s discussion and issues raised appeared to relate to existing problems that would remain problems once the development had been completed. A developer could not be required to deal with pre-existing problems; the information submitted demonstrated that the development “washed its own face” and the system to be put in place would essentially keep the status quo if not make things a little better. He maintained that if a deferral was necessary and for it to be seen to be reasonable then it was essential that Officers fully understood what additional information it was that Members required. He reiterated the point made by the LLFA representative that the developer of this site could not be expected to resolve existing problems with the drainage infrastructure. The proposer stated that it would be in respect of Members uncertainties about the drainage proposals, the flooding impact on existing properties, unknown information about the management company, whether Severn Trent Water would adopt the pumping station, the work to be done on upgrading the culvert and the condition of the culvert in its entirety. One Member felt that the Committee was in danger of mixing up two different issues; one in relation to existing problems in the area and the other relating specifically to this development and its impact. The proposer clarified that the deferral was being requested for further details to be provided in respect of the management and maintenance of the drainage proposals beyond that of what had already been provided and also for a survey of the entire length of the culvert under the A38 to be completed. The motion was seconded and sufficient support was received for the vote on the motion to be recorded. Debate on the need for the deferral and the sufficiency of the information already received ensued. The Development Manager stated that planning permission and reserved matters for this site had already been granted and this application was for approval on drainage and water management. The scheme presented had been designed in consultation with the LLFA and Severn Trent Water and was a strategy that was acceptable to those technical experts. He fully understood the concerns of the local community and the wider infrastructure issues which were significant, and required all relevant agencies to be involved in addressing, but the Committee was being asked to look at this specific site and the drainage proposals that related to it. The developer had done what had been asked and demonstrated what was required to the satisfaction of the experts. He indicated that, from an Officer perspective, it would be unreasonable to defer the application for further information as he did not think anything further could be provided that could add to the debate.

40.9          Upon the motion being put to the vote, it was recorded as follows:

40.10        The motion was declared to be lost.

40.11        A motion was proposed to accept the Officer recommendation which was seconded and, upon being put to the vote, it was

RESOLVED          That conditions 29 (surface water drainage details) and 31 (foul                              drainage details) be discharged in accordance with the Officer                              recommendation.

40.12        The meeting adjourned at 11.30am for a short break.

40.13        The meeting reconvened at 11.40am with the same membership present.