30/08/2024
We wish to make public our most recent objection written in collaboration with the Patcham and Hollingbury Conservation Association to the Brighton Council Planning Department.
Whilst we understand that there are many, many issues with this application the most significant and devastating will be the increased risk of winter groundwater flooding for the residents of the Patcham Village.
This is significant and the applicant should look to improve the flood risk and not exacerbate it. As yet there is no satisfactory solution and for this reason the council planning committee should refuse the application next week.
Our Objection -
I write again regarding these serious issues which has not been satisfactorily resolved to meet national regulations and planning policy.
1. Prohibited Discharge of Surface Water onto or over the Public Highway
It was noted in National Highways response dated August 2023 that surface water cannot be discharged on to the Public highway by National Highways in their holding objection.
https://planningapps.brighton-hove.gov.uk/online-applications/files/FF826F7CDE273F5DB47A870CC166F65B/pdf/BH2022_02232-NATIONAL_HIGHWAYS-19102298.pdf
"The indicative drainage masterplan included in the Appendix D of Flood Risk Assessment dated in July 2022, indicates that the run-off of the site is proposed to be discharged into a combined Southern Water pipe under Vale Avenue to the south of the site entrance. However, the highway drainage records included in Figure 2.2 National Highways Planning Response (NHPR 22-12) December 2022 ´Highway drainage´ of the FRA appears to show a connection from the existing site to the highway drainage. It is illegal to carry out works within the public highway without having first undertaken/ completed all required legal agreements with us (or other relevant highway authorities), nor is it permissible to discharge surface water on to or over the public highway.”
The most recent Flood Risk assessment provided by Royal Mail states “It is proposed that runoff from the proposed adopted highway at the site entrance and the proposed adopted footpath in the south falls towards the carriageway and is drained by the existing highway drainage system.” on page 26.
They also state "Notwithstanding this, it is demonstrated that the layout can be developed to incorporate a SuDS based system that will not only provide adequate runoff protection but will also provide an improvement in the runoff quality.” on the Executive Summary.
https://planningapps.brighton-hove.gov.uk/online-applications/files/960A31A44200938F15332A44F12E11FA/pdf/BH2022_02232-FLOOD_RISK_ASSESSMENT_REV_P03-19064295.pdf
On the above point we disagree for there is not an improvement in the runoff quality. There is no significant runoff from the site, minor runoff occurs from the existing entrance but the majority of surface water collected on site stays on site and drains into the aquifer. The solution provided by the applicant to improve runoff quality could actually lead to significant run off issues for National Highways infrastructure ( the Patcham Interchange) and this is demonstrated and proven below.
It is agreed that a development of this scale is likely to generate large amounts of storm water runoff and the below evidence has already been provided which shows that the attenuation provided is insufficient. However it appears it must be provided again as no additional attenuation nor changes have been made to the proposal and this very serious issue still exists. It is not good enough for changes of this nature to occur after the decision has been made, nor to be conditioned. They should and could be determined now as per NPPF 56.
NPPF 56 states "Planning conditions should be kept to a minimum and only imposed where they are necessary, relevant to planning and to the development to be permitted, enforceable, precise and reasonable in all other respects. Agreeing conditions early 16 is beneficial to all parties involved in the process and can speed up decision making. Conditions that are required to be discharged before development commences should be avoided, unless there is a clear justification."
The significant surface water is accounted for with the attenuation by utilising 1/100 year storms + climate change recommendations, but the rates at which it has been agreed to be released due to it’s serious and prolonged impacts on the recognised groundwater flooding zone (the conservation area in the village) mean that taking a single rainfall event as the measure of safe future use is incompetent modelling. The Royal Mail’s Flood Risk assessment also shows overtopping in their modelling scenarios at the end of the attached above document.
However the modelling provided never takes account of the fact that there will be large periods of time when the attenuation is not empty, and in fact the modelling that we have produced shows it will be regularly a quarter-to-half full during the winter peak rainfall months due to reasonable rainfall and the release rate limit. This leads to an insufficient amount of attenuation and will mean an increased likeliness that the proposed development will discharge surface water onto the Patcham Interchange, National Highways infrastructure.
As can be shown in the rain event attached from April 2016, approximately 500 tonnes of surface water would have been escaping from the proposed development over 4 hours had it existed in it’s current form on this date. This would significantly overwhelm the highways sewer due to the amount, and enter the road network. This is just one rainfall event, there will be others in the past and again in the future. This modelled rainfall event assumes the attenuation is empty and has a full available capacity, this will not often be the case.
On this basis please re-review this application for it’s legality relating to National Highways prohibition of the release of surface water onto their infrastructure (the Patcham Interchange) and ask Royal Mail to provide better solutions to ensure this serious issue.
2. Increased Flood Risk to Patcham Village Residents & Conservation Area
There is also the unaddressed issue that during the winter months (October - April) Patcham Old London Road (and the London Road north of the village) are susceptible to groundwater flooding. We have previously reported the levels of this groundwater flooding and demonstrated that for 5 out of the last 8 years the sewer infrastructure on the Old London Road has experienced infrastructure flooding (as per your own definition). This situation is worsening and there is a proven trend from data over the last forty years that the levels groundwater is reaching are coming increasingly closer to the surface regularly.
This means that any additional flows of water have no route through Patcham, Preston Park and into the town during peak groundwater periods, as the sewers in Patcham Village are inundated with groundwater. Therefore the site discharge will cause the sewer flooding to be elongated and more severe due to the constant flows of foul and surface water from the proposed development. Any overtopping (as per the instance described above) could cause this situation to be further worsened and the council has a legal responsibility for ground and surface water flooding.
To rely on Southern Water’s agreement that there is capacity is dangerous, and an attempt to shirk the actual responsibility that the city council has. Southern Water have no obligation to the sewer capacity other than for foul drainage and indeed in a letter received by Cllr Alistair McNair (attached with permission) they state they are not statutory consultees at all.
The letter confirms “Our sewers are built to nationally agreed standards which provide for good levels of protection from flooding. However, the sewers are designed to cope with foul wastewater only”.
They also state "However, in this connection, our investigations indicate that Southern Water can facilitate surface water run off disposal to service the proposed development but the flow from the new development should be no greater than existing discharges to ensure that there is no increase in flood risk”.
There is no existing discharges from the site in its current use as they have no requirement for water use or disposal. Where Southern Water state that the flow that they can facilitate should be no greater than the existing discharges, they are clearly inferring that the proposed discharges cannot be guaranteed against increasing flood risk to downstream infrastructure.
The council are using Southern Water’s agreement to assume that the council’s responsibility in regards to groundwater and surface water disposal will be acceptable and is of a safe rate but this letter shows that Southern Water do not necessarily agree with this and are voicing their concerns.
We point again to the NPPF point 173 “When determining any planning applications, local planning authorities should ensure that flood risk is not increased elsewhere”.
You cannot, and have not satisfactorily proved this point, it is unacceptable for it to be conditioned in its current form because the conditions do not satisfy this point in the framework.
We therefore we must assume that you consider the Royal Mail depot worth more than the conservation and heritage area, and the welfare of the residents of this village.
It is not only the financial burden to them that you consider acceptable but also the impacts on mental health, wellbeing and stress that the increased flood risk from the development of this depot will bring.
This document and evidence has been prepared by the Patcham and Hollingbury Conservation Association, a qualified Mathematician, and a former Brighton & Hove Council Drainage Engineer. They are also consultees to the land north of the bypass (part of the South Downs National Park) and this should also be logged as an official objection from them.
