Flooding is great concern for this planning application. Two comments already posted on the Somerset Planning website may be of interest …
The objection to this planning application concentrates on aspects of the increased flood risk that the 4.96ha proposed development site presents and references the Flood Risk Assessment (FRA) document produced by Simon Bastone Associates for their client Emily Estates.
Section 10 of the Bastone FRA document, Design For Exceedance, states that the surface water storage capacity has been designed to cope with a 1/100 year rainfall event of 6 hours duration, ie circa 1512m3 of storage capacity (10.2.5). Using the data and calculations in Appendix 1 of the FRA document it can be demonstrated that during the actual rainfall event of May 9th 2023 of 100mm of rainfall in one hour (figures from the LLFA preliminary report on the Yarlington Flood) over the site and surrounding hills, both the capacity of the planned surface water storage onsite and the flow rate of the planned outlet pipe would have been completely overwhelmed.
If the proposed site had existed on May 9th 2023 the surface water runoff from the developed site alone during the hour of intense rainfall would have been 2684m3. Runoff at a maximum allowable greenfield rate of 28l/s down the outflow pipe would still have left 2440m3 of surface water needing to find its level down at the river Cam in Yarlington, way above the site’s planned circa 1512m3 of storage capacity.
The Bastone FRA document contends that the entire development site is in a Flood Zone 1 area so does not need to take into account surface water issues beyond the development site. Consequently their FRA analysis does not include the extra water runoff from the surrounding hills that would flow down to the River Cam because 5ha of grade 1 agricultural land soakaway at the base of Yarlington Sleights will be replaced by 5ha of impermeable concrete and semipermeable surfaces.
According to the table in appendix L of the FRA document existing surface water runoff a 1/100 year 6 hour rainfall event would produce a peak flow rate of 629l/s of surface water coming off the hills, the tolerance level used to design the site with rainfall intensity of 13mm/hr. But we know that on May 9th last year the peak flow rate off the Yarlington Sleights hillside was multiples of this number, with rainfall intensity of 100mm/hr over 33ha, ie a peak flow rate of 4,691l/s.
Section 11 of the Bastone FRA document discusses Residual Risks. 11.1.4 mentions overtopping and geotechnical failure ‘Following very large surface water exceedance events’. Based on the above observations I would argue that the 1/100 year rainfall event already happened in 2023, and the subsequent flooding in Yarlington and downstream along the River Cam would have been even more serious if the site had existed in its proposed form on that date given the above factors. Similar 1/100 year rainfall events happened in the nearby villages three more times last winter as will shortly be detailed in the expected LLFA Section 19 Report.
The strong objection to this planning application based on the the above flood risk factors, and failure to apply a Sequential Test to the proposal, which would clearly demonstrate the existence of more suitable sites for the development in terms of FRA on existing brownfield sites in the Emily Estate’s land portfolio.
This strong objection to this planning application concentrates on the elevated flood risk that the proposed 4.96ha development site presents and references the Flood Risk Assessment (FRA) document produced by Simon Bastone Associates for their client Emily Estates.
The Bastone FRA document starts by stating that the entire development site is located in a Flood Zone 1 area which means that the Flood Risk Assessment is confined to the development site only and does not need to consider the surrounding areas (section 3.3.3). It also states that the application does not need Sequential and Exception Tests (section 7.1.1) as the site is entirely on Flood Zone 1 land. The flood assessment calculations in the document are based on advice received from the Local Lead Flood Authority (LLFA) in letters exchanged in late 2022, and at no point in the available exchange is the scale of the development mentioned.
The FRA document states that all surface water produced on the site will be drained away after various measures off the SE end of the site into the River Cam in Yarlington via a 480m drainage pipe. This pipe outlet is actually in a Flood Zone 3 area that was subject to a catastrophic flood on May 9th 2023. Yarlington, Galhampton, North Cadbury and Queen Camel on the river Cam were all flooded, 166 houses were involved in total on that day and we are currently awaiting the final Section 19 Report from the LLFA on the flood event.
Guidance from the Environment Agency to LPAs published on 15th April 2015 states that:
‘A Sequential Test is required for major development if any proposed building, access and escape route, land-raising or other vulnerable element will be in flood zone 2 or 3, or in flood zone 1 and your SFRA shows it will be at increased risk of flooding during its lifetime.‘
It is surprising that the proposed drainage pipe outlet into the River Cam was not considered part of the planning application’s site given that it is located in Flood Zone 3, and hence should have triggered a Sequential Test for the application.
On the matter of the expected LLFA Section 19 Report See guidance on FRA for planning applications from www.gov.uk, in particular Paragraph: 027 (Reference ID: 7-027-20220825) and I quote:
‘The Sequential Test should be applied to ‘Major’ and ‘Non-major development’ proposed in areas at risk of flooding, but it will not be required where: The site is in an area at low risk from all sources of flooding, unless the Strategic Flood Risk Assessment, or other information, indicates there may be a risk of flooding in the future.‘
The expected LLFA Section 19 Report constitutes material other information.
In addition the Town and Country Planning Procedure (2015) Schedule 4 paras zc states that if a proposed development is in Flood Zone 2 or 3, or Flood Zone 1 with critical drainage issues it should be referred to the Environment Agency. Has this taken place?
So on all the above criteria a Sequential Test should have been undertaken for the application. Applied to this proposed development site the Sequential Test would demonstrate that there are other sites far more suitable for the planned development in the Emily Estate’s existing Farm portfolio in terms of FRA.
Given the May 9th 2023 flood event in Yarlington and the downstream villages on the River Cam and the subsequent ongoing flood consultation and expected Section 19 Report, it feels irresponsible to say the least for the LPA to consider a major non residential development above Yarlington and the River Cam catchment area without applying Sequential Testing, and without taking into account the flood management issues it triggers beyond the boundaries of the proposed development site.
