Bericote Properties appointed Hydrock’s flood risk team to provide critical support to secure planning approval for the development of an industrial/warehouse site comprising of three commercial units within the strategic Alpha Park site, part of Chandler's Ford Industrial Estate which is one of the key industrial / distribution locations in Southampton.
Alpha Park operates 24/7 hours and offers a secured service yard, clear height of 12m and Grade A offices.
As a consequence of the proposed 24 hour site operation with an existing residential development to the north of the site, the location of the three new commercial units could only be along the bank of an adjacent watercourse within areas classified as being at high risk from fluvial flooding (Flood Zone 3).
To enable Bericote to gain planning approval, Hydrock’s flood risk engineers were appointed to demonstrate that the scheme could fully meet the requirements of the National Planning Policy Framework (NPPF).
To address the flood risk issues, we undertook a detailed hydrological and hydraulic modelling study to confirm the existing risk. This exercise provided a detailed understanding of the flood mechanisms operating within the area.
The modelling confirmed that the northern section of the site and two of the proposed units were located within the high risk flood zone. As such, the proposals would result in the loss of floodplain storage and would be contrary to policy requirements due to the increased risk of flooding.
Given the identified loss of floodplain, compensatory storage was needed. Owing to the inflexibility of other constraints (particularly noise and lighting), space for any flood risk mitigation was very limited. Following discussions with the wider design team we advocated rotating one of the units to provide an area that could be used for compensatory flood storage in the north eastern corner of the site as well as functioning as a staff car park area.
The principles of lowering this car parking area to provide the required storage was discussed and agreed with the Environment Agency (EA) subject to detailed modelling. Hydrock demonstrated that there would be no detrimental impact on flood risk elsewhere and in line with the requirements of NPPF.
Whilst our modelling confirmed that suitable compensatory floodplain storage was available, the levels required to do this necessitated site level changes that meant access to the neighbouring unit needed to be altered from level access to dock loading bays. This was discussed and agreed with the architect and client as being a workable solution.
The hydrological and hydraulic modelling confirmed a suitable site layout that ensured both the client’s and end users’ needs were met, whilst also fully addressing the site constraints in line with planning policy. This resulted in the EA removing their objection on flood risk grounds, unlocking the site for development with the approval of planning permission.