Flood Risk Assessment Case Study: Grantham, Lincolnshire

Installation of a Solar Farm on Land at The Grange, Ingoldsby, Grantham, Lincolnshire, NG33 4EY

OVERVIEW
A planning application was made to erect a 49.5MW solar panel farm with power inverter stations, security fencing, access gates and CCTV security cameras at The Grange, Grantham, Lincolnshire, on a site of more than 100 hectares.

Premier Water Solutions Ltd (PWS) was appointed by Padero Solar Renewables to prepare an assessment to accompany the planning application.

PWS reviewed the existing information, undertook a site visit and provided the necessary technical calculations, drawings, and report in order to provide sufficient information for review by the local authority

PROPOSAL
It was proposed to erect 223,008 solar panels. There will be inverter and transformer buildings with a substation.

Surface water falling on the buildings to drain onto the surrounding ground. The floor level of the building to be raised to ensure that the base of the inverter is above any potential overland flow.
An access road is to be constructed using a permeable finish as not to contribute to surface water runoff. The inverter buildings will generate runoff. It is proposed that this water be drained via downpipes and allowed to sheet off and infiltrate the surrounding ground.

CONCLUSIONS

Walk over survey provided with photographs

Hydrological and surface water assessment provided

Site is located in flood zone one, low probability of flooding
Interception swale built with reshaping of the existing bank

A swale one metre wide located after every sixth row

No panels to be sited within 10m of marshy ground

Buildings and plinths to drain onto adjacent ground

Access road to require further design to consider the infiltration and structural capabilities of the road

No percolation testing was undertaken as the soils are mostly drained

Site returned back to a grassed surface agricultural field with remedial landscaping and re-seeding

Silt trap placed every 40-50m following the contours of the field to intercept any suspended solids

A construction quality control plan was produced that suggested:

• top soil generated from the construction stored in a protected area.
• silt fences installed
• regular site inspections are necessary
• appropriate storage of oil and hydrocarbons
• oil spillage kit to be located on site
• signed containers to enable separation of waste and to prevent waste from blowing around

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