Greenfield Housing and the Sequential Test
A village of 3,200 people outside a bypass is considering a 400-dwelling development on 12 ha of agricultural land. The site is outside the development zone, grades 1–2 soil, and overlies the main aquifer recharge area. The local road carries 6,500 vehicles/day against a design capacity of 8,000; the primary school is at 95% capacity. A flood study shows the site stores 18,000 m³ of floodwater in a 1-in-50-year event. The developer argues that 35% of the site will be open space, that 80 affordable homes are needed, and that a new spine road will reduce village congestion. The local plan favours brownfield regeneration, but the only brownfield site is a former quarry 3 km away, requiring €4 million remediation and accessible only by country lanes. The Planning Authority must decide whether to grant outline permission. Residents oppose the loss of farmland; the chamber of commerce supports growth. The Environment and Resources Authority has flagged the aquifer and flood risk.
1. Assess the site against three sustainability criteria and explain why the brownfield alternative is not automatically preferable.
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Flood risk: the site stores 18,000 m³ in a 1-in-50-year event; building would displace storage and could increase downstream flooding. Aquifer: the site is a recharge area, so impermeable surfaces would reduce infiltration and raise pollution risk. Transport: the road carries 6,500 of 8,000 design capacity; 400 dwellings could add roughly 2,000–2,400 vehicle trips/day, exceeding capacity, and the school is already at 95%. Soil: grades 1–2 farmland is a finite resource. The brownfield quarry is not automatically preferable: it needs €4 million remediation, is 3 km from the village and is reached by country lanes, which may create new traffic and access problems. However, it uses previously developed land and could be made viable with conditions. The sequential test requires brownfield first unless it is not viable, so the comparison must be on net sustainability, not land type alone.
2. Recommend a planning decision with conditions, or an alternative strategy.
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Refuse outline permission as proposed. The site is outside the development zone, uses best farmland, displaces flood storage and threatens the aquifer, while the road and school are near capacity. Require a sequential test of the quarry site: if remediation and access can be funded, direct the 80 affordable homes there with a bus service and safe walking and cycling links. If the quarry is not viable, consider a smaller scheme of about 150 homes on the least sensitive part of the site, with no building in the 18,000 m³ flood storage area, raised floor levels, permeable surfaces, aquifer monitoring and a school contribution. Conditions should include flood compensation for a 1-in-100-year plus climate-change event, a traffic cap and a travel plan. This recognises housing need but judges this site to be poor.
3. If development proceeds, how should the 18,000 m³ flood storage figure shape the design?
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The 18,000 m³ is the volume stored on the site during a 1-in-50-year event. Development must not reduce that storage, or downstream flooding will increase. Design should keep the storage area as open space, parkland or a detention basin, not as housing. Use sustainable drainage systems, such as permeable paving, swales and green roofs, to slow runoff. Set floor levels above the modelled flood level with freeboard, and model a 1-in-100-year event plus climate change, because the 1-in-50 figure is not a safe design standard. If any storage is lost, compensate on-site or nearby. This protects the village downstream and makes the scheme more resilient.