Reservoirs and irrigation storage on farms

A farm irrigation reservoir almost always needs planning permission. The agricultural permitted development rights in Part 6 of the General Permitted Development Order 2015 cover excavations and engineering operations reasonably necessary for agriculture, but they cap the ground area of the works, and a reservoir holding enough water to irrigate a commercial cropping rotation will exceed that cap comfortably. So farm reservoir planning permission is a full application, with a design and access statement, landscape work and usually archaeology.

The good news is that these schemes are approved regularly. The applications that fail are the ones that treat the reservoir as an engineering drawing with a planning form attached.

Whether the right covers it

Part 6 Class A applies to agricultural units of five hectares or more and permits works reasonably necessary for the purposes of agriculture within that unit. Two limits do the damage. The ground area covered by any building, structure or works is capped, and separate schemes cannot be salami sliced to stay under it. Excavations and engineering operations also need prior approval for siting, design and external appearance where the relevant conditions apply.

Part 6 Class B, which covers units between 0.4 and five hectares, is narrower still and will not deliver a reservoir.

Where the works sit on a National Landscape, a National Park, a conservation area or a World Heritage Site, the rights are reduced further. And on land near a scheduled monument, works can require separate scheduled monument consent regardless of the planning position. A lawful development certificate is the only formal way to confirm that anything you intend to build under Part 6 is lawful.

The reservoir safety regime

The Reservoirs Act 1975 regulates large raised reservoirs, which are those holding a volume above the statutory threshold above the natural level of the adjoining land. The Flood and Water Management Act 2010 changed the way that threshold and the risk designation work in England, so check the current registration duty and volume figure with the Environment Agency before you fix the design. Reservoirs caught by the regime need a panel engineer for design, construction and supervision, and the undertaker has continuing duties on inspection and record keeping.

This sits alongside planning rather than inside it. The planning officer will not enforce reservoir safety, and the Environment Agency will not grant planning permission. Both have to be satisfied, and the engineer's design is what reconciles the two.

Abstraction, winter fill and licensing

Most irrigation reservoirs are filled in winter from a watercourse or a borehole under an abstraction licence issued by the Environment Agency under the Water Resources Act 1991. Winter fill licences are typically conditioned to periods of higher flow, with daily and annual volume limits and a hands off flow below which abstraction must stop.

Two practical points. A licence application runs on its own timetable and its own evidence, and the two applications should run in parallel rather than in sequence. And the reservoir volume should be justified by the cropped area and the irrigation need, because a planning statement that cannot explain why the reservoir is the size it is invites the objection that the scheme is really a commercial water trading operation.

Landscape, soils and archaeology

A reservoir is an earthworks project. The bund is the visible part, and on flat arable land a bund of three or four metres reads as a landform that was not there before. Expect the landscape officer to ask for:

• Cross sections showing the bund profile against existing ground levels.
• A cut and fill balance, because importing or exporting material changes the traffic case.
• Photomontages or wireline views from public rights of way and nearby dwellings.
• A planting strategy that works with the local landscape character rather than screening with a conifer belt.

Where effects extend beyond the immediate holding, a Landscape and Visual Impact Assessment prepared to the third edition of the landscape guidelines is the document to produce. On best and most versatile land, the authority will also want to understand the soil resource, and an Agricultural Land Classification survey carried out by a soil scientist is the evidence base for that.

Archaeology is the risk most often underestimated. A reservoir excavation removes everything below ground across a large footprint, so county archaeologists routinely ask for a desk-based assessment followed by trial trenching, secured by condition. Deal with it early. A trenching programme discovered at determination stage costs a season.

Ecology and the habitat a reservoir creates

New water bodies attract great crested newts, and existing ponds within the zone of influence need assessment before work starts. Survey windows are narrow. Environmental DNA sampling runs between mid-April and the end of June, and trapping seasons are shorter still, so a scheme that decides in July to check for newts waits until the following spring.

The reservoir itself can be a biodiversity benefit. Shallow margins, a drawdown zone and a graded bank deliver more habitat than a steep sided tank, and the statutory biodiversity metric will recognise that. A Preliminary Ecological Appraisal at the start tells you which of these questions apply. Protected species work and biodiversity net gain calculations require a suitably licensed ecologist and a competent person under the Environment Act 2021 regime, and an AI-assisted draft is a starting point for that professional rather than a substitute for them.

Tracks, pumps and pipelines

The reservoir is rarely the whole application. Access for construction traffic, a permanent maintenance track, a pump house, a control kiosk, buried mains out to the fields and a power supply all need to appear on the submitted plans. Leaving them out and applying later reads as fragmentation.

Pumps run at night during the irrigation season. Where a dwelling sits within earshot, expect environmental health to ask about plant noise, and a modest acoustic enclosure specified at design stage costs far less than a retrofit after a complaint. Existing farm tracks and new accesses have their own rules, and a track that is properly agricultural may be covered by Part 6 even where the reservoir is not.

Conditions to expect

Authorities commonly attach conditions covering construction hours, a haulage routing plan, wheel washing, the finished bund profile and levels, a landscape management plan with a five or ten year establishment period, archaeological watching briefs, and restoration if the reservoir is decommissioned. Read them before you accept them. A condition requiring all imported material to be certified is straightforward on a cut and fill balanced scheme and expensive on one that relies on imported clay.

Read the landscape management condition with particular care. Establishment periods of five or ten years bind a successor in title, and the planting schedule attached to the permission is the one that will be checked on a monitoring visit. Where the reservoir replaces an existing abstraction arrangement, say so in the supporting statement, because a scheme that reduces summer abstraction pressure on a watercourse carries a benefit the Environment Agency will support.

Write the application as an integrated case: water need, engineering, landscape, soils, heritage, ecology and traffic, in that order. Enter your postcode on PlanScope to see which reports the site is likely to need before you commission anything.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.