Planning permission for a farm reservoir or irrigation lagoon

Farm reservoir planning permission is often the easiest of the consents you need. On a holding of five hectares or more, excavations and engineering operations reasonably necessary for agriculture can fall within agricultural permitted development, subject to prior notification. What sits above that is harder: reservoir safety legislation once the stored volume passes a statutory threshold, an abstraction licence to fill it, and possibly an impoundment licence if you are damming a watercourse.

Decide the capacity first and consciously. It drives every other consent in the project.

Agricultural permitted development and the limits on excavation

Part 6 of Schedule 2 to the General Permitted Development Order 2015 gives agricultural rights, and it splits by holding size. On an agricultural unit of five hectares or more, excavations and engineering operations reasonably necessary for agriculture within that unit are permitted, subject to limits and conditions. On units between 0.4 and 5 hectares the rights are narrower and do not extend in the same way to new excavation.

Three points decide most cases.

Reasonably necessary for agriculture is a real test, not a formality. Irrigation storage for a cropping enterprise on the holding will usually meet it. Storage for a neighbouring holding, for a contracting business, or for a use that is really amenity or fishing, will not. Where the water will be sold or used off the unit, permitted development is the wrong route.

Prior notification is required. For an excavation or a deposit, you notify the council and it decides within the prescribed period whether its prior approval is required for the siting of the works. Start without notifying, or start before the council has responded within the period, and the development is unauthorised.

And the rights are curtailed on designated land and near roads, and they are subject to conditions about restoration and about the relationship to dwellings.

Where any of that does not work, a full planning application is the route, and for a large reservoir it is often simpler anyway because the council will want to condition landscape and traffic matters that prior approval cannot reach. The same choice arises with a slurry store or lagoon, where the structure is smaller but the regulatory stack is similar.

Where the area of the works exceeds one hectare, the scheme falls into the category of water management projects for agriculture in the environmental impact assessment regulations, and a screening opinion should be requested. That is a threshold for screening, not an automatic requirement for an environmental statement.

Capacity thresholds and reservoir safety legislation

The Reservoirs Act 1975 regulates large raised reservoirs, meaning those capable of holding a volume of water above the natural level of the adjoining land. The threshold has historically been set at 25,000 cubic metres, and the Flood and Water Management Act 2010 provided for a lower threshold in England. Check the current threshold and the registration requirements with the environment regulator before you fix a design capacity, because the difference in obligations either side of the line is substantial.

Above the threshold, the consequences are ongoing rather than one-off. The reservoir must be registered. Design and construction must be supervised by an engineer from the appropriate statutory panel. There is a continuing regime of supervision, periodic inspection and recording, and the undertaker carries statutory duties. None of that is unmanageable, but it is a permanent cost line that a farm business should decide to take on deliberately.

Below the threshold, the engineering still matters. A bund failure floods land and possibly property downstream, and the liability is the owner's regardless of whether the statute applies.

Note that the measure is water held above natural ground level. A reservoir formed largely by excavation, with a low perimeter bund, can hold a large volume while remaining below the statutory threshold. That is the single most useful design lever available, and it is why the balance between cut and fill deserves engineering input early.

Abstraction licensing for winter filling

Filling a reservoir means taking water from somewhere, and in almost all cases that requires an abstraction licence from the environment regulator.

The general position is that abstraction above a low daily volume requires a licence, and that previously exempt agricultural uses, including trickle irrigation, were brought into the licensing regime. Winter storage is the usual model: abstract from a watercourse or borehole during the high flow period, typically from late autumn to early spring, store it, and use it through the growing season.

Three things shape whether a licence is available.

Catchment availability. Many catchments are already fully licensed or over-abstracted, and no new consumptive licence will be granted. The regulator publishes abstraction licensing strategies by catchment, and reading yours before you commission a design is the cheapest hour in the project.

Hands-off flow conditions. A winter licence is normally conditioned so that abstraction stops when flow in the source falls below a stated level. That affects how reliably you can fill in a dry winter, which in turn affects the storage volume you need.

Impoundment. If the scheme involves damming or diverting a watercourse rather than pumping from it, an impoundment licence is required as well, and the ecological assessment for that is more demanding than for a simple intake.

Apply for the licence in parallel with the planning route. A permission for a reservoir you cannot fill is worth nothing.

Flood risk, dam design and spillways

Where the works are in or near a main river or a flood defence, a flood risk activity permit is needed on top of everything else.

The planning application will need a Flood Risk Assessment dealing with the reservoir as both a receptor and a source. As a receptor, whether the site floods. As a source, what happens if the embankment is overtopped or breached, where that water goes and what it reaches. Councils and the regulator both ask for the breach scenario on anything of size.

The spillway is the detail most often under-designed. It has to pass the design flood without eroding the crest, discharge to somewhere that can take the flow, and remain functional when partly blocked by vegetation or ice. Specify it, do not leave it to the contractor.

Liner choice also has planning consequences. A synthetic liner is visible at the waterline when levels draw down in August, which is exactly when the reservoir is most visible and most used.

Landscape impact of bunds and liners

A reservoir is a large flat object with a raised edge in open countryside, and the bund is usually the thing that draws objection rather than the water.

What helps: keeping the crest low by taking more of the volume in excavation, grading the outer face at a shallow angle so it reads as landform rather than embankment, using local topography to sit the structure in a fold rather than on a skyline, and planting the outer face with species that match the local hedge and copse pattern rather than a conifer screen.

In a National Landscape or a National Park, expect a Landscape and Visual Impact Assessment and expect the design to be revised at least once. Elsewhere a shorter landscape appraisal with viewpoints from public roads and rights of way is usually enough.

Access tracks and the pump house matter more than people expect. A permanent hardstanding, a kiosk and a length of new track can have more visual effect than the reservoir, and they are easy to design better.

Ecology, including newts in nearby ponds

A new water body changes the ecology of a holding, sometimes for the better. The risk sits in what you dig up and what you drain.

Great crested newts are the recurring issue where field ponds exist within a few hundred metres. Survey seasons are narrow, so establishing early whether a survey is needed protects the programme. District level licensing schemes offer an alternative to bespoke survey and mitigation in many areas, and they can be faster.

Other constraints to check at the outset: breeding birds in hedges and scrub to be removed, badger setts in banks, water vole on the source watercourse, and the effect of reduced winter flow downstream on the ecology of the source itself, which the regulator will assess as part of the licence.

Where the reservoir replaces species-rich grassland or affects best and most versatile agricultural land, that is a separate planning consideration and should be addressed rather than left for a consultee to raise.

Conditions, construction traffic and spoil

The excavation produces a large volume of material and what you do with it is a planning matter in its own right.

Spreading spoil across adjoining fields is an engineering operation and can itself need permission or notification, and raising land levels over a wide area is frequently more contentious than the reservoir. Exporting it makes it waste, with duty of care and carrier obligations attached. Using it in the bund is almost always the right answer, and it is another reason to design cut and fill together.

Construction traffic on rural lanes generates most of the local objection on these schemes. A Construction Traffic Management Plan setting out routes, hours, wheel washing and a condition survey of the lane answers the point before it is made.

Expect conditions on construction hours, restoration of any temporary compound, landscape planting with a replacement clause, and in some cases a requirement that the water is used only on the holding. That last one is worth reading carefully if you have any thought of diversifying later.

This is general guidance, not legal advice. Reservoir safety thresholds, abstraction availability and permitted development rights all vary and change, so check the position with your local planning authority, the environment regulator and a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Enter your postcode on PlanScope to see which reports a scheme like this is likely to need.