Planning permission for a farm reservoir or irrigation pond
Most irrigation reservoirs need full planning permission because excavating a basin is an engineering operation. Here is how the permitted development limits, reservoir safety thresholds and abstraction licensing fit together.
A farm reservoir almost always needs planning permission, because excavating a basin and raising banks is an engineering operation under section 55 of the Town and Country Planning Act 1990. The exception is the narrow one in the agricultural permitted development rules, and it only helps holdings of five hectares or more. Before any of that matters, three separate regulators may have an interest in the same hole in the ground: the local planning authority for the development, the Environment Agency for the water you put in it, and again the Environment Agency for reservoir safety if the volume is large enough.
Farm reservoir planning goes wrong when an owner treats it as a drainage job rather than a development. The digger arrives, the bund goes up, and the first letter comes from enforcement.
Why a reservoir counts as development
Section 55 defines development as building, engineering, mining or other operations in, on, over or under land, or a material change of use. Cutting a basin, forming an embankment and laying a liner are engineering operations on any ordinary reading. The use of the land also changes in substance if a grazing field becomes a water body, although in practice the operations point is the one that decides it.
Two situations muddy this. Scraping out an existing silted pond to its original profile can be maintenance rather than development, provided the footprint and depth are not enlarged. And a temporary lagoon for slurry or silage effluent sits in a different part of the permitted development order from an irrigation store. Neither exception stretches to a new winter-fill reservoir of several thousand cubic metres.
If you want certainty rather than an opinion, apply for a lawful development certificate under section 191 or 192 of the 1990 Act. It is the only formal route to confirming that works are lawful without permission.
What agricultural permitted development actually allows
Part 6 of Schedule 2 to the General Permitted Development Order 2015 splits agricultural rights by holding size. Class A covers agricultural units of five hectares or more and does extend to excavations and engineering operations reasonably necessary for agriculture within that unit. Class B, for units between 0.4 and five hectares, is much thinner and does not give you an excavation right at all.
Class A carries limits that catch reservoirs regularly:
- the ground area covered by the excavation or deposit, together with any other works or structures within 90 metres, must not exceed 465 m²
- no part of the works may be within 25 metres of the metalled surface of a trunk or classified road
- the works must be reasonably necessary for the purposes of agriculture within that unit, which is a test about farming need, not about convenience
A 465 m² ceiling is roughly a 21 metre square. Any reservoir worth building for irrigation is larger than that, so most schemes fall outside Class A on area alone.
Where Class A does apply, it is not a free pass. The applicant must first apply to the council for a determination as to whether prior approval is required for the siting of the excavation or deposit. The authority has 28 days to respond, and it can require details before work starts. Get that wrong and the works are unauthorised even though the right existed.
Capacity thresholds under reservoir legislation
The Reservoirs Act 1975 regulates large raised reservoirs, meaning structures designed to hold water above the natural level of the surrounding land. The Flood and Water Management Act 2010 amended the regime in England to lower the capacity threshold from 25,000 m³ to 10,000 m³ and to introduce risk designation, with the Environment Agency as enforcement authority. Reservoirs at or above the threshold must be registered, and those designated high-risk must be supervised and inspected by panel engineers appointed under the Act.
These provisions were brought into force in stages, so check the current position with the Environment Agency rather than relying on a figure in a trade article. The design consequence is blunt: a reservoir sized just under the threshold avoids a supervision regime that adds a permanent professional cost, and many farm schemes are deliberately built to sit below it.
| Capacity above natural ground level | Typical regulatory consequence |
|---|---|
| Under the registration threshold | Planning permission still needed, no reservoir safety registration |
| At or above the threshold | Registration with the Environment Agency, risk designation, engineer supervision where high-risk |
Treat that table as a prompt to check, not as the rule itself. The safety regime turns on water stored above natural ground level, which means a reservoir dug largely below ground can hold a big volume without crossing the line.
Filling it lawfully: abstraction and impoundment
Water is regulated separately from land. Under the Water Resources Act 1991 you need an abstraction licence from the Environment Agency to take more than 20 m³ a day from a river, stream or borehole. Winter filling is the normal pattern for irrigation reservoirs, and winter licences are easier to obtain than summer ones in catchments already under pressure, though in some catchments no new licence is available at all.
Building a dam or weir across a watercourse to create the storage needs an impounding licence as well. Rainwater harvested from your own roofs and yards, or collected as surface run-off within the holding, avoids the abstraction question but rarely fills a reservoir on its own.
Sequence matters here. An owner who obtains planning permission and then discovers the catchment is closed to new abstraction has bought an expensive dry basin. Ask the Environment Agency about water availability before the planning application, and say plainly in the Planning Statement what the water source is and what licence position applies.
Landscape, ecology and the material you dig out
Bunds are the part that gets refused. A reservoir formed by raising banks two or three metres above a flat field reads as a new landform for miles, and the reflective sheet of a liner or the exposed clay face reads worse. On sites in or near a National Landscape or a National Park, expect the authority to ask for a Landscape and Visual Impact Assessment prepared to the third edition of the GLVIA guidelines. Profiling the bund with shallow gradients, tying it into existing hedge lines and planting the outer face early does more for the case than any paragraph of policy argument.
Ecology cuts both ways. A new water body can be a genuine gain for amphibians and invertebrates, and a well-designed reservoir with a shallow margin and a wildlife bay is an easy story to tell. But the works may affect great crested newts, water voles or nesting birds, and survey seasons are unforgiving. Newt eDNA sampling runs from mid-April to the end of June, water vole surveys from April to September. Miss those windows and the scheme slips a year.
Since the Environment Act 2021 regime came into force, most planning permissions carry the biodiversity gain condition requiring a ten per cent uplift secured for 30 years. A Biodiversity Net Gain Assessment using the statutory metric has to be completed by a competent person, and the biodiversity gain plan has to be approved by the authority before development starts. Permitted development under the GPDO sits outside that condition, which is one more reason to know which route you are on.
Then there is the spoil. A hectare-scale reservoir generates thousands of cubic metres of subsoil, and where it goes is a planning question and often a waste question. Spreading it to raise low ground is engineering operations in its own right. Check with the Environment Agency whether a permit or an exemption is needed before assuming the material can simply be pushed into the next field.
Making the application
For anything beyond a small farm pond, the application is a full planning application to the local planning authority. A workable pack usually contains a location plan and site plan, existing and proposed sections through the basin and bund, a design statement, a Planning Statement setting out the agricultural need, an ecology report, a landscape assessment where the site is sensitive, and a construction access plan.
The agricultural justification carries real weight. Write it with numbers: the cropped area served, the irrigation demand across a dry season, the current water source and why it is insufficient. An authority that can see a farming need behind the earthworks is looking for a way to say yes.
Illustrative example: a 40-hectare holding growing salad crops proposes a 45,000 m³ winter-fill reservoir with a maximum bank height of 2.5 metres above field level. The area is well over the 465 m² permitted development ceiling, so a full application follows. The stored volume above natural ground level is modest because the basin is dug deep, which changes the reservoir safety analysis. The case officer consults the lead local flood authority on the outfall and the county ecologist on the newt evidence. Figures here are illustrative only.
Determination is normally eight weeks for a minor application, longer where consultees need more time. If the site is in a National Landscape, budget for a committee report rather than a delegated decision, and ask about pre-application advice before you draw anything.
This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and use a lawful development certificate if you need certainty about permitted development.
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Frequently asked questions
Do I need planning permission to dig an irrigation reservoir?
Almost always, yes. Excavating a basin and forming banks is an engineering operation under section 55 of the Town and Country Planning Act 1990. Agricultural permitted development under Part 6 Class A of the GPDO 2015 can cover excavations on holdings of five hectares or more, but only where the ground area covered stays within 465 square metres, which rules out most working reservoirs.
What capacity triggers the Reservoirs Act 1975?
The Act regulates large raised reservoirs, which store water above the natural level of the surrounding land. The Flood and Water Management Act 2010 lowered the English threshold from 25,000 to 10,000 cubic metres and added risk designation, with staged commencement. Because a deep basin stores less above ground level, design can affect whether registration applies. Confirm the current threshold with the Environment Agency.
Do I need an abstraction licence to fill the reservoir?
You need a licence from the Environment Agency to abstract more than 20 cubic metres a day from a river, stream or borehole. Winter filling is the usual pattern and is easier to licence than summer abstraction, but some catchments are closed to new licences entirely. Damming a watercourse also needs an impounding licence. Ask about water availability before applying for planning permission.
Does biodiversity net gain apply to a farm reservoir?
If the scheme needs planning permission, the biodiversity gain condition introduced by the Environment Act 2021 will normally apply, requiring a ten per cent uplift secured for 30 years and a biodiversity gain plan approved before development starts. The statutory metric must be completed by a competent person. Development carried out under permitted development rights sits outside the condition.
Where can the excavated subsoil go?
Moving several thousand cubic metres of subsoil around the farm is itself an engineering operation and can be a waste matter as well. Raising low ground or forming screening bunds should be shown on the application drawings and justified. Check with the Environment Agency whether a permit or a registered exemption is needed before the material is spread.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.