What does it take to build a new reservoir in the UK

As climate pressures grow and demand for secure water supplies continues to rise, the UK is once again looking at reservoirs as a critical part of long-term water resilience – something we’ve talked about regularly on the Everflow blog. 

But while a reservoir may appear, from the outside, as simply a large body of water, the process of creating one is anything but simple. Building a reservoir is one of the most complex infrastructure projects for a country like the UK and it take years of planning before a spade can break ground. 

Let’s take a closer look at some of the planning, engineering, environmental and community considerations that shape reservoir construction projects.

Finding the right location

Choosing a suitable site is one of the most challenging early steps, particularly in parts of a country that have a relatively high population density and limited space. Engineers, hydrologists and geologists (among others) must assess:

• Topography – is the landscape suited for water storage?
• Geological stability – can the land safely support a dam?
• Proximity to existing water networks
• Potential flood risks
• Land use – agriculture, housing, heritage sites or protected habitats

Over the course of this process, a team of experts may consider dozens of locations before a preferred option is selected.

Environmental impact assessments

It goes without saying that the construction of a reservoir dramatically reshapes the local landscape, which means environmental considerations are extensive. Detailed studies typically look at:

• Effects on wildlife and protected species
• Carbon impact of construction
• Changes to local rivers and groundwater
• Loss of woodland or farmland
• Opportunities for biodiversity net gain
• Demolition of homes and business premises

Modern reservoir projects often aim not just to minimise harm, but to enhance the surrounding environment with new wetlands, woodland and recreational areas.

Community consultation

Local communities play a major role in reservoir planning. A proposed reservoir can affect:

• Homes and farmland
• Footpaths and transport routes
• Local businesses
• Cultural or heritage sites

Consultations, exhibitions, public meetings and feedback processes help shape the final design. In many cases, community improvements such as footpaths, cycle routes or new natural habitats are included as part of the project to drive a positive impact that compensates for any negative consequences of the new reservoir.

Engineering design and modelling

Once a site is approved, the real fun begins and the emphasis falls on engineering solutions. This includes:

• Designing the dam (earth embankment, concrete, or hybrid)
• Modelling water flows and storage capacity
• Planning spillways and flood-control systems
• Designing pipelines, treatment works and pumping stations
• Ensuring resilience against extreme weather and seismic activity

Every aspect must meet stringent safety and regulatory standards in order to maximise the efficiency of the reservoir and minimise the risk of a disaster. This is no easy task, of course. In the case of the proposed new reservoir in Oxfordshire, the reservoir must be capable of safely storing in excess of 150 billion litres of water.

Securing permissions and funding

A reservoir is classed as a nationally significant infrastructure project. This means developers must secure development consent orders (DCOs), environmental permits, land agreements and long-term financing. This stage alone can take several years.

Construction

Actual construction typically spans 5–10 years, depending on size and complexity. Work includes:

• Diverting existing waterways
• Excavation and earthworks
• Building the dam structure
• Installing pipelines and pumping systems
• Constructing new treatment facilities
• Landscaping and reinstating habitats

Reservoir sites often involve hundreds of workers, heavy machinery and round-the-clock logistics. If approved, the Abingdon dam is expected to come online in 2040.

Filling the reservoir

Once complete, a reservoir isn’t filled overnight. It can take months or even years for water levels to reach full capacity, depending on rainfall and inflow rates. During this time, engineers perform safety checks and monitor the dam’s integrity and hydrological stability, as well as water quality and ecological responses.

Only once the reservoir is stable and certified does it become part of the active water network.

Most reservoirs operate for 100+ years, making them one of the longest-serving forms of national infrastructure. So, getting things right from the outset is critical to ensuring that this huge undertaking benefits the community and the country for generations to come.