Mersey barrage scheme

Harnessing tidal power across the Mersey is not a new idea, but the Liverpool Combined Authority is now considering concepts for a tidal barrage across its shores. While it would provide a source of renewable energy to help power the area as an alternative to fossil fuels, the scheme risks damage and possible destruction of internationally important wildlife sites.

What is a tidal barrage?

A tidal barrage involves a dam-like structure that can be built across the mouth of an estuary.

During low tide, the gates of the barrage are open, allowing water to pass through. At high tide, the gates are shut, creating a temporary lagoon. Once the tide has subsided on the seabound side, the gates open again and the force of the water passing through the turbines generates electricity.

Controlling and changing the tide has significant environmental impacts because it disrupts the natural tidal cycle in the surrounding land. The mudflats and saltmarshes that characterise the estuary depend on the tides. At high tide, they are submerged and at low tide they are exposed to create a feeding zone rich in life. Any interference with the tides (i.e. changes in water level, sediment loads, and salinity) risks the disruption of the delicate balance that creates these sensitive habitats, which cannot be replaced.

Why is the Mersey Estuary so important?

The Mersey Estuary is a complex habitat of tidal mudflats, saltmarshes and rocky shores which is home to rare species of plants and animals and supports tens of thousands of birds.

The Mersey Estuary is internationally protected because it sits on a major migration route for birds that come from around the world. During spring and autumn, many bird populations from Europe, Canada and Siberia flock to the shores of the Mersey as they seek out their preferred climate and feed on the worms, shrimps and shellfish.

In 1971 a worldwide UNESCO treaty to protect the sensitive wetland habitats of the world was signed by 169 countries. The Mersey Estuary is one of the sites that was given protection.

The estuary is internationally important (supports at least 1% of the European population) for 6 bird species:

common shelduck (4.2%)
black-tailed godwit (5.7%
common redshank (2.6%)
Eurasian teal (2.6%)
northern pintail (2%)
dunlin (3.6%)

The estuary is nationally important (at least 1% of the UK population) for 5 bird species:

ringed plover (1.3%)
Eurasian curlew (1.3%)
spotted redshank (2.2%)
common greenshank (1%)
Eurasian wigeon (2%)

For these reasons, the estuary also receives additional protection on a European level as a Special Protection Area and nationally through several Special Sites of Scientific Interest.

Sustainable development

Cheshire Wildlife Trust is supportive of renewable energy projects if they are sustainable. Sustainability is not just about net zero, it is also about considering the full impact of a project on the natural environment, including the wildlife. Potentially irreversible changes caused by the construction of a poorly designed barrage, such as the design that was put on hold in 2011, could put at risk this incredibly important ecosystem and the survival of the species that rely on it.

The leaders of the United Nations agreed what sustainable development looks like and created the 2030 Sustainable Development Goals. If a development breaches a goal, then it is not considered sustainable. While a barrage across the Mersey might meet the clean energy, climate and infrastructure goals, it would almost certainly breach the two biodiversity goals relating to life on lands and in water.

Breached: Goal 14 Life Below Water - conserve and sustainably use the oceans, seas and marine resources for sustainable development.
Breached: Goal 15 Life on Land - protect, restore and promote sustainable use of land ecosystems, and halt and reverse land degradation and halt biodiversity loss.
Met: Goal 7 - affordable clean energy: - ensure access to affordable, reliable, sustainable and modern energy for all.
Met: Goal 9 - Industry, infrastructure and innovation: - Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation
Met: Goal 13 climate action - take urgent action to combat climate change and its impacts