The following are the most significant constraints faced by the scheme, in broad order of significance (most significant first):
The current condition of the apron and footings of Hexham Bridge
The current bridge over the River Tyne at Hexham was completed sometime between 1793 and 1795. In order to prevent the bridge being swept away or significantly damaged by the river (the fate of previous bridges) the piers were constructed on timber piles and platforms and the whole river bed was framed and sett with horizontal timbers both under the arches, for 1 or 2m upstream and for almost 8m downstream from the ends of the piers. The timber piles must not be disturbed or moved or exposed to the air. This means also that the concrete apron cannot be cut into as part of any engineering work. Any development that takes place at this location must work within these significant constraints.
The current condition of the riverbed at this site
The river bed downstream and upstream of Hexham Bridge was subjected to what has been described as ‘gravel extraction on an industrial and unsustainable scale’ during the mid- and late twentieth century. The extent of commercial gravel extraction is documented in hydrologist David Archer’s book Tyne and Tide (2003) and described by him as “the rape of the Tyne”.
Gravel extraction has lowered and destabilised the river bed. The impact of this commercial gravel extraction on any engineering project at or near Hexham Bridge is hard to over-state.
The large flood range of the River Tyne
The design life of Hexham River Hydro is 120+ years in a river with the one of the highest recorded flood discharge in the UK and a huge variation in levels between lowest and highest flows.
The costs of civil engineering works in any river can escalate, but the conditions on the River Tyne provide a particular challenge, recent evidence being the failures of the cross‐Tyne water supply pipe in 2005 and the sewer pipe in 2010.
The angling lobby
The national and local angling lobbies expressing anti-hydro opinions have been extremely vocal during the detailed feasibility and detailed design phases.
In late 2010 the Hexham River Hydro team identified an inconsistent and conflicting record of ownership of the area of land and river likely to be needed for construction of a hydro scheme on the River Tyne at Hexham Bridge. Northumberland County Council was the majority owner but some land and rights were retained by Allendale Estates and these parties held inconsistent records on the extent and nature of their respective rights.
For more than two years the Hexham River Hydro team sought to broker a resolution of these boundary issues. This included, in 2011 and 2012, using the pro bono support of London lawyers Ashurst to review and summarise all the available historical documentation to articulate as clearly as possible the agreed-upon boundaries and rights and the areas of conflicting or missing information. This documentation was then provided to both Northumberland County Council and Allendale Estates by the Hexham River Hydro team.
Depending on the outcome of negotiations the hydro scheme would either have one landowner (Northumberland County Council) or two (Northumberland County Council and Allendale Estates). Clarification eventually received confirmed the latter.
Whilst the ownership situation remained unresolved, the Hexham River Hydro team engaged proactively with both parties to seek relevant outline permissions.
Considerable expenditure must be made ‘at risk’ for a scheme of this nature i.e. the money must be spent before it can be determined whether or not the scheme can be built. Funding for this type of expenditure is extremely hard to raise.
Expertise and capacity in stakeholder organisations
Successful engagement with stakeholders is a two-way street: it requires skills, capacity, knowledge and engagement from the community hydro development team; and it requires the same from other organisations. Not all stakeholder organisations were willing to engage in this way.
Schemes of this nature rely on volunteer labour, whose capacity is constrained by ’day jobs’ and other crucial commitments.
Hexham River Hydro, an energyshare project made possible by British Gas and supported by Carbon Leapfrog, Cooperative Enterprise Hub, Vattenfall and The Naturesave Trust