Clapper and packhorse bridges

Overall vulnerability

Features assessed:

• Clapper bridges
• Packhorse bridges

Special qualities:

• Landscapes that tell a story of thousands of years of people, farming and industry

Feature description:

Clapper bridges are simple footbridges consisting of one or more large slabs of stone placed over a watercourse either directly onto each bank or supported on stone piers. In the PDNP there are a small number of clapper bridges. Examples include two gritstone bridges spanning Barbrook on the Eastern Peak District Moors, two limestone bridges located near Hassop, and impressive gritstone bridges with multiple supports over the River Bradford near Youlgreave.

Packhorse bridges are more advanced structures which were built to allow packhorses carrying goods to cross watercourses. These are slightly more abundant with 15 examples mapped by the PDNPA in locations across the Dark, White and South West Peak. In the PDNP the majority of these bridges date from the 17th, 18th and 19th centuries, although some may be significantly older. Both of these bridge types were historically used as transport infrastructure for trade and hold a high historical value. There are other bridges that are important too – sometimes medieval, that have not been addressed within the scope of this assessment.

How vulnerable are building materials?

Clapper and packhorse bridges in the PDNP have been rated ‘moderate’ on our vulnerability scale. This score is due to a moderate sensitivity and exposure to climate change variables, a variable current condition, and a moderate adaptive capacity.

The impact of changed precipitation regimes are likely to be the most significant for these features. An increase in erosion and the potential for structural damage through attrition or large flooding incidents could be detrimental, making all bridges more vulnerable. While traditional building materials and techniques have displayed a good deal of resistance to date, and it should be possible to repair some damage, irreplaceable historic information may be lost. There are a limited number of these features, and they have limited diversity. Non-designated bridges on privately owned land or not carrying public rights of way will possibly be the most vulnerable of these features as they are often little understood and may have limited monitoring and maintenance.

Current condition

Information about the current condition of packhorse bridges in the PDNP is incomplete, but overall condition appears to be variable. Of the 15 packhorse bridges mapped two have been reconstructed, one is known to have been ruined. Six have listed status and one has been delisted. Some bridges such as the grade II listed example at Three Shires Head are known to have been modified, in that case with the addition of a concrete roadway. Examples of known damage to bridges include the loss of coping stones and nearby surface rutting as a result of four-wheel drive vehicle use at Washgate over the River Dove. It is also known that bridges which take vehicle traffic have been subject to damage from air pollution. Clapper bridge condition information could not be found, but all examples appear to be relatively intact, and at least two are grade II listed.

What are the potential impacts of climate change?

Overall potential impact rating

Sedimentation or erosion

The close relationship of bridges to watercourses means that changes to precipitation will be likely to have the greatest potential impact in these features. Increased winter precipitation will result in higher river levels with consistently increased flow. Damage caused by hydraulic action and scouring by sediment would increase on those part of the structure in contact with water, while banks may be undermined by the same forces. This is likely to accelerate surface damage and also potentially weaken the structural integrity of the bridge over time. Data Certainty: Very Low

An increase in the frequency and intensity of storm events in both winter and summer will have similar effects, and is also likely to increase the incidence of bridges being damaged by sediment or debris washed downstream.

Increased frequency of drought periods in the summer may also compromise the long-term robustness of structures through the cracking of the ground, particularly in clay-heavy areas. Data Certainty: Very Low

Direct impacts of climate change

An increase in the frequency and severity of storm events may result in the increase in direct damage to bridge structures by hydraulic action from precipitations Data Certainty: Very Low although conversely a reduction in freeze-thaw events during warmer winters may slow some damage. Data Certainty: Low

Invasive or other species interactions

Increased annual average temperatures and higher minimum winter temperatures coupled with an increase in atmospheric carbon dioxide and nitrogen are likely to have an impact on plant life. A longer growing season and potential faster rate of growth means that some bridge structures could be damaged, or their structural integrity compromised. This could be caused either by plants growing in stonework or invasive species such as Himalayan balsam undermining the stability of river banks. Data Certainty: Low

Human behaviour change

An increase to visitor and tourist numbers to the PDNP as a result of hotter, drier summers may increase wear and tear and damage from foot and particularly vehicular traffic. An increase in recreational off-road vehicle usage has the potential to cause increased damage to bridges which are on tracks or green lanes. Data Certainty: Very Low

It is also possible that there will be an increase in the building of hard flood defences in places as a result of increased winter precipitation. This can lead to channel water becoming higher before overtopping and therefore increasing hydraulic energy within the channel downstream of defences. Data Certainty: Low

What is the adaptive capacity of building materials?

Overall adaptive capacity rating

The construction of many of these features within the PDNP has proven to be fairly resistant to damage from erosion and weathering, and the survival of many of these bridges for hundreds of years demonstrates a good degree of inherent robustness of traditional building materials and techniques. However the tiny size of some bridges, particularly clapper bridges mean that a large storm event has the potential to be very detrimental. Once damaged, historic information is lost even if the structure itself can be repaired.

There is a fairly low number of packhorse bridges and even fewer clapper bridges in the PDNP and many span the same rivers. There is also limited diversity in construction techniques and materials, and many will be subject to similar stresses as a result of climate change.

Some funding is likely to be available for ongoing maintenance and the repair for damaged bridges – but this is dependent on location, ownership and the legal status of the route which the bridge carries. Those which are situated on public rights of way and highways are more likely to be maintained and inspected regularly. This increased level of oversight will also apply to those bridges which are listed. Funding from public sources or grants is more likely to be more easily available to bridges on land owned by organisations and charities such as the National Trust than individual private owners.

Key adaptation recommendations for clapper and packhorse bridges

Improve current condition to increase resilience

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are aimed at improving the condition of the feature at present, therefore making it better able to withstand future changes to climate.

• Slow the flow of water into rivers by ensuring landscape scale natural flood management in the uplands through blanket bog restoration, diversification of heather moorland and significantly increased woodland and scrub regeneration.
• Stabilise watercourse banks by encouraging tree and scrub growth adjacent to the channels where appropriate to reduce sedimentation and slow run-off entering.
• Encourage the designation of more structures by increasing knowledge base of these features.
• Engage with landowners and offer advice and funding streams for maintenance and repair of bridges.
• Control invasive species such as Himalayan balsam which can lead to the destabilisation of watercourse banks.

Improve current condition to increase resilience: Targeted conservation efforts for important sites and at risk areas

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are conservation measures aimed at those sites that will have the biggest impact for this feature – either because they are particularly important for the feature or because they are most at risk from climate change.

• Conduct a survey to collect more detailed information about the current condition of these features and identify those individual structures which are most at risk.
• Select a sample of bridges which can be routinely monitored to track any deterioration in condition over time.