Prior Investigation v Watching Brief

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Prior Investigation vs Watching Brief; what’s the right solution?

Lindsey Weaver, Principal Heritage Consultant at Cogeo

Everything we do for a project involves balancing risk. Heritage is no different. An archaeological dig doesn’t depend on planning permission being granted, meaning every developer has a choice; risk carrying out exploratory works for a site that may not gain consent, or risk waiting to see what is unearthed and delay construction.

Where a development site may have buried archaeology, two approaches are generally accepted:

- Pro-active: Prior Investigation
- Reactive: Watching Brief

Prior Investigation

Provides certainty

Control over timescales

Doesn’t require planning permission

Carried out at risk

Watching Brief

Required after permission granted so no financial risk

Aligns with confirmed construction timelines and phases

Delays to construction outwith developer control

Prior investigation allows archaeologists to survey a percentage of the development site before planning permission is granted, with any necessary mitigation incorporated at the design stage. While this process carries some risk – since permission for the overall project is not guaranteed – it helps reduce potential construction delays by addressing any required archaeological mitigation early.

A watching brief involves live monitoring of groundworks once Planning Permission has been granted by way of a Condition on the Consent, with all works required to stop if archaeologically significant material is unearthed. This risk can delay the construction timeline but is only necessary after consent is granted.

The Process

Both processes require the submission and approval of a Written Scheme of Investigation, a framework that sets the scope of works to understand archaeological implications within a development site.

Project Timeline

*If required, with all works on site stopping until satisfactory mitigation agreed by all parties.

Archaeology in Action: Solar Farms

Evolution of thought

With the knowledge gained from solar projects since the 2010s, local and national archaeological bodies have raised significant concerns that piling may disturb and damage undiscovered archaeological remains.

These concerns have led to an evolution of approach from a reactive watching brief to proactive prior investigatory works. This provides better archaeological knowledge whilst the project is in development and allows mitigation to be integral to design.

Cogeo's advice

Being proactive in your approach can always be of benefit to a planning application but inevitably comes with risk. If Heritage, particularly buried archaeology, is considered a project or design risk, Prior Investigation would likely be a positive and proactive solution.

However, Heritage needs to be contextualised within the overall planning framework and is only ever a part of the determination process. If other factors could lead to the refusal of an application, waiting to carry out a watching brief may be the more pragmatic approach. This must be balanced against impacts on construction timescales.

The best advice we can give is to ensure you understand your options and your risks. Every site has different constraints, and sensitivity will depend on both the development and design. The most proactive approach you can take is to engage early in the process before making design decisions, empowering you to balance the risk vs reward of archaeological investigation.

Key fact

A generally accepted method for archaeological evaluation in England is to assess a 3% sample of the development area in addition to a geophysical survey. In Scotland, an 8% sample size is typical due to the unreliability of geophysical survey results caused by the high volume of iron pyrite in the soil.