We are living at a time of existential crisis for wildlife, people and the environment, resulting from human-made (and absolute) climate breakdown. The impact of our behaviour on the environment has never been more obvious or more prominent as it is today. The legacy of our industrial past and its impacts on air, land and water in its entirety is contributing to climate change and is acting as a major physical barriers to progress towards a greener and more sustainable future for current and future generations.

The California Country Park and the Longmore Lake Dam are situated right in the heart of Royal Berkshire just outside Wokingham. Through a combination of Wokingham Borough Council’s ambitions and public interest, improvements to the Longmore Lake Dam, to increase the capacity of the water body to accommodate for climate change and reduce localised air pollution, is becoming a key focus.  The strategy will also account for flash flooding events, by implementing engineered flood mitigation solutions.

As the environment and climate are ever changing, the existing formal path network no longer provides the access or amenity required to maximise the potential of Site of Special Scientific Interest (SSSI) that surrounds the area.  To increase public awareness of the issues associated with climate change within the local area, this work also supports improved access to the Rare Bog connecting the public to local and rare nature resources.

California Country Park is home to a wide variety of flora and fauna befitting its designation by Natural England as a Local Nature Reserve. The 14 hectare site combines a unique make up of secondary woodland, heather and bogland known as the Longmoor Bog and is one of a few examples in Berkshire of a base-poor valley mire.

The area is used regularly by dog walkers, educational groups, volunteers and the general public, deepening the importance of these works and promoting the natural beauty and natural beauty, whilst ensuring the safety of the park users.


To provide essential flood storage, increase access and improve resiliency Sanctus were appointed to demonstrate their proven track record once again. As one of the country’s leading environmental contracting specialists, Sanctus were delighted to be asked to deliver and implement a series of environmental interventions to make this ambition a reality. In partnership with Wokingham Borough Council, 17-week contracting programme had three key phases:
The first phase is centred around the installation of bespoke new culvert and stilling basin in the footprint of two obsolete drainage pipes providing attenuation of additional discharge during a flooding event. Sanctus constructed a coffer dam. This temporary works was installed to allow open dry working and rapid construction methods for laying concrete, reducing program time, sedimentation and keeping our workers safe.

The second phase of works was the decommissioning and demolition and recycling of an existing spillway structure with the construction of a new higher capacity more resilient spillway providing an attenuation system to account from ever more extreme flooding conditions.

Sanctus understood that minimum disturbance should be made to the park users, and access should be granted throughout the entirety of our works. To enable this Sanctus installed an exclusive floating pontoon walkway which allowed for the parks valued loop walk to be continued, whilst diverting park users around our discrete working  areas. Sanctus ensured that the walkway was compliant for less accessible users, incorporating ramp structures, with extra width for the crossing.

With the work site sitting in an area classified as both SSSI and Local Nature Reserve, Sanctus ensured that all earthworks on site, from the engineered drainage improvements within the reservoir to the installation of footpaths were sensitively designed to reduce material handling and machine movement to minimise the disturbance to the surrounding environment. Using biodegradable fuel and products.

The Programme

Installation of a Floating Walkway

The 65 metre long floating pontoon footpath was fundamental in stakeholder engagement and buy-in to our works.  Allowing users of all abilities to continue to use the parks and view our on going works throughout the program.

The new walkway provides improved access through the middle of the surrounding reservoir and provides a fantastic opportunity for the general public and regular site users to engage with the scheme.  By employing a floating walkway, this diverts the public away from the work place entirely and is not only an innovative / playful addition to the park but the safest solution whilst constructing the spillways and footpaths. Other access works involved the installation of a 190m walkway from the existing track into main spillway and the crest towards the SSSI. Providing a lasting opportunity to engage with the SSSI and observe it’s environmental benefits.

Sheet Piled Coffer Dam System – installation of a new culvert and stilling basin

Sanctus are committed to working sensitively, safely and sustainably. The prior condition of the original drainage system consisted of 2 degraded drainage pipes that outflowed into a nearby siltation and settlement pond. Sanctus replaced the original piped system with robust concrete box culverts. Providing greater command of the spating flows from spillway from the control weir, through the stilling slab before discharging into the existing surge/silt pond and into the bog area beyond. The engineered stilling slab was installed to ensure that the energy of the water surging through the culvert dissipates the energy, preventing erosion and reducing future maintenance, even in extreme weather events.

To ensure the Box culvert sections could be installed quickly, safely and efficiently a sheet piled cofferdam consisting of four corner piles were installed to depth to provide achoring support and initial shoring whilst 60no. piles were driven in at depth to secure the area to allow dewatering and dry working conditions.

Demolition of existing and construction of new main spillway

Sanctus programmed to construct and deliver the new main spillway prior to the demolition of the existing defunct structure. This minimised the disruption to park users by eliminating footpath closures. Once the new spillway was delivered and opened for access and water flows, Sanctus were able to begin the sequenced removal and subsequent decommissioning of the existing spillway. This also minimised the risk from inundation and siltation from storm events.

The Challenges

Working within the boundary of a SSSI

This environment is home to a diverse range of flora and fauna including species of grey willow (Salix Cinerea), downy birch (Betula pubescens) and an area of wet heathland and fauna including a variety of breeding birds including woodcock (Scolopax rusticola), great spotted and green woodpeckers (Picus viridis), treecreeper (Certhia familiaris) and tree pipit (Anthus trivialis)., Sanctus ensured that an environmental watching brief to ensure Sanctus had minimal impact on the SSSI. All earthworks that took place were designed to reduce material handling and machine movements in order to keep disruption to wildlife and disturbance to the water column or silts to a minimum. Biodegradable fuel, additives and hydraulic oil was used for the plant to reduce the risk of pollution to the controlled waters in the event of a spill.

Working in adverse weather conditions

Sanctus undertook active water management to maintain safe working levels in works areas to ensure delivery within the program. This was managed using Sanctus’s bespoke water treatment and pumping system, deployed under the groups competency management system to safely discharge into the reservoir. A site flood manager was appointed with automated telemetry systems to allow real time adaptions to changing site conditions.

These proactive measures removed the risk to Sanctus personnel as well as this unique and special site.


During the COVID-19 pandemic, there has never been a more important time for the public to access the natural environment, especially in urban environments where social and economic inequality is greatest and physical and mental health are frequently challenged. Sanctus are delighted to have helped restore the connection between the SSSI and the public through the installation of the footpath diversion whilst also improving the flood management within the Longmore reservoir. This has not only allowed for better drainage and the available capacity of water held within the reservoir but has also improved the aesthetics of the site. Given that this is a popular area for the public, maximising its restorative potential is the right thing to do for people and wildlife. Sanctus are confident that wildlife and visitors alike will benefit from the betterment of the site, whilst highlighting our ability to work in challenging environments.