RHS Garden Bridgewater


The RHS are creating a new 62-hectare garden on the former Worsley New Hall site in Salford. The new garden project will be the largest in Europe and planning approval was given in June 2017.

We were invited in October 2017 to join the existing multi-disciplinary team to provide the specialist hydrology, hydrogeology and hydraulic modelling services required to take the concept designs to tender stage. The challenges were threefold:

1. To advise the RHS on where and how to achieve sustainably the water requirements for the proposed existing and new lakes and for the site irrigation requirements in a sustainable manner.

2. To provide a hydraulic design of the conceptualised new ornamental lake, stream and linkage to the existing lake using available water from the surface water drainage system to provide a continuous stream flow.

3. To undertake a structural survey of the existing lake and advise on remediation measures to ensure that the lake both retains its designed water level and meets the RHS’s operation requirements.


Our hydrogeology team, led by Mike McDonald, initially undertook an assessment of potential groundwater resources. A water balance assessment for the existing and new lake was conducted and we developed a strategy for water usage across the site.

Using the concept design proposal for the new lake and stream, a HEC-RAS model is being developed to demonstrate the hydraulic performance of the system and to advise on water requirements to maintain flows and levels to meet the Landscape Architect’s aspirations. This includes natural run-off and supplementary recirculating of water through the system.

Our initial solution was to employ specialist underwater diving engineers to undertake the existing lake survey as the RHS were keen to retain as much of the lake water as possible. The existing lake is however heavily silted and we have agreed with the RHS that the lake will now be emptied prior to survey works taking place.


Sustainable water use is core to the RHS values. The benefit of the water assessments undertaken and the development of a water management strategy will enable RHS Garden Bridgewater to be developed primarily using natural water resources within the site.

Using our hydraulic modelling expertise, we have also been able to advise on the utilisation of the attenuated drainage system for supplementing the new streamflow and lake recharge by proposing a pumped system.

Want to know more?

For more information on this project contact Chris Scott or Mike McDonald. You can also find out more on our flood and water management web pages.

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