• The Lake is 2m deep. The bottom 1.54m are used for irrigation, the next 0.16m is for the attenuation of rainwater, with the remaining 0.3m for freeboard.
  • Total Storage Capacity = 9,164m3
  • Irrigation Storage Capacity = 7,098m3
  • Attenuation Storage Capacity = 897m3
    
    
• Based on the RHS Wisley rainfall data and the catchment size, Clear Lake should capture and reuse 6,600m³ of rainfall in an average year.
  
  
• The earthworks for the Lake were designed using Civil 3D and ensured no import or export of material was required. This approach helped minimise the project’s impact on the environment, whilst also keeping the costs down.
  
  
• When the Lake is full, it overflows into an infiltration basin at 1l/s, and if the infiltration basin is ever full, excess water will overflow into the local ditch network.
  
  
• The water is pumped from Clear Lake to the existing Battleston Hill tank, where it is distributed through the gardens.
  
  
• There are 5no aerators in the Lake to help create aerobic conditions to naturally break down nutrients.

All Stakeholders agree that the Lake achieves the objectives of the brief, and it is collecting large volumes of rainwater, which demonstrates the amenity value and the environmental benefits including rainwater reuse, biodiversity habitat creation, rainwater treatment and attenuation will be met. 

The scheme was completed on budget, on time and to the satisfaction of the project team and hopefully the future visitors of the RHS Gardens at Wisley!