Ancillary, Contributing Area and Flow Surveys

Lot A Ancillary (Manhole and Pumping Station and other surveys as required)

Ancillary surveys consist of measuring specific asset parameters such as depth, diameter, pump rate etc. They are typically required when drainage system records are poor or missing. The information is used to update the hydraulic models which are then used for various projects - detailed solution design, investigations, root cause analysis and so on.

• Other surveys on occasion are requested. For example, a balancing tank survey or a storage channel survey. These surveys are included in the scope of a Manhole or Pumping Station Surveys, but not always requested or needed and are referenced in the specification)

Contributing Area Surveys are undertaken to understand how networks perform during periods of rainfall and to produce calibrated hydraulic models. They consist of visual observation of where the roof drainage is connected and where necessary undertaking a sound test to establish connectivity. When rainwater enters the foul sewer network it can cause excessive flows in pumping stations and treatment works. This may cause polluted sewage to overflow into streams or possibly within a residential property. The first step in reducing the storm flows within a catchment is to identify where storm water sewers are separate from foul, and those areas which are combined into the one system.

The data provided from the survey can enable decisions on making changes to the network with the outcome of reducing stress and possible incidents of sewage overflow /flooding.

Flow surveys are needed in order to record actual flow data at critical locations of the sewer system. They consist of installing sensors for measuring and recording the flow depth and velocity in sewers. The information is then used to calibrate and verify the hydraulic models so that the simulated performance matches the observed flows. The verified models support decision making about improvements to the network, efficiencies and cost saving