Foul and Surface Water Below Ground Drainage

Strategies and Analysis

Foul water is any wastewater emanating from WCs, urinals, sinks, showers, baths, washing machines, dishwashers, etc.  Surface water is rainwater falling on roofs, car parks, hard and permeable areas. In both cases, there is a need to manage the discharge in a safe and environmentally sustainable way.

Crofton offer an independent or integrated structural and MEP design service for buried foul and surface water drainage installations.  These could be serving a single property or an estate.

Foul water drainage needs to be tailored to each site, taking into account the local foul drainage network, its depth and capacity. We undertake a detailed design of underground drainage using MicroDrainage software for both simple and more complex network analysis.

Using MicroDrainage, we establish peak flow discharges based upon the fittings and activities within the development.

Normal practice favours natural gravity drainage, but where this is not possible due to the relative levels of the local drainage network, we can design a lift pumping station to overcome the problem.

Utilising our Revit based modelling, we work in 3D to ensure coordination with sub structures and other buried services and features, as well as taking account of the topography of the site and its changing ground levels etc.

We provide all drainage details for construction including pipe inverts, inspection chamber cover levels, setting out, and we detail all manholes and chambers with specifications for construction.

We will make applications for diversions and new connections (Sections 185 and 106) and liaise with the water authority to obtain consent.

We find an increasing incidence of there being a requirement to limit the discharge to the public sewers, particularly in urban environments. Where this problem arises, we can design suitable attenuation tanks and flow controls to achieve compliance.

Similarly, Surface Water drainage systems will usually be presented with increased flows due, for example, to increasing hard standing for car parking, or by the introduction of new buildings and associated run off from roofs.

It is now common practice that there will be a need to design to mitigate this additional load, by means of attenuation tanks, and flow controls, or by the introduction of semi-permeable surfaces to allow the rainwater to drain naturally into the ground.