Sustainable Drainage (SuDS) & Soakaways
Sustainable Urban Drainage Systems (SuDS) are drainage solutions that provide an alternative to the outfalling surface water either directly to public sewers or nearby watercourses.
A SuDS system reduces the flow of water from a single dwelling or housing group to what it would be if it was a greenfield site. This can be achieved by attenuating the water in oversized pipes, tanks or modular storage systems. It can also be achieved by the use of soakaways, balancing ponds and swales.
Planning regulations and Building Control require that surface water should outfall firstly to a soakaway, then if the ground is not suitable, to a watercourse and as a last resort to a public sewer. If it is to a watercourse or public sewer, then the surface water has to be attenuated to reduce the rate of discharge. The rate of discharge can be controlled by a reduction in the size of the outfall pipe, an orifice plate or more commonly a Hydro-Brake, which is a vortex flow control unit.
Soakaway tests can be done in two ways, either in accordance with Building Regulations or BRE Digest 365. The building regulations test requires two test holes to be excavated typically to a depth of 2.2m to 3.0m with a small hole excavated at the base of the test hole, which is filled with water and the time recorded for the water to drain away. Building Regulations state that this test method is not suitable for soakaways draining an impermeable area of more than 100m2.
The BRE Digest test is the one commonly requested by Local Authorities. This test generally involves excavating one test hole also typically to a depth of 2.2m to 3.0m, but the hole is filled almost to the top with water, and the time recorded for the water to drain away.
Test instructions and record sheets can be provided to clients to enable themselves or a contractor to carry out the tests. On receipt of the test results Sumner Consultancy can analyse the results and provide a design and specification for the soak-away.