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Photograph - The site of the development

SUDS Design, Monmouthshire

Low rate of permeability

Morton-Roberts were engaged to produced a design to dispose of the surface water from this small 'green field' residential development, comprising five properties, which was on the edge of a village in Monmouthshire.


Prior to our involvement, percolation tests had been carried out at the site which suggested that the underlying soil had a very low rate of permeability. This might have meant that SUDS infiltration techniques such as soakaways could not be used for the disposal of surface water. This would have been problematical since the site was some distance from any other means of draining the surface water such as a watercourse, surface water or combined sewer.

Our Client had an option to buy the site but without a realistic means to drain the surface water, the development would not have been viable and so our Client's investment to date would have been lost.

Further percolation tests

Following the initial percolation tests, Morton-Roberts were able to advise on the location and depth of further percolation tests to make the most of soil conditions at the site. This was particularly difficult because the locations available for any soakaways were limited due to the proposed very dense housing layout.

Permeable Pavements and 'geocellular block' soakaway

Based on the results of the further percolation tests, Morton-Roberts produced a design utilising SUDS techniques which included pervious pavement for the drives and a geocellular tank (ie 'crates') of large plan area to serve the building roofs. The design work was carried out utilising Micro Drainage Source Control software.

Drawings including layout plans and details of ancillaries such as the soakaway and pervious pavements were produced to satisfy the requirements of the Council's planners and building control.


This small residential development site in Monmouthshire would not have been viable without a realistic means to drain the surface water. Morton-Roberts were engaged to investigate the problem and ultimately designed the means to dispose of the surface water using SUDS techniques in the form of pervious pavements and a large plan area shallow soakaway.

Further details of our services are given within the following pages:

Drainage for new developments

Drainage Stategy Reports

Sustainable drainage systems (SUDS)

Alternatively please contact us for further details.

Photograph: The site, located on the edge of a village in Monmouthshire.