SuDS Assessment for a Commercial Home-Builder

GeoSmart was asked to produce a SuDSmart Plus Report to assess how the development of greenfield land into residential properties may impact the flood risk to off-site receptors as a result of the increase in surface water runoff generated.

The planned area of impermeable ground cover was also used to estimate runoff volume and calculate the required volume of water to be discharged on-site.

Since the site was underlain by permeable limestone, a soakaway was proposed as a feasible option for the attenuation and discharge of the excess runoff directly into the ground.

We were instructed by a commercial home-builder to produce a SuDS Assessment Report to calculate an estimate of the increase in surface water runoff generated following the proposed development of three residential properties at the site. The existing land-use comprised one dwelling with a proportion of undeveloped greenfield space.

The amount of impermeable ground cover in the existing and proposed development was used to estimate the increase in surface water runoff generated following an extreme rainfall event taking the effects of future climate change into account.

The hydrological and hydrogeological context of the development was reviewed to assess the potential for discharging the surface water runoff through a SuDS scheme.

The site was underlain by permeable limestone and a soakaway was proposed as a feasible option for the attenuation and discharge of the excess runoff directly into the ground. Assuming the scheme was implemented in line with our proposed plans, there was considered to be no off-site flood risk.

Recommendations were made in our report to conduct percolation testing at specific locations across the site where the conditions were likely to be most favourable for a soakaway scheme.

The client was referred to our sister company ESI Ltd for more detailed design of the soakaway, taking into the account the availability of space on site, the total excess runoff due to the development, and the permeability of the ground.

The outcome was a cost-effective solution where we worked with the client at every step to devise a SuDS scheme that was simple and very effective at reducing the impact of the proposed development on the future runoff volumes from the site.

Where further planning and design works were required, we referred to ESI who were well informed and coordinated to meet the needs of both the clients and the regulators.

The client was pleased with the result and benefited from our ability to seamlessly co-ordinate the required further work through ESI.

Client Benefit

GeoSmart undertook a SuDSmart Plus Report in 15 working days. Follow-on percolation testing was organised by us through our sister company ESI, who were well informed and coordinated to meet the needs of both the client and the regulator.

The client was pleased with the result and benefited from our ability to seamlessly co-ordinate the required further work through ESI.