Our drainage specialists have substantial experience of developing effective drainage solutions which are unique to each site. Whether it is an extension in London which requires surface water management, or a garden village where sustainable drainage (SuDS) forms part of the wider landscape strategy, our team understands the importance of well-engineered designs.
Whilst the focus tends to be on surface water management, wastewater management and Section 98 agreements can just be as important. Our experts are well versed in assisting on these matters and are happy to advise you on requirements.
Drainage Strategies
Drainage Strategies are required to manage water generated by developments. Our team of qualified drainage engineers have extensive experience in providing advice on how management of surface and foul water can be achieved. Following both national and local policy, we will work with the design team to ensure that industry best practice is followed, and the drainage strategy provides socio-economic benefits to your proposed scheme. Some sites can prove to be challenging, either due to steep land levels or limited methods for discharging water. Where this is the case, we will engage early on with relevant stakeholders to overcome any potential constraints and provide a suitable solution which works both for your project, whilst also satisfying local requirements.
Surface Water Management
New development has the potential to increase the risk of flooding to neighbouring sites and properties through increased surface water runoff. Our drainage engineers can assess both the existing and proposed site drainage to accurately quantify the runoff rates, flow pathways and the potential for infiltration at the site.
This assessment considers the practicality of incorporating Sustainable Drainage Systems (SuDS) into the scheme design, with the aim of reducing the risk of flooding by actively managing surface water runoff. We will work with the wider design team to ensure that any SuDS form an integral part of the wider landscape design and provide multi-functional benefits to the public.
Foul Water Management
Where new development is introduced, it may be necessary to demonstrate that there are means of disposing wastewater sustainably. Depending on the location of your site, this could either be via a connection to a public sewer subject to available capacity, or package treatment plants where no sewers are existent. Regardless of the location, we can assist in determining the best solution for your development and enter dialogue with necessary stakeholders to confirm acceptance.
Hydraulic Modelling
For developments such as minor and non-major, simple volume storage calculations for SuDS may be sufficient to demonstrate that surface water runoff can be managed sustainably. However, for most drainage strategies, a hydraulic model is required to estimate pre- and post-development discharge rates.
Herrington Consulting has a range of numerical models that assist in the development of Surface Water Management Strategies. These include FEH, ReFH and Causeway Flow+.
Where drainage flow paths have to be modelled, our in-house numerical flood modelling capabilities can assist in determining the impact of the development, taking account of existing features such as the drainage network.
Detailed Drainage Design
Once the concept of a drainage design has been approved by the Local Authorities as part of a planning application, a detailed drainage design will be required. The design typically requires liaison with manufacturers to take account for product-specific requirement. We can advise on appropriate products and prepare associated drawings which can be used for construction.
Section 98 and Section 106 Applications
For some development, a new connection to the public sewer may be required. A Section 98 requisition is required where a new public sewer is necessary, whereas a Section 106 agreement relates to a new connection to an existing public sewer. In both cases, we can assist with the formal request made to the sewerage undertaker.
Verification Reports
To ensure that the drainage design has been implemented and constructed as approved by the Local Authorities, a verification report may be conditioned. As part of the works, our specialists will collate evidence throughout the construction phase and present the information to the authorities in form of a report, with the aim of discharging any related condition.
Nutrient Neutrality Assessment
Where development is shown to result in a potential increase of nitrogen and phosphorus entering designated protected areas as defined by Natural England (NE), a Nutrient Neutrality Assessment will be required to demonstrate that any impact can be mitigated. We apply NE’s calculator and set out a mitigation strategy where possible.
Water Efficiency
With water scarcity becoming more prevalent in the future due to climate change, some Local Authorities may request evidence that proposed development can achieve water neutrality or a specific water consumption rate. We can assist in the preparation of required statements which set out efficiency measures and related calculations.