Using sustainable urban drainage systems for water and flood risk management

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The delivery of HS2 across England is likely to have a long-lasting impact on the built environment sector. Continuing our series reviewing how it is adopting and influencing best practice, we look at how sustainable urban drainage systems will support its water and flood risk management controls:

As winter closes in, water and flood risk management will become increasingly important on construction sites. But these measures are vital year-round, covering much more than just weather-related water management.

Proper management measures prevent sediment disturbed by construction works or bad weather getting into nearby waterways. They are essential for environmental protection as build-up of soil, silt, sand, mud or clay can seriously negatively impact watercourses and biodiversity.

They also prevent spills or leaks of fluids such as oil or fuel required to power plant, or paint or sprays needed for works, as well as protect workers and works from contaminated fluids already present on sites before a project begins.

Preventative and protective measures can be delivered using sustainable urban drainage systems.

What are sustainable urban drainage systems?

Sustainable urban drainage systems (SUDS) are controls to manage water and flood risk on developments. They include measures for silt control and erosion control such as silt fences, silt curtains and sediment mats. These manage water by capturing, diverting, filtering and/or absorbing water runoff to prevent silt from reaching watercourses.

When used efficiently and effectively they reduce flood risks, improve water quality on and around a site, and deliver environmental protection by protecting watercourses, habitats and biodiversity.

Delivering effective water management is more than just best practice – it is legally required by a number of regulations.

The Flood and Water Management Act 2010, Flood Risk Regulations and general Building Regulations set out legislation for England. And In Scotland, the Flood Risk Management Act 2009 and the Water Environment (Controlled Activities) (Scotland) Regulations 2011 outline the legal requirements.

Comprehensive guidance on how to adhere to legislation has been published by CIRIA (the Construction Industry Research and Information Association).

For HS2, its Environmental Minimal Requirements (EMRs), set out in Code of Construction Practice documents for each stage of the project, give guidance on how its teams will ensure water and flood risk management. These cover how to responsibly manage surface water and protect groundwater and how to manage and reduce flood risk.

Standardised management methods

HS2’s measures for surface and groundwater management are straight-forward and should be followed on all developments requiring groundworks. They begin with:

  • Identifying areas at risk of flooding and sources of potential pollution and works which could disturb or dislodge sediment or materials.
  • Producing maps of at-risk areas and plans for drainage across site, including what prevention and protection measures will be undertaken and how and when these will be implemented and monitored.

 

In practice, this sees developers implement silt control measures such as silt fences surrounding watercourses, to block or divert water runoff, silt curtains to control or block sediment or materials which reach waterways, or sediment mats to capture sediment from water.

Construction sites along HS2’s 340-mile-long development must have suitable site drainage systems, including ditches or drains with cut-off valves to manage and collect water. These must be coupled with plans and permissions for the discharge of dewatering, surface water run-off and/or waste-water created on the site, whether to soakaway or filtration systems, watercourses, foul sewers or using off-site disposal.

Effectively implementing, monitoring and managing measures such as these contributes significantly to reducing flood risk on a site. Additionally, other measures specifically for flood risk management include:

  • Consulting the relevant regulatory bodies and/or risk management authorities to identify any areas at risk of flooding, making use of the Environment Agency’s Floodline Warning Direct service for works which fall in at-risk areas.
  • Submitting a comprehensive flood risk report, where necessary, to the relevant authority (usually every three months), covering: the status of works, the identified risks and mitigation measures, any applications made for flood defense consent and any specific requirements or conditions of the approval.
  • Ensuring watercourses are clear of obstructions or debris to reduce the risk of blockages.
  • Taking immediate action if pollution risks are deemed unacceptably high, such as due to spills or leaks.

 

These control measures and standards for water and flood risk management can be observed and adopted on projects right across the built environment sector, no matter the size of organisation or type of operations.

Specialist management methods

HS2’s guidance also includes measures for working in areas where there is potentially contaminated land. This includes methods for dealing with intercepted groundwater containing high concentrations of contaminants, to limit the spread and prevent the potential negative impact of these. And since the project requires the use of heavy plant and machinery, HS2’s EMRs also reference the Control of Pollution (Oil Storage) (England) Regulations 2001.

Similar practices can, and should, be adopted on any other site type if applicable, including:

  • Ensuring spillage kits are stored at key locations during development, in particular at refuelling areas or with mobile bowsers, and that staff are trained in their usage. This ensures oil-based materials, such as petrol, diesel, waste, and vegetable or plant oil, along with above ground fuel and oil storage tanks, are correctly managed to ensure environmental protection.

 

All of HS2’s water and flood risk management measures will be implemented in line with the guidance set out in both GPP1: A General Guide to Preventing Pollution, GPP5: Works and maintenance in or near water, and in CIRIA’s C532: Control of water pollution from construction sites.

HS2’s delivery is bringing the built environment sector’s responsibility to the environment into sharp focus, demonstrating how infrastructure and construction projects must be delivered legally, safely and sustainably.

Following the above guidelines and working with experienced, expert contractors and suppliers will support adherence to regulations.

Get in touch for help and guidance on geotechnical and environmental measures and methods.