Suds drainage

Sustainable Urban Drainage Systems : Improving Water Quality

 

John McPeake, Technical Sales Manager at Wavin Ireland discusses the benefits of improving water quality using Sustainable Drainage Systems (SuDS) and the barriers which need to be overcome to increase their usage.

 

The Environmental Protection Agency is clear that there are deficiencies in many public sewers and waste water treatment plants, due to a legacy of under-investment. This has led to wastewater from some areas discharging into the environment without adequate treatment. In 2020, treatment at 12 of Ireland’s 174 large urban areas failed to meet European Union standards set to protect the environment. Over half (54%) of all the wastewater collected in Ireland’s public sewers is collected in the 12 areas that failed the standards.

 

 

Reducing water volume and pressure on sewage networks

 

In urban areas, surfaces tend to be covered by buildings, roads and paths this reduces natural infiltration for rainfall events. Many of the old public sewer networks are combined systems – drains for both foul wastewater and stormwater. During major rainfall events these ageing, and often over loaded networks incorporate storm overflows that bypass the treatment plant with direct discharge to rivers, lakes or sea outfalls causing pollution and public health issues with bathing waters. Managing stormwater at the source is a basic principal of a Sustainable Drainage System (SuDS) and it reduces the volume of water that is discharged into a sewage network. Sustainable drainage systems (SuDS) can play an important role in improving water quality and could be at least part of the answer to Irelands growing issue of wastewater and pollution.

 

Infiltration

 

Allowing stormwater water to naturally permeate into the ground, not only reduces the volume of water that runs off into the drainage system but also replenishes the groundwater. Soakaways are the most common form of infiltration, but infiltration trenches, infiltration basins and rain gardens are also key infiltration components. Geo-cellular units such as Aquacells with 95% voids ratio, are an efficient method of providing both the surface area and storage volume that are pre-requisites for a soakaway design.

 

Slowing the flow and flood resilience

 

There are many different SuDs components that can slow the flow of storm water and attenuate or temporarily store it, allowing it to be released in a slower and more controlled manner. Geo-cellular tanks with 95% voids ratio are particularly effective at providing storage capacity for a sustainable drainage system. Engineered solutions such as vortex flow control valves enable precise control of discharge flow rates from attenuation systems.

 

The barriers to sustainable drainage systems

 

Despite the benefits provided by sustainable drainage systems in terms of climate resilience, flood prevention, water quality, biodiversity and better places to live and work, the use of sustainable drainage systems in Ireland is driven by Local Authority planning requirements for new developments. SuDS is  mandatory for all new developments, except where the developer can demonstrate that its inclusion is impractical due to site circumstances. Where SuDS cannot be provided, the developer must provide alternative means of dealing with pollutants.

The ‘Greater Dublin Strategic Drainage Study  (GDSDS) issued in 2005 is still the reference document for Civil Engineers. The GDSDS states that co-operation between stakeholders in promoting SuDS, including developers, designers, the Department of the Environment, Council Drainage, Planning, Parks and Roads Departments and the general public, is required.

In Ireland, we have the technical expertise but need the leadership to bring all the stakeholders together to highlight the benefits of SuDS not only for flood mitigation but also the environmental and social benefits.  The reasons the acceptance of SuDS has been slow in Ireland include; differing local planning requirements,  limited budgets and resources for maintenance and lack of incentives for developers to incorporate SuDS in their schemes.

There needs to be a whole of life solution with one organisation leading the SuDS agenda.