Managing Stormwater on a Historic Irish Site

Aug. 20, 2014

Grangegorman is a suburb of Dublin, Ireland, situated on the north side of the city, approximately a mile from the city center. It has a long history of serving the people of Dublin, particularly with the establishment of the Houses of Industry for the poor in the 1770s and St. Brendan’s Hospital, built in 1810 to house mentally ill patients.

Until recently, much of the rest of the space had remained undeveloped and was considered brownfield, with the exception of a small portion that had been used as recreational playing fields. The land contains many mature trees and an array of buildings that are protected under the current Dublin City Development Plan, all of which date from the 19th century or before.

In addition, a high boundary wall surrounds most of the site, restricting access. The Grangegorman site has a diverse architectural, historical, and land-use character; however, the area is fragmented and cut off from surrounding residential neighborhoods. These factors had previously served to limit expansion and to discourage the coherent development of the area.

In 2006, the Irish government established the Grangegorman Development Agency (GDA) under the Grangegorman Development Agency Act of 2005 to revitalize the approximately 73-acre grounds. The GDA aims to create a vibrant new city quarter with a diverse mix of uses, in a way that is sensitive to the context of the Grangegorman area, its surrounding neighborhoods, and the existing community. The new complex will feature health, education, and community at its heart and will open up a previously walled-off part of the city. Ultimately, the redeveloped site will include:

  • a high-quality area with physical linkages to Smithfield, Phibsborough, Prussia Street, and the City Centre;
  • new health care facilities for the Health Services Executive, including separate centers for mental health, primary care, and elderly care;
  • a new urban campus for the Dublin Institute of Technology, bringing together all students and staff in one location;
  • new arts, cultural, recreational, and public spaces to serve the community and the city;
  • a primary school, public library, and children’s play spaces; and
  • complementary mixed-use development.

Cloudburst, headquartered in Navan, Ireland, is a sustainable water management systems company that designs, installs, and supports stormwater, floodwater, and rainwater technologies. The company was called in to specify sustainable drainage solutions to meet the expected needs of the project. Along with the main contractor, Ballysheed; Ireland-based Roadbridge Construction; and two Dublin-based design engineers, ARUPS and O’Connor Sutton Cronin, Cloudburst effectively delivered one of the largest infiltration systems to be built in Dublin to date.

Installing the open-bottom chambers

The development in Grangegorman is an extensive inner-city rejuvenation project and requires the creation of multiple concrete surfaces, which will prevent large amounts of water from filtering into the ground. Traditionally, a portion of this runoff was captured by a network of large pipe systems and later disposed of, without any treatment, into a nearby river.

“In accordance with best practices developed due to climate changes and the implementation of the EU Water Framework Directive [the governing body responsible for setting water-protection objectives], it is now mandatory to manage stormwater disposal in a more environmentally friendly way,” explains David Newman, Cloudburst’s technical director. “Because large impervious surfaces commonly lead to multiple impacts on stream systems, including higher peak streamflows, reduction of infiltration (which lessens groundwater recharge), and increases in pollutant loads to local water bodies, Cloudburst advised on the positive environmental impact of stormwater chambers in addition to the engineering design of the system.”

Historically, stormwater has been considered a quantity problem and has been dealt with by discharging it directly to other bodies of water or treating a portion of it in wastewater treatment plants. Sustainable Urban Drainage Solutions (SUDS)–such as those offered by Cloudburst–are decentralized solutions that take into account both the protection of natural resources and future compliance with the most recent legislative requirements. SUDS’ aim is to change the principle that water should be rapidly transported away from towns and cities. Instead, the products mimic the natural hydrological processes associated with water flows, which have been lost due to high rates of urbanization and impermeable surfaces.

One particular challenge the design team faced was tying the new subsurface stormwater system into the existing drainage invert levels. The design team chose a Cultec subsurface stormwater management system for a combination of stormwater retention and detention. The chambers have higher removal rates of phosphorous, nitrogen, lead, zinc, suspended solids, and organic carbon when compared to wetlands, water quality ponds, filtering systems, and swales. In addition, contractors from Roadbridge Construction ultimately chose to go with Cultec because they were highly impressed with the company’s customer service and product choices compared to other options.

The chosen system disposes of all stormwater onsite through infiltration and allows the runoff to help replenish the natural water table as would have happened naturally, before the site was developed.

Given the requirements of the site, including the 84,755 cubic feet (2,400 cubic meters) of must-have storage, the Cloudburst team chose to use Cultec’s Recharger 330XLHD model. With a capacity of more than 400 gallons (1,514 liters), this Cultec chamber is one of the largest available. Providing a balance of maximizing storage while using a small footprint, it best satisfied the requirements of the Grangegorman site. The unit is 52 inches (1,321 millimeters) wide by 30.5 inches (775 millimeters) high and has an installed length of 7.5 feet (2.29 meters), with a bare chamber capacity of 7.5 ft³/ft (0.7 m³/m). Because of its size, the chamber can help save land space and offer design flexibility. In all, the subsurface system provides 84,917 cubic feet (2,405 cubic meters) of storage.

Members of Roadbridge Construction, assisted by Cloudburst and Cultec, installed the subsurface system, which included a total of 598 Recharger 330XLHD chambers arranged in 26 rows beneath a set of grass tennis courts. Cultec’s No. 410 Filter Fabric encases the entire bed to prevent soil intrusion into the chamber bed.

“Roadbridge worked side by side with Cloudburst and O’Connor Sutton Cronin to design an attenuation solution for Grangegorman that had the minimum environmental impact during installation but also delivered the most positive environmental attenuation process,” says Ronan Kenny, commercial manager with Roadbridge Construction. “This solution was designed in accordance with best practice and in alignment with the EU Water Framework Directive. SUDS specialists Cloudburst recommended the Cultec Contactor and Recharger stormwater chambers, which proved to be the highest-quality system and also highly cost effective. Installation was fast and efficient, and we are delighted with the finished system, which is one of the largest ever completed in this country.”

The chambers are dome-shaped with perforated sidewalls and fully open bottoms to allow maximum infiltration. In addition, 25 HVLV FC-24 feed connectors were inserted into the side portals of the stormwater chambers to create an internal manifold system. The feed connectors have a larger flow capacity than a 12-inch- (300-millimeter) diameter pipe. The internal manifold feature available on the Cultec stormwater chamber allows for a more cost-effective and condensed bed size, because a costly and time-consuming custom pipe and fitting external manifold fabrication is not required. Installation is quick and efficient. Coupled with the plastic stormwater chambers, the manifold creates an underground detention field that will hold water until it can be cast out.

“A key benefit of using the Cultec chambers is that, over time, a natural biomass will form on the walls and floor and the geotextile membrane, which filters and helps to break down micropollutants and other contaminants that may be in the stormwater,” says Newman. “The chambers carry substantial point ratings under the LEED and BREEAM programs, making them of considerable benefit to clients and society as a whole.”

The stormwater management system was designed and installed in accordance with the Greater Dublin Urban Drainage Directive, Department of Environment Regulation, European Community Directives, Building Regulation, and Health and Safety Regulation.

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