Category Archives: Engineering Features

Converting stormwater into a sustainable water supply – March 2022

The Francisco Street Reservoir now serves as a source of useful non-potable water at a park for the local community, thanks to a stormwater collection system underneath.

Francisco Street reservoir was the first large reservoir in San Francisco, California when originally built in 1859. Decommissioned in the 1950s, the site was to be redeveloped but the Francisco Park Conservancy fought to keep it as a natural resource that would include harvesting rainwater. Underneath the 1.8 hectares Francisco Park is a stormwater capture and reuse system which was installed in 2021 to perpetually provide water for the park’s irrigation and toilets.

ADS StormTech chambers store water for reuse at this park in San Francisco.

How the stormwater system works

The stormwater is stored in a 1.9M litre cistern at the top of the hill before being transferred to the service building, where it flows through a series of filtration and disinfecting processes. This ensures that the water meets public health regulations, while saving 5.7M litres of potable water every year.

The engineers decided to use a system of arched chambers because they would provide the largest storage volume per square metre.

“The reservoir is on a slope that is just under 20%. It’s a very challenging site from a variety of perspectives,” explains Sherwood Design Engineers (San Francisco) principal Cody Anderson who is responsible for the stormwater system.

“Normally you’d have your catch basin at the bottom of the site. Here, the historic reservoir is midway up the slope, so half the runoff is collected via gravity flow and the rest collected at the bottom of the site and pumped. All captured runoff flows through the screening filtration and into the chambers for storage and later use.”

Equipment used

Three hundred and seventy two ADS StormTech chambers, were installed using a 35m by 45m area of the existing reservoir and then covered with soil. This gave a total storage capacity of 2,000m3 of water in a 1,682m2 footprint. ADS StormTech chambers provided the best ratio of storage volume to footprint area.

The StormTech chambers are independently tested, BBA-approved and fully compliant with ASTM F2787, F2418 and F2922 stormwater storage systems standards. StormTech is typically used for below ground SuDS attenuation projects and more than 2.5M chambers have been used successfully around the world in over 40,000 projects. Three StormTech Isolator Rows are included in the Francisco Street reservoir system. These patented water quality treatment devices are integral to the StormTech system. They capture the “first flush” and trap sediment and other pollutants coming from stormwater runoff.

StormTech chambers come in a wide range of sizes, making them easy to install for all conditions. They are highly adaptable and can be configured around obstacles as well as affording multiple inlet and outlet positions. Standard pipe manifolds, manhole and access chamber inlet/outlet structures and flow controls can be used.

Isolator Row is essentially a ‘free’ in-built water quality treatment device

Reclaiming an area of San Francisco

“There are competing products on the market,” says Anderson. “We needed to store as much water as possible in the given area. We work on projects around the globe with an emphasis on sustainable development and we’re known for having the vision and the technical capacity.

“The Francisco Park is one of those projects of a lifetime. It’s reclaiming an area in the city of San Francisco that is now a beautiful park for the people.”

StormTech helps manage Britain’s wetter weather – Nov 2021

As British weather officially gets wetter, ADS StormTech – the world’s preferred proprietary stormwater attenuation system – arrives in the UK.

Isolator Row is essentially a ‘free’ water quality treatment device

With Britain hosting the UN’s Climate Change Conference this November, the recent State of the Climate report was greeted with interest by politicians and construction professionals alike. Published by The Royal Meteorological Society, the report showed that Britain had become 6% wetter, on average, over the last 30 years (1991-2020). Additionally, six of the 10 wettest years since 1862 have occurred since 1998.

This wetter weather will challenge the UK’s drainage infrastructure and the management of water quantity and quality. Fortunately for engineers working on rainfall management and stormwater attenuation systems, StormTech – the world’s preferred subsurface water management system – is now available in the UK.

StormTech is manufactured by ADS, America’s largest manufacturer of corrugated thermoplastic drainage pipes and a specialist in water management systems. StormTech has a long and successful track record with over 40,000 installations – including St Petersburg and Guernsey airports – ranging from the DC United stadium to Lidl stores in the USA.

StormTech’s design flexibility manages construction around obstacles like lighting columns

StormTech provides a durable solution for commercial, residential, industrial and infrastructure installations. As part of an integrated SuDS system, StormTech helps provide valuable surface space for parking, playgrounds or other amenities, and has many benefits over alternatives such as geo- cellular crates, large diameter pipes and vaulted systems.

Flexibility is designed-in to StormTech. The chambers are injection moulded to ensure consistent quality and performance, and even the colour and semi-elliptical shape are deliberate engineering choices. The chambers shape the embedment stone into structural arches forming load bearing columns. This makes StormTech more adaptable than other systems, as it’s the stone that transmits the majority of the load.

StormTech chambers lock together, providing uninterrupted access for easy inspection and maintenance, and the wide range of sizes makes it easy to optimise systems for all conditions, including shallow invert depths and reduced footprints. They’re also highly adaptable and can be configured around obstacles and afford multiple inlet and outlet positions. Standard pipe manifolds, manholes, access chambers and flow controls can be used.

StormTech incorporates the unique, patented Isolator Row, a built-in water quality treatment device, removing silt, sediment and other surface water pollutants. Isolator Row has been independently tested by universities and respected industry bodies and proven to remove over 80% of Total Suspended Solids (TSS) and other water-borne pollutants including metals, hydrocarbons, phosphorus, and nitrogen. Isolator Row provides two treatment stages: settling (gravity separation) and filtration. Unlike other sub-surface systems, Isolator Row provides a “free” water quality treatment device as an integral part of the stormwater attenuation system.

StormTech’s Design Tool 2.0 provides quick and effective system design optimisation that integrates with CAD and other design, engineering and specification documents. Sample designs and layouts are available, as are a team of specialist design engineers. For installers, the SiteASSIST app includes comprehensive instructions and videos, making working with StormTech fast, easy and efficient.

StormTech affords low embodied carbon per m 3 of attenuated water compared with alternative systems and is fully recyclable. It is independently tested, BBA approved and compliant with ASTM F2787, F2418 and F2922.

Originally published in November 2021