Watering the Big Apple

Another 100 years of clean water

Reservoirs high up in the Catskill Mountains connect to New York City through a 148km aqueduct built more than 100 years ago. During its construction, current affairs magazine Harper’s Monthly in 1909 described the Catskill Aqueduct as one of the most notable engineering enterprises ever undertaken, second only to the Panama Canal. It remains a vital piece of infrastructure, helping to keep water flowing to taps for many of New York’s 8.6M residents.

Replacing the aqueduct would be hugely expensive. The entire Catskill Aqueduct system – including dams and shafts as well as the pipeline – cost approximately US$177M to build. With inflation that’s about US$2.5bn at 2020 prices. Remediating the existing aqueduct so water can continue to flow to New Yorkers for another 100 years is the most cost-effective and environmentally sustainable option.

We’re using digital tools – including building information modelling (BIM) and geographic information systems (GIS) – to help keep project costs down and minimise disruption to services by adopting a more progressive approach to delivery. “It’s where BIM meets GIS to reduce engineering costs and restore the aqueduct’s long-term operational reliability,” says project manager Cory Dippold.

Our project with the New York City Department of Environmental Protection (NYCDEP) focuses on the last 20km stretch of the aqueduct, known as the Lower Catskill Aqueduct. When complete in 2027, the work will ensure the aqueduct is retained in a state of good repair for the next century.

The many ups and downs

Gravity drives water flow along the aqueduct – from the reservoirs to the city – at a rate of 1.2m per second. But it’s not one continuous natural slope. There are many ups and downs along the alignment.

The highest point, the headworks at the Ashokan Reservoir screen chamber, is 152m above sea level. At its lowest, where the pipeline passes under the Hudson River, it is about 335m below the sea before rising again on the other side.

Topography along the alignment dictated construction. Most of the aqueduct – more than 88km – was built at ground level using a ‘cut-and-cover’ method to create horseshoe-shaped arches about 5m high and 5.3m wide.

Construction involved first excavating a trench, filling the bottom and sides with concrete, then pouring concrete over steel forms to construct the semi-circular roof, before the whole structure was covered with earth to create a berm in the land.

1.2m/s - rate of water flow along the aqueduct

Grade tunnels cutting through rocky areas, steel pipe siphons traversing local valleys, and pressure tunnels that plunge below creeks and rivers make up the remainder of the aqueduct. The pressure tunnels are deep below the ground to ensure they pass through rock solid enough to resist the water pressure, which is created by the force of gravity.

Along the aqueduct there are more than 30 culvert-drain sluice gates and almost 40 siphon-drain blow-off valves to control the water flow.

Tools of the trade

Engineers designing and working on the aqueduct in the first decade of the 20th century gathered geological information on the valleys, drilling hundreds of holes into the rock and taking samples (right) to determine its character and depth. Writing in the Journal of the American Works Association in 1918, chief engineer J Waldo Smith reported that engineers preparing for construction of the aqueduct and dams completed almost 50km of core boring and 22.5km of wash boring, conducted preliminary surveys over more than 5470km and completed numerous test shafts and trenches. ‘It was due to this carefulness, and this alone, that it was possible to conduct the whole work,’ he wrote.

Fast forward 100 years and today’s engineers have the advantage of digital tools to support their work. We’re employing the latest digital technology on the final 20km – the section connecting the Kensico Reservoir in Valhalla to the Hillview Reservoir in Yonkers – to evaluate its condition, design repairs and oversee reconstruction work as part of the NYCDEP repair and rehabilitation project.

Born digital

Cory explains that we adopted a ‘digital first’ mindset from the outset and refer to the project as ‘born digital’. In practice, that required making information management the backbone of the project. “It’s one of the most important ingredients to a successful job,” he says.

Cloud-based applications enable us to maximise collaboration between everyone involved, from engineers and designers to contractors and the client.

The project uses Microsoft’s web-based collaborative platform SharePoint, which has been configured to fully enable effective management of a digital job. Information and documents in the site cover, for example, commercial and risk management, scheduling, invoicing, standards and protocols, reporting, cost estimating, and health and safety.

We established a connected data environment (CDE) using ProjectWise in the cloud, and the CDE provides the design management platform to support the development and delivery of all technical work. It enables geographically distributed teams, including 11 subcontractors, to securely work on files from any location in the world. Our in-house solution provides document control and deliverables management, while ProjectWise Spatial enables project teams to search for files using project maps.

A model for the future

GIS and BIM are separately valuable tools for the delivery of a linear project like the repair and rehabilitation of the Lower Catskill Aqueduct. Integrating them, so we could surface data from the GIS database in the BIM model and vice versa, allowed us to take our digital delivery of this project to another level.

The first step was to populate a GIS platform with legacy and current information. Over the years, the exact location of some assets had been lost. This is where cloud-based GIS provided real value, with smartphones and tablets used to update existing datasets. “The original diagrams are very good, so we knew roughly where everything should be, but over the years something may have become hidden by vegetation or been altered, so GPS was used to find the exact location of every manhole, culvert, chamber, and blow-off valve,” says design manager Kristi Latimer.

Light detection and ranging (LiDar) is a mobile mapping technique and we used it to map the Lower Catskill Aqueduct corridor from the air. We then partnered with Esri, the supplier of geographic information system software, and Autodesk, which provides BIM software solutions, to combine GIS and BIM data in new ways.

All the information gathered on the aqueduct was brought together to build an accurate 3D model using Autodesk InfraWorks, software that enables designers and civil engineers to plan and design infrastructure projects in the context of the real world.

“We have created a digital reality model that reflects the project,” says Kristi. “It combines critical asset information using geometric, geo-spatial and parametric data to give project stakeholders more insight into the project and surrounding context than ever before.”

Carrying capacity

Built to transport 2.49bn litres of water a day, the capacity of the aqueduct now is about 12% less than in 1915.

All assets age and the Catskill Aqueduct is no different. Biofilm or surface deposits – a naturally occurring layer of micro-organisms – has built up on the inside walls of the aqueduct over the past century. It creates friction inside the aqueduct, slowing and reducing the water flow. Trapped air can also reduce flow and capacity.

2.23bn litres/day capacity now

2.38bn projected litres/day capacity after clean-up and repairs

After more than 100 years of service, the infrastructure also leaks in places. Water seeps out through cracks in the concrete walls or joints in the cut-and-cover tunnel segments, while some isolated leaks bubble to the surface from the pressure tunnels.

Cleaning the inside of the aqueduct, repairing leaks and defects and installing new chlorination facilities will help maintain the condition and flow of the aqueduct over coming decades, raising daily capacity by about 151M litres.

Going inside

To restore capacity, you need to first find out the condition of the inside of the aqueduct.

BIM provides good geometry and geo-positioning, but to effectively investigate conditions inside the tunnel we needed high resolution images. To get these, we used digital photogrammetry with ground-based mobile LiDar to provide a visual and geometrical image of the tunnel surface at a specific place and time, essentially replacing field investigations with a digital model. This approach provided a hybrid digital reality model to locate the exact position of surface leaks, spalls, cracks and other defects.

We tested and validated our approach and the technology in a 1.6km section of the tunnel that was no longer in use, completing a task that would normally take days in a few hours. The images and information were then processed, and each defect assigned real-world co-ordinates (geo-reference) with a unique ID, thus creating a digital model of the aqueduct with the issues clearly noted, and a geo-database of each fault.

We’re now taking our interior digital inspection of the tunnel a step further, exploring how artificial intelligence and machine learning can increase the quality and efficiency of the process. We’ve trained computers to identify, tabulate and quantify each defect. It’s a pilot, but early results are very positive with nearly all defects identified and classified correctly.

The end goal is to put significantly more computing power into the hands of our best engineers to help them deliver higher quality outputs by eliminating errors associated with repetitive tasks.

Fit for the future

The Catskill Aqueduct remains in constant use. Shutting it is costly, risky and immediately impacts the water supply of millions of people. Inside the tunnel is a permitted confined space, so less time spent inside examining the interior is better for the health and safety of engineers. It also reduces the risk of contamination from people and foreign objects entering the system.

Our digital approach is estimated to reduce the number days for field investigation from 63 to 19 and the number of shutdowns for inspection work by 80%. The overall quality of the digital observation also tends to be better than when people are working in difficult, nearly blackout site environments.

19 days for field investigations instead of 63

80% reduction in shutdowns for inspection

10/10 ‘excellent’ rating from client during annual project review

Beyond this, our digital approach to field data collection, information management and BIM resulted in the work being completed ahead of schedule, and under budget in the first two years of the project.

By integrating digital workflows in a geographic context we’re helping to reduce costs and to restore the 100-year-old engineering marvel to a state of good repair and long-term operational reliability – fit for another century.

Industry learning

In an engineering consultancy industry first, Cory spoke about how our team successfully integrated BIM and GIS data into one model before 20,000 people at the Esri 2018 users conference. He also showcased our work on the aqueduct at the 2018 Autodesk University event in Las Vegas – giving the architecture, engineering and construction keynote to a live audience of more than 10,000.