Stories from DEP is a collection of feature articles
published in DEP's internal newsletter, Weekly Pipeline.
This article was originally published February 28, 2012.
City Siphoned All its Engineering Talent to Get Water to Staten Island
When Board of Water Supply engineers began planning how to bring Catskill water into Staten Island for the first time in 1913, they found themselves faced with a unique challenge—how would the water be carried across the Narrows—the entry to New York Harbor—into Staten Island? The biggest problem was that in the early 20th century, this harbor was one of the busiest ports in the world and the Narrows was the primary waiting point for merchant vessels awaiting Coast Guard clearance to dock at the city. As a result of all the ship traffic, there were strict shipping regulations that required any obstructions, like a water tunnel, to be 45-60 feet below low tide. One of the options the Board considered was a deep-pressure tunnel like the one used to cross the Hudson River. But the complexity and cost involved in building a deep-rock tunnel made this solution unrealistic and engineers would have to come up with an entirely new method for dealing with this design challenge.
After conducting various feasibility studies the Board decided on a novel approach—they would use a 36-inch, cast iron submarine pipeline with flexible joints capable of extending all the way from Brooklyn, across the Narrows, to Staten Island. Of the 10,620 total feet of piping that would be necessary—9,709 feet would need to be submerged in water. The first stage of the project was for workers to dig and smooth out 10- to 35-foot deep trenches where the pipe would be laid. This involved using 13-ton dredge buckets to dig the trenches and 20-ton I-beams to smooth out the bottom of the trenches.
With the method for laying the pipe resolved, the next major challenge was deciding what type of piping would be used. It was clear to engineers that all pipe joints would have to be flexible to facilitate installation. After coming up with precise standards for the amount of flexibility the pipe joints required, the Board brought in highly skilled pipe installers capable of adhering to those standards when joining the pipes. As sections of pipe were joined, workers would begin the process of placing the pipes into the excavated trenches. To do this, workers used special cradles and a floating scow that allowed the pipe to be gently lowered into the water and placed into the trenches. At intervals along the pipeline, pressure tests, which involved applying 80 pounds of air pressure to joints, were conducted to make sure there were no leaks caused by faulty joints. Despite the complexity involved in using this unprecedented piping technique, work was completed quickly and by 1915, the majority of the pipeline was laid, and the submarine pipe was connected to the land conduit, and the Narrows Siphon was put into service.
At the same time that the Narrows Siphon was being constructed, work had also started on the construction of the Richmond Conduit, a 48-inch cast iron conduit that would carry the Catskill water from a shore gatehouse located beneath Victory Boulevard to Silver Lake, a former resort area that was being transformed into a 56-acre storage reservoir called Silver Lake Reservoir. By 1917 the reservoir was filled with fresh Catskill water that was delivered to Staten Island by the Narrows Siphon.
However, despite the successful installation of the first Narrows Siphon and the Silver Lake Reservoir, water consumption on Staten Island was increasing beyond the available supply. By 1923 the Board decided it would be necessary to expand the delivery system and install a second submarine pipeline known as Narrows Siphon 2. The design of the pipeline would be similar to that used for the first Narrows Siphon, except that this time they would be laying flexible jointed, cast-iron submarine pipes. Using the same method that was perfected during the installation of the first Narrows Siphon, trenches were dug and pipe was laid, this time with the help of two floating scows that were named “Collegian” and “Champion.” At least twice a day during the installation process, a diver was sent down to examine the pipes and to caulk any leaks that were found with air-pressure tests. By 1925, the submarine pipeline and the shore connections were completed, and Siphon 2 was put into service. Together with the first Narrows Siphon, Silver Lake Reservoir was now receiving about 32 million gallons of Catskill water a day.
Additional challenges would be presented to engineers whenever repairs to the Siphons would be needed over the 40 plus years that they were in service. For example, in 1922 emergency repairs were needed to fix an 18-inch wide hole that was discovered in a section of submerged pipe located at the foot of Arrietta Street in Staten Island. In a letter to Mayor John Hylan describing the break and the subsequent repairs, Commissioner Nicholas Hayes from the Department of Water Supply, Gas and Electricity, explains that in order to remove the damaged pipe—a diver working underwater had to operate an electric torch to burn the metal away “without any hood or other protecting device to keep the water away from the torch.” Although the repair was successful, Commissioner Hayes goes on to say that the break was “the most difficult repair job that the Department had ever undertaken.”
Later, in 1938, when a section of Narrows Siphon 2 would sustain similar damage, engineers were able to make the actual repairs without having to work underwater. Because there were now two siphons, it was possible to shut down the damaged one while the first siphon continued to supply water to the borough. As a result, workers were able to excavate the damaged section of pipe, remove it by burning it off with an oxy-hydrogen torch, and then replace it with a brand new section of pipe. The entire repair process was so extraordinary that it was featured in a February 15, 1939 issue of Water Works Engineering.
By 1968, the completion of the Richmond Tunnel, a five-mile long pressure tunnel that connected Staten Island to City Water Tunnel No. 2 in Brooklyn, increased delivery capacity to 300 million gallons of water a day and rendered both Narrows Siphons obsolete. However, both siphons are currently active in a stand-by mode and serve as a back-up to the Richmond Tunnel. Today, however, plans are underway to replace the two siphons as the back-up water supply for Staten Island, as DEP works with the Port Authority, the Army Corps of Engineers and the Economic Development Corporation to dredge that area of the harbor. Meanwhile the Silver Lake Reservoir would continue to serve Staten Island until 1970 when it too was replaced because of the ongoing water loss caused by ground seepage in the reservoir. The reservoir replacement came in the form of two of the world’s largest, underground water-storage tanks, capable of holding 100 million gallons of water. Subsequently, the Silver Lake Reservoir, although not used as a potable water supply source, is still an active part of the water distribution system and remains a DEP asset.