Over the course of my career, I’ve had the chance to work, and take photographs, at several really interesting places. Among my favorites are those that are focused on what I call, for lack of a better term, water resource engineering. In less-fancy terms, that means dam, canals, hydroelectric sites, and such. Of these sites, perhaps the most amazing is the New Croton Dam, just north of New York City. In 2010 and 2011, I was invited to team with the Public Archaeology Facility to carry out a study of the dam, and its various components, in order to assess the impact of some changes that the owner of the dam, the New York City Department of Environmental Protection, had proposed. It wasn’t a photography job, but I couldn’t resist bringing the large-format camera with me and getting some HAER-level photographs of this incredible structure.
New Croton Dam-lower valve chamber roof
The New Croton Dam is the jewel in the crown of the vast, sprawling water supply system for New York City. The needs for fresh water for the City began growing dramatically by the early 19th century. The City fathers, recognizing that they couldn’t provide fresh water for the City locally, began looking in the 1820s and 1830s to the rivers north of the City. The result was what as known as the Croton Dam, designed by the engineer John Jarvis and located about six miles upstream of where the Croton River joins the Hudson. Built in 1842, the masonry dam was 57 feet high and fed water to what remains known as the Croton Aqueduct, which originally delivered water to a massive brick reservoir at 42nd Street and 5th Avenue.
The Croton Dam was unable to keep up with New York City’s growing demands for water, and in the 1880s the City began planning for a new dam. The result is the massive New Croton Dam, truly one of the great engineering masterpieces of late-19th century America. The dam spans a relatively narrow valley about three miles downstream of the original Croton Dam. This valley has a gentle earthen slope at the south end and a steep rock wall at the north end. The overall design of the New Croton Dam complex is fascinating. The masonry dam extends from the south end of the valley, and ends just short of the north end at a unique curved, stepped spillway that extends from the north end of the dam, and then curves sharply to the east and runs upstream, into the impoundment, parallel to the rocky north wall of the valley before tying into the north wall. The spillway allows water to flow through the narrow channel between it and the rocky wall of the valley, creating a beautiful cascade. An arch bridge then spans the channel, to connect a road at the north side of the valley to the dam, which has a two-land road across the top. This road, unfortunately, is now closed in the post-9/11 world.
While this was not a photography job, I had my camera with me, and took several photos on my first visit in 2010. I returned for some follow-up work in 2011, and had a chance to take some photographs inside one of the gatehouses, which is actually a part of the dam where the bridge meets the dam at the north end. This gatehouse controls the flow of water out of the impoundment, which allows the impoundment to be drawn down if necessary. The client ended up not needing the photos, so I’ve included them in the gallery above.
This dam is seriously massive, and is incredibly imposing as you drive toward it from the downstream end. For a more technical description, here’s what I included in the report:
The main portion of the New Croton Dam is the masonry non-overflow section that runs north and south across the Croton River Valley. The masonry non-overflow section extends 1168 feet from the south bank of the valley to the spillway channel, and is constructed of massive granite blocks of approximately three cubic yards each. The base of the dam is founded on bedrock which lies 131 feet below the bed of the Croton River, and is 208 feet thick at the base. The upstream face of the dam is vertical, while the downstream face of the dam slopes as it moves to the top, where the dam is 18 feet thick. The dam rises a total of 297 feet from its base on bedrock, and the top of the dam is 166 feet above the bed of the Croton River. The dam is surmounted by a two-lane paved road that is 20 feet wide and that is protected on both sides by a heavy metal railing.
Two gatehouses are integral with the dam, and serve different purposes. Gatehouse No. 1 is located at the south end of the dam on the downstream side, and is set within a portion of the dam that curves outward toward the downstream side. The purpose of this gatehouse is to control the flow of water through the Old Croton Aqueduct that runs along the south side of the valley, below the new impoundment, and to allow water into the Old Croton Aqueduct at the new dam. The substructure measures approximately 55 feet high and contains four water chambers. Water from the Old Aqueduct enters into the southeast chamber, through flows through two gated sluice-ways into the southwest chamber. Water then flowed through a 510-foot long conduit back to the Old Aqueduct. Water can also be drawn into Gatehouse No. 1 from the New Croton Dam impoundment through the northeast chamber, with inlets that can be closed with stoplog gates; water can then pass through sluice gates into the southeast chamber and thus into the Old Croton Aqueduct. The hoisting machinery for the sluice gates is located in a vault chamber above the lower water chambers; the redesign of the dam in 1901 allowed for both of these to be below the level of the dam. The top of the gatehouse is level with the top of the dam, and is protected by modern concrete panels.
Gatehouse No. 2 is located at the north end of the dam where it meets the spillway. The purpose of this gatehouse is to serve as a blow-off valve to draw water from the reservoir as needed. This gatehouse consists of two components: an upper gate chamber and a lower valve chamber. The upper gate chamber is flush with the top of the dam, and extends approximately 50 feet into the impoundment from the upstream face of the dam. It controls the flow of water into three 48-inch blow-off pipes, each with its own intake opening on the upstream face of the upper gate chamber. Water from these inlets is drops down to valves in the lower chamber and is protected by gate valves that are operated a by a long stem extending down from the upper gate chamber floor. Gatehouse No. 2 has remained essentially intact from its original design.
The research for this project was as fascinating as the dam itself. The City’s Department of Environmental Protection has its own archives, which is an amazing treasure trove of engineering history. It was an honor to be able to help, in some small way, to take care of this amazing piece of American engineering.
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