Wachusett Aqueduct

Although it looks like a bridge, this structure carries a covered aqueduct tunnel with an inside profile of 11′ x 12′ (3.4m x 3.6m) capable of carrying about 3,000 gallons per second (11,000 l/s) of water. Known as the Aqueduct Bridge or the Assabet River Bridge, it is a 400′ masonry arch bridge carrying the Wachusett Aqueduct across a millpond on the Assabet River in Northborough, Mass. Construction was by the Metropolitan Water Works (which was succeeded by the Metropolitan District Commission and today by the Massachusetts Water Resources Authority) under Thomas Franklin Richardson, engineer of the Dam and Aqueduct Department. A report by the Massachusetts Historical Commission suggests that the appearance is slightly deceptive: under the stone facing, steel beams may have been used as part of the structure. Although it’s hard to judge scale in this photo, the two-lane road alongside the river runs through one of those arches, with a 10′ (3m) clearance.

The Wachusett Aqueduct was constructed 1896-1898 as part of the larger project to create the Wachusett Reservoir, at the time the world’s largest public water supply reservoir (7 square miles or 18km²) , to serve Boston’s ever-growing need for drinking water. Most of it is underground, but for this crossing the architects chose to use a bridge. The aqueduct was replaced with a newer one in the 1960’s, which crosses the river in a siphon; a curved tunnel that loops below the river. The original aqueduct was upgraded in 2001 to serve as a backup during construction of a new aqueduct near Boston. And this proved useful in 2005 when a fitting on the new aqueduct gave way, and the backup was needed for several days while repairs were made.

I’d first run across this structure by accident, many years ago when I took a wrong turn. At the time I thought it was an abandoned rail or road bridge because there is vegetation growing on the top. That’s apparently grass growing in a century’s worth of wind-blown dirt along the edges. I’ve wanted to get back there on a sunny day and take a picture for a long time, but the idea and the opportunity never came together before.

The photo came out fairly well. The stark summer sun is high enough to create shadows between the courses of stones, which helps to give it definition. The white lime (calcium) deposits that have coated the stone over the years are an interesting contrast to the green of the vegetation. The algae-choked river isn’t as nice as a clean one would be, but from other photos I’ve seen that only happens over the winter (and most of those photos were of the shaded side). Revisiting this in the late fall or early spring may be worthwhile; see this blog for an early Spring  (March 2011) photo and a link to an article (PDF) on the aqueduct. Also see the Spring 2005 (PDF) issue of Downstream for a history of the reservoir with some construction photos of the dam.

The photo was taken last weekend, at ISO 200, f/11, 1/125-second exposure, with the lens set to 73mm. I also used a circular polarizing filter (for the first time) to see if this would help improve photos taken in hazy weather, which it did seem to do. Since it takes away roughly two stops of light, I’m not going to use this too often. But my initial impression is that it improves well-lit structures, so I expect I will use it again. Processing was very minimal for this image. It was cropped slightly to remove some foreground vegetation. It also had the Exposure black point and Highlights & Shadows settings adjusted slightly to restore detail in the darker areas, with a touch of added vibrancy on the Enhance setting and the usual Edge Sharpening.


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