Friday, March 25, 2011

How Tall Could the Towers Be?

Northern Pass has now embarked on a publicity campaign that "visualizes" towers in landscape settings. Various statements about tower heights accompany these "simulations." There are discrepancies between the document of record, the Presidential Permit application (PPA) filed in October 2010, and recent  publicity statements. Let's review the document of record first and then look at the publicity material to see how high the DC towers could be. (AC towers from Franklin south are not discussed here.) This is Part 1 in a series. Coming next in Part 2: How wide could the ROWs be?

What Northern Pass said in the Presidential Permit application about DC tower heights
For the portion of the Project running from the international border to Franklin, New Hampshire, Northern Pass proposes to construct a single circuit ±300 kV HVDC above-ground transmission line that will be mounted on structures ranging from approximately 90 feet to 135 feet tall. (p. 9)

For both the monopole and lattice configuration, the horizontally configured structures would be approximately 90 feet in height, and the vertically configured structures would be  approximately 135 feet in height. [Ftnt. 4] (pp. 11-12)

Structure heights are typical for a straight, level stretch of land. Actual structure heights will vary, and may be greater in height (e.g., highway crossings), based on topography, span length and the line layout. (footnote 4, p. 12, emphasis added)

To summarize, in the document of record, Northern Pass states that horizontally configured DC towers (energized conductors side-by-side) will be "approximately 90 feet"; that vertically configured DC towers (see illustration below) will be "approximately 135 feet"; but both "may be greater in height" than approximately 90' and approximately 135'. OK . . . .what is "approximately 90 feet"? 80 feet? 100 feet? What is "approximately 135 feet"? 150 feet? And what is "greater in height" than approximately 135 feet, which might actually be 145 feet or 150 feet? 180 feet?

How tall could the DC towers be? According to the PPA, the sky's the limit. 

What Northern Pass is Saying Now in Promotional Statements

In its Project Journal posted on March 25, 2011, however, Northern Pass tells a different story about maximum tower height:

Taller structures (up to 135 feet) will only be used along the route when necessary:
  • To span larger rivers and roadways;
  • To account for changes in terrain being spanned by the line, and maintain a consistent distance between the transmission wires and the ground; and
  • In select areas in the existing ROW where the ROW is constrained and cannot be expanded to a width necessary for shorter structures.
Which do you believe: the document of record (PPA) that, in the small print of footnote 4, places no limit whatsoever on DC tower height, or the promotional "Project Journal," which limits tower height to 135'?

Keep this in mind as you see tower simulations that Northern Pass will place in newspapers and elsewhere over the next week or so. Also keep in mind that simulations may show you towers out of context, not in a clearcut ROW anywhere from 150' to 400' wide, or show you towers from advantageous perspectives. Note the small print--"for illustrative purposes only, based on preliminary engineering." Keep all this in mind and you will understand why the DOE has been asked to require a professional, independent, third-party visual simulation that is not for Northern Pass's "illustrative purposes" but for the purposes of accurately informing landowners and others what the visual impact of Northern Pass towers will be.

Oh, by the way, Exhibit B, sheet 2 of the PPA depicts a 140' tower (64' + 76'). Maybe that's what "approximately 135 feet" means in the PPA. But no matter, the sketch is just "preliminary--not for construction." The sky's the limit. 

HVDC line (center) flanked by two HVAC lines on the National Grid ROW, Haverhill area

National Grid HVDC tower on Rte. 302 near Bath and Swiftwater NH

Coming next: How wide could the ROWs be? (Preview: as wide as necessary.) And, what tower heights are in store for the narrow ROW in the WMNF? (Preview: the sky's the limit.)