Arboriculture & Urban Forestry 33(6): November 2007 Arboriculture & Urban Forestry 2007. 33(6):435–439. 435 Research Note New Diagrams and Applications for the Wire Zone–Border Zone Approach to Vegetation Management on Electric Transmission Line Rights-of-Way Benjamin D. Ballard, Kevin T. McLoughlin, and Christopher A. Nowak The wire zone–border zone (WZ/BZ) approach to vegetation management on electric transmission line rights-of-way (ROWs) was formally introduced by Drs. Bramble and Byrnes in the mid-1980s (Bramble et al. 1985, 1986). It is a site- explicit way of dividing the ROW width into three distinct management zones from edge to edge: the border zone, the wire zone, and another border zone (Figure 1). In this clas- sical WZ/BZ approach, the ROW vegetation is managed differently in the two basic zones, purportedly to optimize the safe and reliable transmission of electricity. Herb–grass–forb cover types (low-growing vegetation), which may include some very short woody shrubs (oftentimes all woody shrubs are excluded), are promoted in the wire zone; whereas shrub– short tree cover types (taller woody vegetation) are allowed to grow in the border zones (Ballard et al. 2004; Yahner and Hutnik 2004). The WZ/BZ approach is also touted to ensure that other values are consistently, predictably produced on ROWs, including aesthetics, wildlife habitat (as exemplified by Bramble, Byrnes, and Yahner’s Pennsylvania State Game Lands 33 research; e.g., Bramble et al. 1985, 1986; Yahner et al. 2004), biodiversity, and lower long-term vegetation man- agement costs. Recently, the U.S. Federal Energy Regulatory Commission (FERC) and the North American Electric Reliability Corpo- ration effectively endorsed the use of the WZ/BZ for manage- ment of ROW vegetation (www.nerc.com/∼filez/standards/ Vegetation-Management.html; Standard FAC-003-1) by rec- ognizing the American National Standards Institute (ANSI) A300 Tree Care Operations standards as an “industry best practice” (the WZ/BZ approach was also presented as a Best Management Practice in the Final Vegetation Management Report to FERC on the 14 August 2003 blackout; CN Utility Consulting 2004). Promotion of the WZ/BZ approach is clear in the ANSI A300 Part 7-2006 Integrated Vegetation Man- agement standards (ANSI 2006). In the ANSI standards and other recent portrayals of the WZ/BZ approach (Nowak et al. 2002; Nowak and Appelt 2002; Ballard et al. 2004; Yahner et al. 2004), the original Bramble et al. (1985, 1986) diagram was commonly used as a basis for both describing and illus- trating the approach (Figure 1A). This original WZ/BZ dia- gram was useful for introducing the initial concept, but our recent efforts to use the WZ/BZ approach in research, devel- opment, and technology transfer identified two critical short- falls: 1) the diagram was not to usual, operational scale, be- cause the two border zones (approximately 60% of ROW width in the Bramble et al. diagram) were much larger than is normal for operating ROWs, resulting in a depiction of an unusually wide ROW; and 2) the two-dimensional cross- section of the ROW oversimplified real-world ROW condi- tions, in which WZ conductor-to-ground distances vary as a function of conductor sag (position between tower structures) and sway and site topography. Inaccuracies and oversimpli- fication in the original Bramble et al. diagram can affect how the WZ/BZ approach is interpreted and implemented. We have redrawn the WZ/BZ diagram to be more consistent with actual field operations (Figure 1B). We have also fashioned representative plan and profile views to produce a more re- alistic and spatially explicit, three-dimensional illustration of ROW conditions in relation to WZ/BZ boundaries (Figure 2) so as to provide a more flexible and practical interpretation of the WZ/BZ approach for application to modern, integrated ROW vegetation management. The plan and profile views (Figure 2), when used in con- junction with the cross-section view (Figure 1B), provide a three-dimensional image of a ROW, which demonstrates that not all of the ROW area under the conductors needs to be treated as “wire zone” (i.e., to exclude all woody vegetation). For example, on level sites, the conductors are closer to the ground at midspan (conductor sag and sway are a concern), but ROW areas directly under the conductors and closer to tower structures may provide sufficient ground-to-conductor clearance to permit retaining typical “border zone” vegeta- ©2007 International Society of Arboriculture
November 2007
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
