80 Appleton: Designing and Implementing Utility Line Arboreta Designing and Implementing Utility Line Arboreta Bonnie L. Appleton Abstract. In the United States, a significant conflict exists between overhead utility lines and inappropriately tall trees planted in or near line easements. A major goal of Virginia, U.S.’s Municipal Tree Restoration Project is the establishment of utility line arboreta in multiple state locations as a way to evaluate, showcase, and promote trees compatible with overhead utility lines. Three different utility line arboreta models have been developed that can be replicated anywhere internationally to deal with this important infrastructure conflict. A stepwise list of considerations and potential funding sources for developing utility line arboreta is provided, as well as a comparison of the advantages and disadvantages of the three described utility line arboreta models. Key Words. Electrical power; line clearance; Municipal Tree Restoration Project (MTRP); power outage; species selection; utility-compatible trees; utility easements; utility pruning; utility right-of-way management. Although most people take for granted our generally uninter- rupted delivery of electrical power, in many areas of the United States there is a major and potentially disastrous con- flict between overhead utility lines and inappropriately tall trees planted in or near line easements (Appleton 2004). Trees can cause power outages by direct contact with lines, as they or their branches fall on lines or damage electrical equip- ment or support structures, or by electrical arcing between tree parts and nearby high-voltage conductors (U.S.–Canada Power System Outage Task Force 2004). Two recent occurrences underscore this tree–electric line conflict. On 14 August 2003, an electric power blackout oc- curred that affected large portions of Ontario, Canada, and the midwestern and northeastern sections of the United States. In some parts of the United States, power was not restored for 4 days. A final report on the blackout stated: From 15:05:41 EDT to 15:41:35 EDT, three 345-kV lines failed with power flows at or below each trans- mission line’s emergency rating. These line trips were not random. Rather, each was the result of a contact between a line and a tree that had grown so tall that, over a period of years, it encroached into the required clearance height for the line…Each of these three lines tripped not because of excessive sag due to overloading or high conductor temperature, but because it hit an overgrown, untrimmed tree (U.S.–Canada Power Sys- tem Outage Task Force 2004). Shortly thereafter, on 18 September 2003, Hurricane Isabel caused major electric power outages along the mid-Atlantic coast. This power outage affected more than 6.5 million cus- tomers at the storm’s peak, five times the number of outages caused by Hurricane Andrew; until the 2005 season, it was ©2006 International Society of Arboriculture the most costly of all hurricanes (Department of Energy 2003). According to Dominion Virginia Power, one of the nation’s largest producers of energy, Hurricane Isabel was the worst storm in the company’s 100-year history (Dominion Virginia Power 2003). In southeastern Virginia 94% of cus- tomers lost electrical service (which in some cases took 2 weeks to be restored); 84% of customers in northeastern North Carolina lost power. Falling limbs and whole trees torn from sodden ground were in great part responsible for 62 downed transmission lines (1,600 miles of high-voltage lines), 1,150 disrupted primary distribution circuits, 2,311 broken utility poles, 3,899 snapped cross arms, and 7,363 spans of downed power lines. Every year, North American utilities spend an estimated $2 to $10 billion for vegetation management along utility lines (Guggenmoos 2003). Vegetation management ranges from line-clearance pruning and whole tree and tree debris removal along all lines to the application of herbicides to kill or retard growth of any vegetation type in transmission line rights of way. Preventive maintenance generally involves conducting these activities on regular, predetermined cycles depending on line location, vegetation (including trees) height and growth rate, and local regulatory reliability and clearance requirements. Corrective maintenance is performed on an as- needed basis (often related to wind and ice storms, hurri- canes, tree-related outages, and so forth). Although line clearance may result in trees deemed aes- thetically unacceptable, in the United States not only has legal precedent established that utilities have the right to prune and remove trees that interfere with necessary and rea- sonable utility operations (Merullo and Valentine 1992), but utilities are legally required to do so (ANSI 1997). Although numerous options, including burying utility lines and apply- ing tree growth regulators, exist to deal with this conflict, one
March 2006
| 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
