Temple Tackles Road Problems With High-tech Materials
Mitigation in New Hampshire
When a heavy rain drenches southwest New Hampshire's Monadnock Mountain range, much of it finds its way downhill to the town of Temple. The usually placid streams fill with runoff and grow wider than their banks, pushing against too-small culverts and roadways. The high water generally leaves behind washed out gravel or sections of roads.
But each year, the number of road washouts gets smaller. For the last 20 years, one road at a time, the town's road agent, public works crew and town select board have reduced road damage by taking the initiative to rebuild stronger. New materials and technical assistance have helped in their mitigation endeavors, as well as federal funding provided during recovery after declared disasters, according to Road Agent Timothy Fiske.
Technical assistance has come by way of the Technology Transfer Center, or T2 Center as it is commonly called, which manages the state's Local Technical Assistance Program (See related article on LTAP).
The T2 Center gave Fiske his first experience with geotextiles back in 1988. Geotextiles are permeable fabrics, engineered to control drainage. When used in association with stone and soil, they have the ability to separate, filter, reinforce, protect, or drain. Geotextiles often yield benefits in public works projects involving roads, embankments, retaining structures, bank protection and coastal engineering. The center recommends working with engineers familiar with geotextiles when designing road mitigation projects.
Advisors at the T2 Center wanted to demonstrate how geotextiles help drainage when used in the right place and were looking for a volunteer road agent with a muddy road. Fiske volunteered a narrow, boggy gravel road that turned into foot-deep mud every spring. The demonstration involved help from six different town road agents who then learned how to install the material for that particular problem. Fiske said he hasn't had a problem with the road since.
Fiske became a believer in using geotextiles after that first experience and has continued to use different types of geotextiles in road repair when possible. For one particularly pesky road that Fiske remembers washing out 10 times in a dozen years, he worked with a FEMA mitigation technical specialist, Richard Downer, when repairing it in 2005.
At the outset, Fiske had two difficult situations to work with at the site on Fish Road: a stone culvert with historic value and the need to obtain funding for the improvements. The repair of the road was eligible for FEMA Public Assistance funds because the area was included in a federally-declared disaster. A requirement for receiving federal funds is that the applicant must comply with federal, state and local laws that regulate environmental and historic preservation.
Because of the historic nature of the culvert, Fiske had the project reviewed by the state historic preservation officer. The historic character of the culvert would be retained and preserved with little visual impact from the repair by rebuilding with the original stonework. And to help prevent continued damage to the culvert in future flood events, they were able to add a cement culvert beside the stone culvert, engineered to be a secondary flow-through when floodwaters backed up behind the stone culvert.
But Fiske wasn't finished with the job yet. In addition to a larger opening for floodwaters to flow through under the road, the road itself needed help to stay put in the event floodwaters would overtop it. Using geotextiles to hold the gravel roadbed in place and reduce erosion seemed the right option.
First, the roadbed was shaped to confine the overflow to the armored area by making a long shallow depression in the road over the culverts. Fiske and his road crew then installed 400 square feet of geocell on top of the roadbed at that point. The geocell material has cells like a honeycomb and the cells are filled with stone or gravel. The intent is that when water runs over the road, rather than separate pieces of gravel or stone for the rushing water to carry away, the filled geocell material acts as a whole unit to hold the roadbed in place.
"We stretched the geocell over the roadbed, pinned it in place and filled it with crushed stone," explained Fiske. "Then we overlaid it with 3 inches of crushed gravel."
The extra step of installing the geotextile material added $2,134 to the project that had a total coast of $7,734. FEMA Public Assistance funds covered 75 percent of the cost. The road was tested in the 2007 April nor'easter. Even though floodwaters overtopped the road, it suffered only minimal loss of gravel from the road edge. Fiske estimated to fix the road in previous washouts it cost $1,400 to repair the culvert and haul in gravel.
"With the mitigation money, you spend it once and fix the problem right," said Fiske.
Last Modified: Wednesday, 27-Feb-2008 10:01:00 EST