The following is an excerpt from the Town of Antrim's Master Plan created in August, 2001.
CONSERVATION AND PRESERVATION
This section represents an on-going effort by the Antrim Conservation Commission, in conjunction with the Antrim Planning Board and the Antrim Historical Society to update portions of the Open Space & Recreation and Land Use section of the 1985 Master Plan. The creation of the Conservation and Preservation section of the Master Plan is authorized by NH statute RSA 674:2, which states “A conservation and preservation section . . . may provide for the “preservation, conservation, and use of natural and man-made resources”.
The purpose of this section is multifold: first, it is intended to describe the natural and man-made features of Antrim that are important and thought to have significance. This information is intended to enable better-informed decisions as to the development of certain areas of Antrim. Second, it intends to supply the residents with information about sensitive areas, natural areas, natural resources and important natural and/or man-made features which may need special protection. An additional benefit of supplying these data is that the public may become better educated about the significance, sensitivity, and value of the natural and man-made environment. It is hoped that this knowledge enables people to think about the appropriateness (or inappropriateness) of using certain lands for certain uses. For example, in the past, it was
generally thought that wetlands were lands of poor value and should be filled in. Today, it is widely recognized that wetlands provide valuable storage retention areas for the attenuation of flood waters, as well as important ecological niches and habitat for numerous species which are beneficial to the natural environment and man alike. It is the opinion of the Conservation Commission that the Town’s present and future growth needs be well planned, balanced growth, which is manageable and sustainable.
Future actions made on the basis of the information in this section may be implemented through a variety of ways, which will be discussed in more detail later. Courses of action may include but not be limited to such things as amendments to the zoning ordinance, or possibly design/development standards written into the Site Plan Review Regulations to address specific concerns.
This Plan is a result of an evaluation of the natural and man-made resources in Antrim, as identified by members of the Conservation Commission, the Planning Board, the Historical Society, students at Great Brook Middle School and individual town residents. The concepts and ideas presented herein came from numerous discussions and forums including, and not limited to, the town-wide profile entitled “Antrim Next” held in May of 1998. The features identified and described herein are also illustrated on maps, some of which are included in this report, while other are on file at the Town Offices.
This discussion of natural features looks at topography, geology, water resources and trails and protected lands.
The Town of Antrim is quite hilly, with much of the town classified as having greater than 15% slopes. Two large north-flowing rivers – the Contoocook and the North Branch Rivers – transect the town. The majority of the topographic relief occurs in the western and northern sectors of town.
Mountains and Hills in Antrim
Mountains Elevation (ft.) Hills Elevation (ft)
Bald Mountain 2,030 Goodhue Hill 1,620
Gibson Mountain 1,330 Holt Hill 1,370
Riley Mountain 1,440 Meetinghouse Hill 1,370
Robb Mountain 1,820 Patten hill 1,390
Willard Mountain 1,920 Tuttle Hill 1,760
Windsor Mountain 1,450
Source: United States Geologic Survey
Slope is a major factor when reviewing the town’s available landmass for development. Slope of the land is defined, as the change in vertical distance (height) over a horizontal distance i.e., 10 feet over 100 feet equals a 10% slope. The Antrim Town Slope Map shows four slope classes; these are:
Flat-Lying Slopes: These are slopes that would be described as flat to gentle slopes between 0 and 8%. These are generally the types of slopes that are most favorable to development because of the ease of site construction and development. Development in flat slope areas may be hindered by restrictions due to wetlands, poor soil/bedrock conditions, floodplains or Shoreline Protection areas.
Moderate Slopes: These are slopes that fall between 8 and 15%. These slope areas can be developed but at a greater cost. Costs due to steeper slopes are predominantly tied up in site design and initial construction.
Steep Slopes: These are slope areas that fall between 15 and 25%. These slope areas cannot be developed at this time without extraordinary means.
Excessively Steep Slopes: These are slope areas that are greater than 25%. These slope areas are generally considered not feasible for development, due to the costs of site work.
The bedrock geology of the town is the solid rock mass that underlies the surficial deposits frequently found covering the landmass. Both metamorphic and igneous rocks underlie the town of Antrim. According to the 1997 Bedrock Geologic Map of New Hampshire, three major rock types may be found in town. They are in accordance with their geographic volumes (greatest to least) the Kinsman Granodiorite, the Spaulding Tonalite, and the Littleton Formation.
The Kinsman Granodiorite was formerly known as the Kinsman Quartz Monzonite of Billings (1955). It is described as a foliated granite, Granodiorite and Tonalite with minor amounts of quartz diorite. It characteristically possesses large potassium feldspar megacrysts and locally abundant garnet zones. It is an igneous body that is known as the Cardigan Pluton of the New Hampshire Plutonic Suite. The Cardigan Pluton of the New Hampshire Plutonic Suite is lower Devonian in age and has been dated approximately between 410 and 420 million years old.
The Spaulding Tonalite was formerly known in older literature as the Spaulding Quartz Diortie of Fowler-Billings (1949). It is presently described as a weakly foliated to non-folitated, spotted biotite diorite, tonalite, Granodiorite and granite. It is the dominant igneous rock type on the northeast side of town. It is known as the Antrim Pluton of the New Hampshire Plutonic Suite and its age is lower Devonian, just slightly younger than the Cardigan Pluton.
The Littleton Formation is an undivided lower Devonian metamorphic rock body, which forms much of Riley Mountain on the northeast side of town. The Littleton Formation is comprised of gray, coarse-grained metasedimentary rocks that can be described as mica schist.
The soils on the bedrock in town are the result of erosion of the local bedrock or the result of glacial, lacustrine (lake), recent alluvial (stream), colluvial (slope) and pluvial (swamp) mechanisms forming the soil rind on the bedrock. The majority of the soils in town are the result of the late Wisconsinan glaciation (last glacial age). The soils are either ice contact deposits such as (subglacial) glacial till or eskers, ice terminal deposits such as kames, or glacio-lacustrine deposits, such as deltas, and lake bottom deposits, which are relic to Glacial Lake Contoocook. Glacial Lake Contoocook was a large regional lake that was dammed by glacial ice on the north and topographic highs to the east, south and west. Glacial Lake Contoocook occupied much of the Contoocook Valley below approximate elevation 870 in Antrim.
The Town of Antrim is gifted in the number and quality of its water resources. Described below are watersheds/riverbasins, water bodies, wetlands, aquifers, and floodplain areas in Antrim.
A watershed is an area in which all the land drains to a particular common point or body of water. When dealing with a body of water, it can be thought of as being synonymous with a drainage basin.
Besides acting as collection areas for surface water bodies, they also function as holding areas for floodwaters and seasonal high waters. In addition, they serve as recharge areas and discharge points for groundwater. Groundwater recharges surface water resources, as well as water wells during dry summer months.
The surface waters of rivers, streams, lakes, brooks and ponds are not only collection points for water but are also sinks for collecting pollution. There are two main categories of pollution: point source pollution and non-point source pollution. Point source pollution is pollution in which a specific source can be identified. An example of a point –source type of pollution would be a sewer pipe discharging directly into the water.
Non-point source pollution is pollution that is caused when water flows overland or through the ground, picks up pollutants and transports them away from the source and deposits them elsewhere, in surface or ground waters. Surface run-off can be considered a non-point pollution source because it can pick up many types of pollution on its way to a waterway. Several examples of specific pollution types that can enter our waterways through storm drains are as follows: sediments, fertilizers, pesticides, vehicle fluids (leaking oils, fuels and anti-freeze), litter, household hazardous waste, and paint, just to name a few.
Antrim falls entirely within the Contoocook River Watershed, which is a part of the Merrimack River Basin. There are four main watersheds in Antrim: the Contoocook River, the North Branch of the Contoocook River, Great Brook, and Cochran Brook. The Contoocook River flows approximately 70 miles from Poole Pond in Rindge north to Concord, where it flows into the Merrimack River. Its total drainage basin amounts to 766 square miles. Antrim’s portion is but a small part of this total area, located approximately at its midpoint. All of Antrim’s surface water drainage eventually flows into the Contoocook River.
The North Branch is a major tributary of the Contoocook River and which flows northerly from Highland Lake in Stoddard to its confluence with the Contoocook River in Hillsboro, just north of the Antrim town line. Both of these rivers were placed in the New Hampshire Rivers Management and Protection Program in June 1991.
Surface drainage for Great Brook first initiates from the eastern slopes of the western hills (Tuttle, Holt and Patten Hills, and Willard Mountain), which then flows into Gregg Lake. The outlet from Gregg Lake is the first time the designation of Great Brook is used. It flows easterly approximately two miles from Gregg Lake into the main village section of town. Here it turns southerly and is dammed to form the Mill Pond, which closely parallels Main Street. The Summer Street Dam forms the Mill Pond. From this outlet, it continues southerly approximately ¼ mile where it turns easterly again and enters the Contoocook River. Cochran Brook’s headwaters flow into Campbell Pond. From Campbell Pond the brook flows south-southeasterly approximately three miles to the Contoocook River.
The following are a list of significant lakes and ponds in Antrim with a brief description of the recreational and other uses of each waterbody listed.
Franklin Pierce Lake is approximately 519 acres in size. The southern third of the lake is in Antrim, while the main body and the Harriman Electric Power Dam are in the town of Hillsboro. It is a warm water fishery. Recreational uses include fishing, water skiing, boating, sailing, swimming and bird watching. There is, at present, limited public access in the town of Antrim to this lake.
Gregg Lake is approximately 195 acres in size. It is a moderate warm water fishery. Recreational uses include fishing, picnicking, water skiing, boating, sailing, and bird watching. Public access is adjacent to the Antrim town beach. According to RSA 270:74-a – “Skicraft operation at the lake is restricted to No Greater Than Headway Speed in the portion starting in the area known as the Meadows and extending to the area known as the Narrows, extending to a point approximately 500 feet south of Camp Birchmere effective 8/30/89”. According to SAF-C 402.261-“(a) Motorboats shall be limited to 150 HP or less on Gregg Lake and, (b) All water-skiing on Gregg Lake shall be in a counter-clockwise direction at all times”.
Willard Pond is approximately 96 acres in size. It is an excellent cold water fishery. It is part of the dePierrefeu-Willard Pond Wildlife Sanctuary. Fly fishing, hiking, and bird watching are the main recreational uses of the sanctuary. Public access is provided for boats. According to RSA 270:82-“No person shall use or operate any boat equipped with a petroleum powered motor on Willard Pond in Antrim”.
Campbell Pond is approximately 17 acres in size. It is the former water supply and present back up water supply for Antrim.
Lilly Pond is under 10 acres in size. Hiking and bird/wildlife watching are the main recreational uses of the pond. Public access is by foot trail through a series of formal and informal easements.
Rye Pond is approximately 13 acres in size with portions of the pond in the towns of Antrim, Nelson, and Stoddard. It is a warm water fishery with limited public access.
Steele’s Pond is approximately 36 acres in size. It provides the water source for a small hydro power plant, whose generated electricity is sold to Public Service of New Hampshire. There is no recreational activity at this Pond, other than some limited fishing off of the bridge.
A wetland is defined by the New Hampshire Department of Environment Services (DES) Wetlands Bureau as “…an area that is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal conditions does support a prevalence of vegetation typically adapted for life in saturated soil conditions.”
“Wetlands” is the collective term for land that serves as a transition zone between surface water and upland sites. Wetlands can be bogs and peatlands, fresh marshes, salt marshes, wooded swamps, and riparian areas.
There are several methodologies a town can use to define wetlands. These methods generally fall within the U.S. Army Corps of Engineers (USCOE) or the U.S. Department of Agriculture, Natural Resource Conservation Service (formerly Soil Conservation Service) definitions. The USCOE definition is based on fourteen functional values associated with wetlands; these include wildlife habitat, flood control, groundwater use, nutrient retention, educational potential, water-based recreation and historic value. This is the definition most often used for site specific work. The USDA method categorizes soils as being either very poorly drained or poorly drained. This is the method utilized as the basis for generalized planning.
In Antrim, wetlands constitute about 2,475 acres (11%), out of the total land area of 23,125 acres. They are distributed fairly evenly around town, consisting primarily of small pockets or areas adjacent to streams. There are, however, a number of significant and large wetland areas in town. Some of these wetlands are listed here, but this list is not all inclusive: Meadow Marsh, Cochran Swamp, Great Cedar Swamp, Liberty Farm Swamp, Salmon Brook Swamp, and bottom land areas adjacent to the drainage in town (i.e. including but not limited to the Contoocook River, Great Brook and the North Branch).
Aquifers are defined as a body of rock or soil formation that is sufficiently permeable to conduct groundwater in sufficient volumes to be economical. They are found where saturated layers are permeable and the storage and transmission of water can take place. Aquifers are generally supplied through precipitation. Precipitation infiltrates the ground through the aerated zone where impurities may be filtered out of the water. The water then moves to a saturated zone (aquifer) where the pore spaces between soil particles are filled by water. Surface water, springs, wetlands, lakes and streams are generally discharge points for aquifers.
Aquifers of medium to high potential occur in Southwest New Hampshire generally as stratified deposits of sand and gravel (known as unconsolidated deposits). Coarse-grained stratified deposits (sand and gravel) have abundant pore space to store water, and pore space may amount to as much as 30% of the total volume of the deposit. Consequently, these stratified deposits of sand and gravel, if saturated, can be good sources of medium to high-volume aquifers.
Bedrock aquifers (known as consolidated deposits) are generally a less-productive water source. However, when a saturated layer of sand or gravel overlies fractured bedrock, its ability to transmit water increases substantially. Due to the lesser volumes needed for individual domestic use and the ability to isolate the bedrock aquifer from surface activities, they are usually adequate for individual domestic wells.
In contrast, a glacial till aquifer will yield less water than a stratified drift aquifer. The physical characteristics of the till, its variable grain size, density, and compacted nature cause the porosity to be considerably less than the stratified drift type aquifer. Therefore, the transmission and ability to store water is greatly decreased in the glacial till type of aquifer.
Groundwater in saturated soils is generally vulnerable to pollution because surface contamination can infiltrate directly into it. It is possible to trace the source of pollution by investigating possible contamination sources up-gradient of the identified pollution. In some cases, the watershed boundary may be a limiting criterion. However, pollution in bedrock aquifers is much more difficult to trace. This is because the groundwater contained in the fractured bedrock may not be discernable on the ground and may not, in fact, be related to the surface topography or assumed surface flow direction.
The US Geological Survey (USGS) published the “Geohydrology and Water Quality of Stratified-Drift Aquifers in the Contoocook River Basin, South-Central New Hampshire”; USGS Water-Resources Investigations Report 92-4154; 1995. This report and associated aquifer delineation maps for the Contoocook River Basin were the basis for the Antrim Aquifer Map. The map illustrates the distribution of saturated, unconsolidated, (not bedrock) geologic material on the land surface. There are bedrock aquifers beneath the unconsolidated materials but these were not part of this particular study. The USGS study identifies areas of stratified drift (sand and gravel), provides a measurement of the speed with which water passes through those materials, and estimates the saturated thickness of those materials.
Floodplains are land areas that are susceptible to flooding. These areas actually have two parts: the floodway and floodway fringe. The floodway includes the channel and an additional area that often carries excess flow. The floodway fringe (more commonly known as the 100-year floodplain or the Special Flood Hazard Area) is a broader area over which floodwater may spread, but where the flow velocity is slower. This is an important distinction for land use planning, since some uses can safely occur in the Special Flood Hazard Area, but not in the floodway.
The Federal Emergency Management Agency (FEMA) has mapped the floodplains for all relevant municipalities; the boundaries of the floodplains were computed at cross sections interpolated between cross sections, based on hydraulic information and past experience of flooding.
FEMA maps for Antrim are of two types - a Flood Insurance Rate Map (FIRM), and a Floodway Map. The FIRM defines the 100-year floodplain (meaning there is a 1 out of 100 chance of flooding in any given year; over long periods of time, base floods will occur on the average once every 100 years) and a small area of 500-year floodplain (a 1 out of 500 chance of flooding in any given year). Antrim has a rather large area of floodplain, primarily around the Contoocook and the North Branch Rivers
Antrim’s maps became effective as of April 1, 1981 and the Town was able then to enter into the National Flood Insurance Program, permitting homeowners who live in the floodplain to purchase insurance for their property. However, in order for landowners to be able to purchase this insurance, the town needed to adopt a Floodplain Management Ordinance which was adopted. This Ordinance requires the town to keep track of all development in the Special Flood Hazard Areas and ensure that if any new construction or substantial improvements to a home are proposed for the SFHA, the lowest enclosed floor must be at or above the base flood elevation.
The purposes of this requirement are to minimize the potential for flood damage, to avoid damage-prone uses in the floodplains, and to reduce development pressure of flood hazard areas. Communities that do not maintain and/or enforce their floodplain regulations may be suspended from the insurance program, which could have serious consequences for any affected landowners if their mortgage holders chose to cancel the mortgage. For these reasons, it is very important for the town to keep the floodplain management ordinance up to date by amending it as necessary, and to monitor all development within them.
Trails & Protected Land:
Lily Pond, Ziegler/Hurlin Trail –is a trail system starts at the Meetinghouse Hill cemetery and wends its way down the southern flank of the Meetinghouse Hill. From the trailhead on Route 31, it continues across the highway and out the rear of the old Center cemetery. From the Center Cemetery, the trail travels along a deeded trail easement along the stone wall. The trail formally terminates at the Lily Pond. Land around the pond as well as at the rear of the Meetinghouse Cemetery are privately owned and the land should be treated with the utmost of respect and care. The overall trail length is approximately 4,500 feet, with Route 31 transecting the trail at the halfway point.
McCabe Forest Trail is a trail system cared for by the Society for the Protection of New Hampshire Forests (SPNHF). It is a two-mile trail loop that leaves the parking lot off Route 202 and loops through the 192-acre McCabe Forest to the Contoocook River and back.
DePierrefue-Willard Pond Wildlife Sanctuary (Bald Mountain) Trail System is a sanctuary and trail system maintained by the New Hampshire Audubon Society. The 1,000+-acre sanctuary is the largest New Hampshire Audubon property, and along with additional easements, gifts and protected lands brings the protected lands around Willard Pond to more than 2,000 acres. Willard Pond is about 100 acres is size and is surrounded by Bald Mountain and Goodhue Hill. There are four substantial trails in the system, two of which go to the summits of Bald Mountain and Goodhue Hill.
Loverns Mill Cedar Swamp Preserve is a 613 acre conservation project cooperatively developed and maintained by the Nature Conservancy and SPNHF. The preserve is located along Route 9 in an undeveloped section of North Branch. It contains several trails which transect portions of the property and leads to the nearly 50 acre boreal, cedar swamp. Nature conservation partners have connected the preserve to a larger conservation project. This larger project is to include the 5,000 acre SPNHF owned Peirce Reservation (in Stoddard and Windsor) and the Nature Conservancy’s 1693 acre Otter Brook Preserve.
Meadow Marsh is a short trail (approximately 0.5 miles) on Town property along the wetland areas at the north end of Gregg Lake on either side of Craig Road at the intersection of the former Hattie Brown Road.
Much of Antrim’s landscape is heavily wooded. A large portion of this is located in the Rural and Rural Conservation Zoning Districts of town. These two districts occupy over 70% of Antrim’s land mass. There are hundreds of undeveloped acres in Town under single title ownership. These woodlands are viewed as a renewable resource and are logged on a regular basis. A typical woodlot cut frequency is between 25 and 50 years. What is important for the purposes of this document is the recognition of the potential environmental problems that can occur if care is not taken during woodlot harvesting.
Timber harvesting, if proper erosion control management practices are not utilized, can expose soils to severe erosion. Severe erosion can occur during the construction of skid roads, haul roads, landings, and the cutting of timber on steep slopes. Without proper erosion control mechanisms in place, severe soil erosion may also cause harmful and unlawful sedimentation of wetlands and water bodies, negatively impacting aquatic life by adding nutrient and sediment loads to nearby water bodies.
There are techniques, known as “ Best Management Practices” to control erosion during timber harvesting. The main goal of these practices is to control the water and reduce its effect on the exposed soils. This may be accomplished through the use of proper road ditching, construction of water bars and dips, and proper placement of culverts. Additional erosion control is accomplished through the utilization of silt fences and hay bales, which are placed between exposed soils and water bodies.
Significant Wildlife Areas:
While it could be stated that much of Antrim is a habitat for wildlife, certain areas stand out for the abundance and diversity of wildlife present. A brief listing of wildlife to be found in Antrim include:
Deer, moose, black bear, muskrat, woodchuck, porcupine, beaver, squirrel, chipmunk, mink, fisher, otter, skunk, weasel, raccoon, red fox, coyote, and a wide variety of snakes, frogs, birds, and fishes.
The Rural and Rural Conservation Districts are the districts that have been identified by their nature to be home to these creatures. This is not to say that these wildlife are not found in the other districts, because they are, but that in the two rural districts they can inhabit the ecological niche (habitats) they require.
The more diverse the wildlife species, the greater the need for diverse habitats. Some species require only small areas – less than an acre. Others need hundreds (or even thousands) of acres and some require a mix of different habitat types throughout the year. A diverse habitat is one that consists of a variety of landforms and vegetative cover, for example: open fields, woods, streams, marshes, ridges, and valleys. Significant habitats will typically be connected by migratory routes or wildlife corridors. Frequently, these are found along stream and river paths, ridgelines, large tracts of undeveloped woodlands, etc. The actual documentation of corridors has not been determined for this plan.
A major threat to wildlife is scattered development that results in fragmentation of the habitat. Wildlife might then be “stranded” in an area not large enough to support them. The establishment of the Rural Conservation District in 1989 was believed to help thwart intrusive and fragmented development. This again leads to the importance of sound and prudent zoning regulations established and monitored by the Planning Board.