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Wetlands are areas with soils that drain slowly, creating soil conditions that usually have water near the surface for at least part of the year and resulting low oxygen levels. These wetland, or “hydric”, soils support plants adapted to such conditions. Wetlands are usually transitional areas between drier upland soils and deep water areas such as streams, rivers, ponds and lakes.  Wetlands include forested and shrub swamps, marshes, wet meadows and peatlands.  Wetlands provide many valuable benefits such as wildlife habitat, storing floodwaters and reducing flood damage, improving water quality and providing recreational opportunities. Having knowledge about local wetlands enables communities to proactively plan to conserve this critical resource.

Wetland functions can play a role in climate adaptation. They buffer the impacts of more intense storms, minimizing flooding, erosion and property damage. Flood storage is a key function of wetlands. Storage of precipitation and runoff in wetland areas high in a watershed can help to minimize downstream flooding, while wetland areas lower in the watershed can store and gradually release larger volumes of runoff, reducing flood peaks. Wetlands can reduce the quantity of pollutants and sediment from runoff associated with more intense storm events. In times of drought, wetlands provide storage of water and potential recharge of ground water. As wildlife habitat, wetlands may facilitate a shift in range in response to warming climate or related impacts. Along New Hampshire’s coast, protecting upland areas behind existing salt marshes provides areas for salt marshes to migrate as sea levels rise.

Basic NRI - What to Include:

All that is needed for the Basic NRI is an inventory of wetlands in the study area (see Sample Map). Several data sources are available that provide a good starting point for inventorying local wetlands. The primary resource for wetlands data is the NH Wetlands Mapper. Wetlands data can also be found on the GRANITView mapper and GRANIT. There are several data sources for wetlands: 
NRCS County Soil Survey data provide information about "hydric soils" - poorly drained soils and very poorly drained soils
characterize wetland areas. Hydric soils are soils that formed under conditions of saturation, flooding or ponding long enough during the growing season to develop oxygen-deficient conditions in the upper layers. Poorly drained soils may be saturated periodically during the growing season or remain wet for extended periods and very poorly drained soils remain wet during most of the growing season since the water table is at or above the surface most of the year. In general, the soils maps tend to overestimate the acreage of wetland soils due in part to the scale of soil mapping.
National Wetlands Inventory (NWI) is a program administered by the US Fish and Wildlife Service for mapping and classifying wetland resources in the United States. The NWI maps show the distribution of wetlands on the landscape and classifies wetlands by vegetation classes, wetland hydrology and other factors.
In general, the NWI maps tend to underestimate wetland acreage (e.g. some forested wetlands are hard to detect from satellite imagery). Typically, NWI maps and hydric soils data are used in combination for the initial wetlands inventory. However, the sources of information for NWI maps and NRCS Soil Surveys may be dated, e.g. NWI maps were originally compiled using 1984 infrared aerial photography.  NWI data has been updated for coastal NH (2014) and some other parts of the state where specific studies have been conducted.
NH Wetlands Base Map: In 2010, the NH DES Watershed Management Bureau and Wetlands Bureau developed a wetland base map for the state using NWI data. This is intended to provide the first step in wetland mapping. The NH Wetlands Base Map can be accessed via the NH Wetlands Mapper or GRANIT. The map uses the current NH Method Guidelines for Determining Wetland Evaluation Units to indicate where potential wetland breaks may exist. 

Detailed Inventory Studies:

Wetland functions represent the practical, measurable values of wetlands, such as wildlife habitat, sediment trapping, flood storage, etc.  For many communities, wetland evaluation and prioritization are an important feature of their NRI.
Wetland Evaluation is the process of determining the values of a wetland based on an assessment of the functions that it performs. Using the inventory of wetlands from the Basic Inventory, wetlands can be selected for detailed evaluation. This involves a good amount of field work to collect data. The Method for Inventorying and Evaluating Freshwater Wetlands in New Hampshire (NH Method) was developed for communities and professionals to have available a practical means of inventorying and evaluating their wetlands. The NH Method provides a consistent basis for evaluating wetlands across the state.
Prime Wetland Designation – New Hampshire law has a provision that allows a municipality to designate certain wetlands within its borders as being worthy of extra protection because of their size, uniqueness, fragility,
unspoiled character or other relevant factors that make them of substantial significance.  Reference pages 1 and 2 in Appendix A of the NH Method for more information about Prime Wetlands and NH Wetlands Rules. Prime wetlands can be evaluated using the NH Method.
Wetland Buffers are the naturally vegetated upland areas adjacent to a wetland that are important for both water quality and wildlife habitat.  See the Shorelands section for more information about buffers for wetlands and surface waters.  If a goal is to protect buffers around significant wetlands refer to the Buffers on the Bay website. Note that this information is focused on the coast, much of the information is relevant for inland buffers as well.
Vernal Pools are wetlands with a seasonal cycle of flooding and drying
that can be documented using other tools (the NH Method is not suited to evaluating vernal pools). Refer to Vernal Pools in the Wildlife Habitat section of the NRI Guide for more information on documenting these wetlands.

Additional Resources:

Method for Inventorying and Evaluating Freshwater Wetlands in New Hampshire (NH Method)
NH Department of Environmental Services Wetlands Bureau
for information about wetland regulations, prime wetlands, wetlands grants and more
New Hampshire Water Resources Primer
provides information about the state’s water resources (including wetlands) and the challenges faced in sustainably managing them
Google Earth
for close up imagery of wetlands
NH Wetlands Mapper for wetlands data
NH Coastal Viewer includes information about floodplains, salt marsh migration and sea level rise predictions/scenarios for communities in New Hampshire's coastal watershed.