Glossary of terms

Anadromous fish: fishes that live in marine waters and migrate to freshwaters to spawn. Local examples: alewife and American shad.

Aquifer: a geologic formation that is capable of yielding a significant amount of water to a well or spring.

Areas of contribution: the upland recharge areas and cone of depression from which well water is drawn.

Area of influence: the two-dimensional area (as viewed on a map) of water table drawdown created by a pumping well. See cone of depression.

Artesian aquifers: see confined aquifer

Baseflow: the discharge of groundwater from the zone of saturation to surface water bodies, such as lakes and streams.

Basin: drainage basin. See watershed.

Benthic: associated with the substrait or bottom of a body of water.

Catadromous fish: fishes that live in freshwaer and migrate to salt water to spawn. Local example: American eel.

Cone of depression: the three-dimensional area of water table drawdown created by a pumping well. A pumping well creates an artificial discharge area by drawing down (lowering) the water table around the well.

Confined (or Artesian) aquifers: aquifers found between layers of clay, solid rock, or other materials of very low permeability. Water in confined aquifers is often under pressure because the aquifer is confined between impermeable layers and is usually recharged at a higher elevation than the top confining layer.

Endemic: native and restricted to an area.

Eutrophication: accumulation of nutrients in lakes and other bodies of water that causes rapid growth of vegetation; usually resulting from human activity.

Exotic: not native, introduced to an area by humans.

Extirpated: refers to a species or subspecies lost from parts of its total range.

Glacial till: the unsorted deposits of glacial debris pushed to piles by the last advance of the glaciers. They consist of an unsorted mixture of all sizes of soil and rock fragments and are usually not very porous or permeable - i.e. not good aquifers.

Permeability: ability of a material to transmit water. Permeability determines its ability to yield water.

Groundwater: the water beneath the surface of the ground.

Groundwater recharge: the filling of groundwater aquifers by rain and melting snow percolating into the ground and saturating the pores between rock and soil particles.

Induced recharge: the phenomenon of drawing water from a stream into a well. Induced recharge occurs when the cone of depression reaches as far as the stream, thereby lowering the water table beneath it and thereby reversing the direction of groundwater flow.

New England Aquatic Base Flow (ABF) method: a method developed by the US Fish and Wildlife Service for calculating summertime streamflow recommendations based on median monthly mean flows for August. The "default" ABF recommendation for summertime flows is 0.5 cubic feet per second per square mile of drainage area.

Porosity: the ratio of the volume of pore space to the volume of solids in a material. Porosity determines the capacity of the material to hold water --the more pores, the more water.

R2Cross: the method developed in Colorado (Nehring, 1979) for measuring minimum streamflow needed to protect aquatic habitats in streams. The method is based on the assumption that flow sufficient to maintain habitat in a riffle will also maintain fish habitat in nearby pools and runs. The method is being adapted by USGS for use in New England.

Recharge areas: the places where rain and snow melt percolate into the ground, refilling the groundwater aquifers.

Stratified drift: the size-sorted deposits of glacial debris created by the torrents of water that flowed off the retreating glaciers in meltwater streams. Many stratified drift deposits were eroded and redeposited multiple times by flowing water. This repeated sorting action created porous, permeable, stratified drift deposits that often make excellent aquifers.

Subbasin: see subwatershed.

Subwatershed: the land area draining runoff to a tributary of a larger river.

Surficial deposits: the sand, gravel, soils, rocks, and other loose material that lie on top of bedrock.

Tennant method: the method developed by D. L. Tennant for calculating seasonal in-stream flow needs for fish. Published in 1976, the method is based on seasonal percentages of the mean annual flow of a stream.

Total length (of fish): a method of measuring fishes often used by anglers and fisheries biologists. The maximum length of the fish from furthest projections of jaw or snout to tip of the tail.

Unconfined (or water table) aquifer: an aquifer where top of the aquifer is identified by the water table. Above the water table, known as the zone of aeration, interconnected pore spaces are open to the atmosphere. Also known as a water table aquifer.

Water table: the top of the saturated zone underground.

Water table aquifer: see unconfined aquifer

Watershed: The land area that drains runoff to the stream, or other surface water body. Also called a drainage basin. For management purposes, the Massachusetts Department of Environmental Protection recognized 27 major watersheds in Massachusetts.

Zone of aeration: the underground area, above the zone of saturation, where both air and moisture are found in the spaces between soil and rock particles

Zone of saturation: the area underground where every pore space between rock and soil particles is saturated with water.