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Glossary of Water-Related Terms

Introduction

In order to fully appreciate the value of our water resources and to begin to consider stratagies for managing them appropriately, it is important to know what the various components of natural water systems are, what roles they play, and why they are important. Many important terms are too-loosely defined or commonly misunderstood. This glossary is not an exhaustive dictionary of hydrological terms but is meant to familiarize the layperson with some of the concepts most important to effective watershed management. (For an extremely thorough dictionary of water related terms see Nevada Division of Water Planning's Water Words Dictionary from which some of these definitions were taken.) Each term has a brief definition followed by a description of that item's function and significance.


Aquifer - a geologic formation that stores water beneath the earth's surface

An aquifer is not a void beneath the earth's surface filled with water but is a zone of comparatively porous material such as chalk, sandstone, or gravel confined by less porous material. Water flows into the aquifer filling the voids in the aquifer material. When an aquifer is not closed at the top it is known as an unconfined aquifer, and the upper surface of it is the water table. Wells and springs draw water from aquifers and many areas rely completely on aquifer water for thier private, municipal, industrial, and agricultural water needs. Aquifers are subject to contamination and depletion. Overdrawn or depleted aquifers are serious concerns in areas highly dependent on aquifer water.


Aquifer Recharge Area - an area in which water can infiltrate the soil and replenish an aquifer relatively easily

Aquifer recharge areas allow precipitation to reach an aquifer by infiltration. Recharge areas are often much smaller than the total aquifer area and are therefore very important to the aquifer. Artifically increasing runoff in a recharge area through paving or clearing can devastate an aquifer.


Groundwater - water that infiltrates the earth's surface

Groundwater originates as precipitation and is suspended by the soil for varying lengths of time depending on soil type, vegetation cover, and land use. Groundwater is reponsible for feeding vegetation and for recharging aquifers.


Hydrologic Cycle (Water Cycle) - the circuit of water movement from the earth's atmosphere to the earth and back through sequential stages such as precipitation, runoff, infiltration, evaporation, transpiration, etc.

The hydrologic cycle has many different variations. Typically, water vapor in the atmosphere falls to the earth as rain. It is then transported to an open body of water via streams and rivers or through runoff or aquifer discharge. It is then evaporated and returns to the atmosphere as vapor. Alternately, once water enters the soil it may be absorbed by plants and returned to the atmosphere through transpiration (evapoation of water from the leaves of a living plant). Basic Ground Water Hydrology has illustrations and a more in-depth discussion of the hydrologic cycle.


Hydrology - the science of earth's water resources

The scope of hydrology includes water's occurence, distribution, circulation, physical and chemical properties, and reactions with and effects on the environment.


Leachate - liquid which percolates through the ground, such as water seeping through a landfill

Leachate refers to the contaminated water that runs off of and out of sanitary landfills. It has the potential to contaminate rivers, lakes, etc.


Non-Point Source Pollution (NPS) - pollution discharged over a wide land area rather than from a specific location

Non-point source pollution actually originates from numerous small sources. It is quickly spread out and diffused, and it generally infiltrates the soil contaminating the groundwater or is deposited by runoff into rivers and lakes. NPS is much more difficult to measure and control than pollution from a specific point such as a sewer drain or a smoke stack. Agricultural chemicals and exhaust deposits in streets are examples of non-point source pollution. (See the Nonpoint Source Pollution Control Program for more.)


Runoff - rainwater that does not infiltrate the soil but flows across the earth's surface into a body of water

The proportion of rainwater that penetrates the soil varies considerably depending on soil type and area covered by impervious materials. Runoff has the potential to "carry" contaminants resting on the earth's surface into streams, lakes, reservoirs, etc. A watershed with a high percentage of its area covered by impervious materials (pavement and buildings) will have a comparatively high rate of runoff. Runoff is especially problematic in agricultural areas where residues from agricultural chemicals and high concentrations of animal waste rest on the earth's surface.


Water Resources - the supply of groundwater and surface water in a given area

Water resources is a general term used to describe all of the usable water in a specific geographical area.


Watershed - a region or area over which water flows into a particular, lake, reservoir, stream, or river; a drainage basin

U.S. watersheds are deliniated by the USGS. There are 21 regions in the lower 48 states encompassing a total of 2,149 watersheds (refered to by USGS as cataloguing units; see Surf Your Watershed). Watersheds are separated by ridges or areas of high ground. The boundary between two watersheds is a line connecting points of runoff divergence. Generally, a river or stream runs through a watershed collecting runoff. The stream then flows into another watershed downstream or into the sea.


Watershed Management - the process of analyzing and maintaining the land and water resources of a watershed in order to conserve those resources for the benefit of the watershed's residents

Since watersheds are defined by natural hydrology, watershed management is the most logical water conservation approach. Many problems are better solved at the watershed level than by addressing individual problems within a watershed. Effectively managing a watershed requires knowledge of it attainable only through thorough research. The watershed's natural resource base, health status, threats, and land use patterns as well as the needs of its residents must be understood. Good watershed management takes advantage of community resources and involves cooperation of various community organizations and residents.


Water Table - the level of groundwater saturation

The depth of the water table is determined by the quantity of groundwater and the permeability of the earth material and fluctuates accordingly. The water table is often the upper surface of an unconfined aquifer.


Wetland - an area where water saturation is the dominating factor determining the nature of soil development and the types of plant and animal communities living in the surrounding environment

Wetlands include swamps, marshes, bogs, ponds, sloughs, esuaries, bottomland hardwoods, fens, mangrove swamps, pocosins, vernal pools, prairie potholes, and more. Numerous government agencies have unique definitions of wetlands that suit their own regulatory responsibilities. The one feature common to all definitions is soil saturated with water during at least part of the growing season. Most definitions also include one or more of the following conditions:
The ecological importance of wetlands would be difficult to overstate. They support wildlife that cannot exist otherwise, purify polluted water, and mitigate the destructive power of floods and storms. Wetlands provide breeding grounds and habitat for countless animal species many of which are rare or endangered. At least one-third of the nation's endangered species live in wetlands. Many wetlands are rich sources of timber, and others are relied upon for fish and shellfish production. Coastal wetlands absorb storm energy and slow currents thereby protecting shorelines. Water stored in or slowed by a wetland can more easily be absorbed as groundwater. Wetlands and wetland vegetation filter and retain sediments and toxicants protecting the quality of downstream waters. Additionally, wetlands offer an array of unique recreational opportunities.

An estimated 54 percent of wetland area in the United States has vanished since colonial times. In recent decades studies have demonstrated the ecological importance of wetlands and wetland management. Various federal and state regulations now govern land use in wetlands requiring minimum-impact development and wetland replacement practices.


Sources

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