A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Habitat
The environment in which the life needs of organisms/ plants/ animal populations is supplied.

Hardness
A water quality index that describes the concentration of alkaline salts in water, mainly calcium and magnesium. If water is "hard" then more soap, detergent or shampoo is necessary to make bubbles for effective washing/ cleaning. Hardness is measured in milligrams per liter (mg/l) but may also be reported in the archaic form of grains per gallon. [One grain of hardness equals 17.1mgl] Typical water hardness classifications are:

Soft water	less than 17mg/l
Slightly hard	17 - 60 mg/l
Moderately hard	60-120 mg/l
Hard	120-180 mg/l
Very hard	180 + mg/l

Headwater(s)
A descriptive rather than a scientific word. Generally it describes the upper parts of a watershed that contribute flow to a specific river or storage reservoir.

Heavy Metals
Metallic elements with high atomic weights (e.g., mercury, chromium, cadmium, arsenic, and lead). They can damage living organisms at low concentrations and tend to accumulate in the food chain. Fish are particularly susceptible to mercury.

Hydraulic Conductivity
The rate of flow of water through a unit cross section of aquifer (ft squared or m squared) under a unit hydraulic gradient. Expressed as g.p.d./ft squared or m/day. The hydraulic conductivity of an aquifer is an important parameter used in ground water management calculations.

Hydraulic Conductivity
A property of an aquifer (or part of an aquifer) that is measure of the ability of the rocks/ sediments to allow water to flow under specific hydraulic gradients.

Hydraulic Gradient
A measurement used in ground water science to calculate directions and rates of ground water flow. The hydraulic gradient is the slope of the water table in unconfined aquifers or the pressure surface in confined aquifers. It may be measured from the point of recharge to the point of discharge or between any two places within a ground water system. The hydraulic gradient is a ratio of the vertical difference between two places on the water table and their horizontal distance apart.

Hydric soil
Soil that is saturated or flooded long enough during the growing season to develop anaerobic conditions in its upper layers.

Hydrobabble
Description of mistaken concepts in hydrology usually expressed as "facts" by people who do not have the scientific background to understand cause-and effect in the hydrologic system.

Hydrofracture
A technique of increasing flow to a well in bedrock by using high-pressure forces down a well to open fractures. The technique is typically used to increase flow in very low yielding wells.

Hydrogeology
The study of geology from the perspective of its role and influence in hydrology. On the other hand, geohydrology is a term used to describe the study of hydrology from the perspective of the influences of geology. In practice both terms are used interchangeably. Ground water science is the common field of study.

Hydrograph
A graphical plot of discharge vs. time for stream flow. Well hydrographs show changes of ground water levels vs. time.

Hydrologic Budget
An accounting concept used for a specific time interval (usually a year) to quantify the inputs, outputs and changes in storage of water within a geographically defined hydrological system.

Hydrologic Cycle
A description of the circulation of water on Earth involving transfers and storage of water vapor from the Earth's surface via evapotranspiration into the atmosphere, from the atmosphere via precipitation back to earth, and through infiltration to ground water, runoff into streams, rivers, and lakes, and ultimately into the oceans.. The sun is the energy source that raises water from the oceans and land into the atmosphere. The force of gravity influences the surface and subsurface movement of water on land. Hydrologic system is a more accurate description.

Hydrologic System
A more accurate way of describing the many processes involved in the hydrologic cycle.

Hydrology
The scientific study of the properties, circulation and distribution of water as it occurs within the atmosphere and at and below the earth's surface. Hydrology is a very broad term encompassing many sub-disciplines. It generally does not include oceanic/marine sciences or meteorological sciences but does include the hydrologic aspects of ground water, rivers and wetlands.

Hydroperiod
The duration of a particular flooding event. The period during which surface water remains on a wetland. This may range from a few days to several months or may be seasonal or permanent.

Hydrophytes
Plants adapted to life in water, or in periodically flooded and/or saturated anaerobic soils. Plant characteristics include air filled root tissues, floating leaves and buttressed tree roots.