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

Igneous Rocks
Rocks formed by the solidification of magma. The mineral composition and the grain size of igneous rocks is used as the basis for defining specific rock types.

Impermeable Layer
A layer of a geologic formation (consolidated or non-consolidated) which does not allow water to pass through. Most clays are considered impermeable even although flow may in fact occur at extremely slow rates.

Impervious Area
Impermeable surfaces, such as pavement or rooftops, which prevent the infiltration of water into the soil.

Induced Infiltration (induced recharge)
Pumping from wells adjacent to rivers of lakes that results in river/lake bed flow to the adjacent aquifer.

Infiltration
The downward movement of water into soil and rock formations. Infiltration capacity is exceeded if the volume of rain falling is greater than the rate at which infiltration can take place. Effective infiltration is a term used to describe infiltration which increments ground water. Once in the upper soil layers, further downward movement is sometimes described as percolation. Infiltration can occur as saturated or as non-saturated flow and rates can be very slow in some soil materials. Percolation is usually used to describe saturated flow infiltration. See also percolation.

Injection Well
A well constructed for the purpose of injecting directly into the ground. Usually used to describe wells used for injecting treated (or untreated) wastewater. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into rock formations that don't deliver drinking water, unused aquifers, or below freshwater levels.

Inorganic
Not derived from or made of living matter. Peat is organic. Coal is a rock of organic origin. Rock minerals such a quartz and feldspar are inorganic.

Interception
The trapping and retention of precipitation by vegetation. Small amounts of precipitation may be totally intercepted by plants. Buildings, roads, etc. can also retain precipitation and prevent infiltration occurring. Storm water interception refers to the use of engineering structures to delay the flow effects from storms from reaching rivers and hence reduce the risk of flood damage.

Interflow
Water that infiltrates the soil surface, and then moves laterally through the upper soil layers towards stream channels and other water bodies (lakes and wetlands). Interflow occurs on slopes where lower soil horizons (layers) are less permeable.

Intermittent Stream
A stream or portion of a stream that is dry for a large part of the year and flows only in direct response to precipitation.

Intrusive Rocks
Igneous rocks formed by magma intruding and cooling below the surface. Intrusive rock types include granite and gabbro.

Irrigation
The controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall. There have been many technological changes to increase agricultural irrigation efficiency so that more crop can be produced with less water.

Irrigation Water Use
Water application on to assist in the growing of crops and pastures or to maintain vegetative growth in recreational lands, such as parks and golf courses.