Groundwater, Hydrogeology, and Geohazards

Porosity

The capacity of a subsurface porous medium to store fluids, measured as a ratio of void space to total volume.

Permeability

A hydraulic property that describes how fast water can move through a subsurface material.

Recharge

The process of adding water to the groundwater system.

Discharge

The removal of water from the groundwater system through springs, wells, or seepage.

Confined Aquifer

An aquifer that is trapped between impermeable layers.

Unconfined Aquifer

An aquifer that is open to surface recharge.

Aquifer

A geological formation that can store and transmit water.

Aquitard

A layer of material with low permeability that restricts water flow, such as clay.

Artesian Well

A well where water flows freely to the surface due to the potentiometric surface being above ground level.

Land Subsidence

The sinking of the ground surface due to excessive groundwater extraction.

Mudpot

A geothermal feature where groundwater upwells through volcanic or ash-heavy soils.

Water Table

The boundary between the saturated and unsaturated zones in the subsurface.

Primary Porosity

Porosity that occurs during the formation of rock.

Secondary Porosity

Porosity that develops from fractures or dissolution after the rock has formed.

Dendritic Drainage Pattern

A tree-like drainage pattern formed by rivers and streams.

Mass Movement

The downslope movement of soil and rock due to gravity.

Slump

A type of landslide where material moves along a curved surface, creating a rotational movement.

Ephemeral Stream

A stream that flows only during and shortly after rain.

Perennial Stream

A stream that flows continuously throughout the year.

Meandering Stream

A stream with a sinuous, looping channel.

Stream Gradient

The slope of a stream channel.

Saltation

The bouncing movement of sediment particles along the stream bed.

Floodplain

Low-lying areas adjacent to rivers that are subject to flooding.

Levee

An embankment built to prevent the overflow of a river.