Geophysical Methods and Groundwater

Vocabulary flashcards covering key concepts, equations, geophysical techniques, and construction dewatering methods from the Geophysical and Groundwater lecture notes.

Groundwater

Water held in the spaces between soil, sediment, and rock below the surface of the Earth.

Aquifer

A groundwater-bearing geological formation that can store and transmit usable quantities of water.

Groundwater Recharge

The process by which rainwater or surface water seeps into the ground and moves downward to replenish underground aquifers.

Groundwater Cycle

The transfer of water from the atmosphere to underground formations and back to the surface via discharge into springs, rivers, lakes, wetlands, or wells.

Aquitard

A geologic formation with low permeability that restricts or prevents the flow of groundwater between aquifers.

Unconfined Aquifer

An aquifer whose upper boundary is the water table and is not restricted by an overlying impermeable layer, allowing direct recharge from surface infiltration.

Confined Aquifer

An aquifer bounded by aquitards or impermeable rock layers, holding groundwater under pressure higher than atmospheric pressure.

Water Table

The surface marking the top of the saturated zone in an unconfined aquifer, serving as the boundary between unsaturated and saturated ground.

Porosity

The proportion of total volume occupied by pore space inside soil or rock where water can be stored, expressed as $n = \frac{V_v}{V_t}$.

Permeability

The capacity of a soil or rock material to allow water to pass through its interconnected pore network.

Hydraulic Conductivity

A measure ($K$) of how easily a porous medium transmits groundwater under a given hydraulic gradient, depending on pore geometry and fluid properties.

Storativity (Storage Coefficient)

The volume of water released from or taken into storage per unit surface area of an aquifer per unit change in hydraulic head.

Specific Yield

The ratio of the volume of water that a saturated soil or rock will yield by gravity to its total volume, calculated as $S_y = n - S_r$.

Groundwater Flow

The underground movement of water through pore spaces and fractures, driven from areas of higher hydraulic head toward areas of lower hydraulic head.

Hydraulic Gradient

The rate of change in hydraulic head per unit distance in a given direction, defined as $i = \frac{\Delta h}{\Delta L}$.

Seepage

The slow movement of fluid passing through the small pores or openings of a porous soil or rock mass.

Darcy's Law

A fundamental equation governing flow in porous media, stating that flow rate is proportional to hydraulic conductivity and hydraulic gradient, given by $q = -K i$ or $Q = K i A$.

Electrical Method

A geophysical technique that measures subsurface electrical resistivity to detect water-saturated zones, clay layers, and aquifer structures.

Seismic Method

A subsurface exploration method that uses seismic wave velocity and reflection/refraction patterns to identify bedrock depth and fractured zones.

Magnetic Method

A geophysical method measuring localized variations in Earth's magnetic field to locate faults, fractures, and geological boundaries that influence groundwater flow.

Gravity Method

A survey technique measuring subtle variations in Earth's gravitational acceleration to detect density differences, sedimentary basins, and buried valleys.

Electromagnetic Method

A rapid geophysical method utilizing electromagnetic fields to map soil conductivity, locate saline water zones, and map buried clay beds.

Ground-Penetrating Radar (GPR)

A high-frequency electromagnetic wave imaging technique used to locate shallow water tables, soil layers, bedrock interfaces, and shallow buried utilities.

Test Well

An exploratory borehole drilled to verify groundwater presence, aquifer thickness, yield capacity, and water quality prior to full-scale development.

Observation Well

A monitoring well constructed to measure water-table fluctuations, recharge response, and drawdown effects during nearby extraction.

Pumping Test

A field test involving water extraction at a controlled rate while recording water level drawdown to calculate aquifer properties like transmissivity and hydraulic conductivity.

Hydrostatic Pressure

The upward and lateral force exerted by standing groundwater against subterranean structural foundations and basement walls.

Sump Pump

A mechanical dewatering system consisting of a pit with a top grate and a submersible pump used to collect surface water and discharge it to higher ground.

Wellpoints

A series of closely spaced, small-diameter shallow wells connected to a surface vacuum pump, designed for groundwater drawdown up to $5\text{ to }6\,m$ depth.

Drainage System

An assembly of plastic or metal piping installed to collect, divert, and remove stormwater, wastewater, or excess groundwater away from structural works.