Geology & Groundwater Hydrology Flashcards

What does the specific yield of an unconfined aquifer represent?

Answer: The volume of water released per unit drop in hydraulic head per unit area

Specific yield is the volume of water that drains by gravity from a unit volume of aquifer material per unit decline in the water table.

A perched water table occurs when:

Answer: Groundwater accumulates above a localized impermeable layer above the regional water table

A perched aquifer forms when a lens of low-permeability material intercepts downward-percolating water, creating a localized saturated zone above the main water table.

Which geologic process is responsible for creating the primary porosity in sandstone aquifers?

Answer: Depositional pore spaces between grains

Primary porosity in sandstone results from the spaces between sand grains that were preserved during original sediment deposition and cementation.

The vadose zone is best defined as:

Answer: The unsaturated zone between the land surface and the water table

The vadose zone (unsaturated zone) extends from the land surface to the water table and contains both air and water in pore spaces.

What is transmissivity in hydrogeology?

Answer: The product of hydraulic conductivity and saturated aquifer thickness

Transmissivity (T = K × b) describes the ability of an aquifer to transmit water horizontally and depends on both the material's conductivity and the saturated thickness.

Stream gauging data shows baseflow increases after no recent rainfall. This MOST likely indicates:

Answer: Groundwater is discharging into the stream (gaining stream)

A gaining stream receives groundwater discharge from adjacent aquifers, which can sustain or increase streamflow during dry periods.

Which grain size class generally has the highest hydraulic conductivity?

Answer: Coarse gravel

Coarse gravel has large, well-connected pore spaces that offer minimal resistance to flow, resulting in the highest hydraulic conductivity of common sediment types.