Porosity — Science definition

The fraction of a material’s volume that is pore space.

Where it is taught

In use

Porosity is the fraction of a material’s volume occupied by pores.

Groundwater, Watersheds & Water Budgets

Questions using porosity

Problem 1

High porosity always guarantees high permeability.
  1. True
  2. False
Answer and explanation

False

Pores must be well connected and large enough to transmit water readily.

Problem 2

A catchment begins with 300 m³ of stored water. Over one month it receives 100 m³ and loses 70 m³ by outflow/evapotranspiration plus 45 m³ by withdrawal. Find storage change and final storage. Explain why high porosity alone would not guarantee fast recharge.
Answer and explanation

Storage change is 100−70−45 = −15 m³ and final storage is 285 m³. Transmission also depends on connected pathways, permeability, gradients and conditions; porosity alone is a storage fraction.

Combine outputs: 70+45 = 115 m³.

Change is −15 m³; add to initial 300 m³ to get 285 m³.

Distinguish pore-space amount from connected transmission.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 3

Independent chapter check: A catchment begins with 300 m³ of stored water. Over one month it receives 100 m³ and loses 70 m³ by outflow/evapotranspiration plus 45 m³ by withdrawal. Find storage change and final storage. Explain why high porosity alone would not guarantee fast recharge.
Answer and explanation

Storage change is 100−70−45 = −15 m³ and final storage is 285 m³. Transmission also depends on connected pathways, permeability, gradients and conditions; porosity alone is a storage fraction.

Combine outputs: 70+45 = 115 m³.

Change is −15 m³; add to initial 300 m³ to get 285 m³.

Distinguish pore-space amount from connected transmission.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 4

Porosity describes the proportion of a rock that is
  1. solid
  2. pore space
  3. water
  4. mineral
Answer and explanation

pore space

Porosity is the fraction of the volume that is void space.

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