What is Groundwater A number of factors account for the amount of water available in an aquifer, including aquifer thickness, amount of precipitation, topography, surface soil types, porosity, and permeability. Porosity refers to the capacity of earth materials to hold water in spaces found within and between sediments and rock. These open spaces, or pores, allow for the storage and movement of water. If an aquifer contains a mixture of sediment sizes and types, such intermixed clay, sand, and gravel, the smaller sand and clay particles will fill pore spaces, reducing the amount of open space available for storage and movement of water. Thus, well sorted sediments have higher porosity while poorly sorted sediments have low porosity.
Permeability refers to how easily water passes through sediments and rock.
Permeability is a function of the size of pore openings. If sediments are well sorted, pore spaces are uniformly sized, thereby allowing for groundwater flow readily between individual sediment particles. If sediments are poorly sorted, pore spaces are filled with smaller sediments, thereby reducing the movement of water through the deposits. These deposits will supply lower volumes of groundwater.