Alluvia in the mid catchment during wetter months

Alluvial aquifers are formed from particles such as gravel, sand, silt and/or clay deposited by physical processes in river channels or on floodplains. Alluvia can contain one or more unconfined, unconsolidated sedimentary aquifers, where groundwater is stored and transmitted through intergranular voids between gravel and sand particles. The recharge of alluvia may occur directly (e.g. through infiltration of rainfall or inundation) or indirectly (e.g. through groundwater connection with surrounding permeable rock aquifers).

During wetter months, unconsolidated sedimentary aquifers in alluvia may provide a range of ecosystems with water required to support their plant and animal communities, ecological processes and delivery of ecosystem services.

• Palustrine (e.g. swamps) and lacustrine (e.g. lakes) wetlands and riverine (e.g. streams and rivers) water bodies on alluvia may depend on the surface expression of groundwater from these unconsolidated sedimentary aquifers.
• Terrestrial vegetation fringing channels on alluvia may depend on the subsurface presence of groundwater in these unconsolidated sedimentary aquifers where groundwater is typically accessed through the capillary zone above the water table.
• Unconsolidated sedimentary aquifers in alluvial deposits may also support ecosystems within the aquifer itself, which sometimes is indicated by the presence of stygofauna.

Pictorial conceptual model PDF

Alluvia in the mid catchment during drier months

Alluvial aquifers are formed from particles such as gravel, sand, silt and/or clay deposited by physical processes in river channels or on floodplains. Alluvia can contain one or more unconfined, unconsolidated sedimentary aquifers, where groundwater is stored and transmitted through intergranular voids between gravel and sand particles. The recharge of alluvia may occur directly (e.g. through infiltration of rainfall or inundation) or indirectly (e.g. through groundwater connection with surrounding permeable rock aquifers).

In drier months the groundwater table may drop below the surface resulting in little or no baseflow. There may be some residual pools trapped by low permeability layers beneath the channel.

Unconsolidated sedimentary aquifers in alluvia may provide a range of ecosystems with water required to support their plant and animal communities, ecological processes and delivery of ecosystem services.

• Palustrine (e.g. swamps) and lacustrine (e.g. lakes) wetlands and riverine (e.g. streams and rivers) water bodies on alluvia may depend on the surface expression of groundwater to maintain or prolong waterholes in the channel which act as critical refugia for plants and animals.
• Terrestrial vegetation fringing channels on alluvia may depend on the subsurface presence of groundwater in these unconsolidated sedimentary aquifers where groundwater is typically accessed through the capillary zone above the water table.
• Unconsolidated sedimentary aquifers in alluvial deposits may also support ecosystems within the aquifer itself, which sometimes is indicated by the presence of stygofauna.

Pictorial conceptual model PDF

Alluvium

Alluvium associated with channels, palaeochannels and topographic depressions may consist of various decomposed materials including, but not limited to, clay, silt, sand, gravel, cobbles, boulders or a combination thereof.

Permeable geology

The alluvium may be surrounded by permeable geological material, such as fractured rock or porous sedimentary sandstone, which contributes to the groundwater contained in the alluvium.

Underlying impermeable geology

Alluvium may be underlain by a confining geological layer which separates groundwater in the alluvium from groundwater contained in a deeper confined aquifer.