Connected Water Resources
A Connected Water Resource is the combination of surface water feature(s), such as a river, estuary or wetland, and the groundwater system(s) that can directly interact in terms of movement of water
Surface water features such as streams are located within a landscape defined by catchment topography, geology and climate. There is a wide array of geological settings so there is variability in the nature and degree of connectivity between surface water and groundwater systems. In its upper reaches, a river can gain groundwater from highly dissected fractured rock aquifers, but lose significant water to its alluvial aquifers further downstream. Towards its lower reaches, seepage may be constrained by deposits of clays and silts. Interaction can vary over time as defined by the difference in stream and groundwater levels, and these can fluctuate with the season.
It is therefore appropriate to perceive a river as not just the river channel and associated surface water features (such as wetlands and lakes) but also the aquifers within which the river is located. Surface water and groundwater systems are highly connected if the movement of water between these systems has implications for water quantity and/or quality over a specified planning timeframe. Groundwater-surface water interactions need to be assessed and managed for highly connected water resources to protect dependent economic, social, and environmental values. Examples of highly connected water resources include the combination of:
- high baseflow unregulated streams and surrounding aquifer where groundwater seepage defines low flow stream conditions;
- shallow alluvial aquifer and stream where groundwater recharge is reliant on leakage from the overlying stream;
- rivers and surrounding aquifer where seepage of saline groundwater contributes significantly to in-stream salinity; and
- lakes (or wetlands) and underlying aquifer where input of nutrient-rich groundwater can initiate algal blooms.
Surface water and groundwater systems are weakly connected if movement of water between these systems is limited and has no significant impact on water quantity and/or quality over a specified planning timeframe. Examples of weakly connected water resources include:
- where stream and aquifer is separated by impermeable layers (such as clay) that impede the movement of water; and
- where the hydraulic gradient between stream and aquifer is low.
Weakly connected water resources still need to be assessed and monitored in terms of changes in hydraulic conditions. For example, watertable mounding due to land use change (such as irrigation development) can alter hydraulic gradients and induce groundwater discharge to the stream. Also weakly connected water resources can be used to advantage. For example, the aquifer component could be used in water banking without significant losses from storage due to leakage to surface water features.