Framework

Field Observations

The interaction of groundwater and surface water systems can be directly observed in certain catchments and settings. A field reconnaissance survey can be useful in the initial stages of an assessment to identify specific locations (hotspots) that warrant further investigation involving more detailed monitoring and sampling. The survey can also provide guidance to the parameters that could be measured to help quantify connectivity and also to identify the management issues impacted by the connectivity.

There are a range of field indicators of direct groundwater discharge into streams, lakes or estuaries including:

  1. the direct observation of water flow from seepages and springs at the margins or within the bed of the surface water feature. Underwater discharge of groundwater can be observed if the flow rates are sufficiently high;
  2. in colder times of the year, the water vapour above discharge zones may be observed due to the contrast between the groundwater and air temperatures. Likewise, in alpine areas during winter, seepage areas can remain continually ice or snow-free in contrast with their surroundings;
  3. changes in the groundwater chemistry due to mixing with surface water can result in mineral precipitates such as iron and manganese oxides. These commonly form with the contact of anoxic groundwater with oxygenated surface water. Iron bacteria that oxidise the dissolved ferrous form (Fe2+) to the ferric form (Fe3+) can also occur as filaments and accumulations. This can be accompanied by an oily sheen on the water surface, similar in appearance to a petrol film. A bacterial origin (rather than a petrol spill) is inferred if the film breaks up into clusters rather than swirling together, when a small stick is trailed through it (NCDWQ, 2004);
  4. carbonate precipitates such as tufa or travertine deposits can indicate discharge of groundwater with high levels of dissolved carbon dioxide and calcium carbonate, notably in a karst landscape. These can form spectacular terraces, cascades and dams that can significantly modify stream morphology. Precipitation commences downstream of where groundwater discharge occurs, when degassing of carbon dioxide leads to supersaturated conditions in the surface water with respect to calcite. Stream reaches with abrupt changes in gradient tend to be preferred sites of deposition because turbulent stream flow can enhance carbon dioxide outgassing. Biological factors, such as algae or bacteria growth, can also influence carbonate precipitation; and
  5. water colour and odour can be an indicator, particularly if the groundwater is contaminated. This may be the case in catchments with urban, industrial, mining or intensive agricultural development. Discharge of highly acidic groundwater can be indicated by a dramatic increase in the clarity of the surface water, due to the flocculating of clay particles by elevated levels of dissolved aluminium.

Advantages

  1. readily incorporated into field work program with no additional costs;
  2. useful as a reconnaissance tool to target investigation sites and guiding subsequent sampling and analysis.

Disadvantages

  1. dependent on observer's knowledge of indicators of groundwater-surface water interaction in the field;
  2. tends to show where groundwater seepage occurs but is limited in providing quantitative information on seepage flux.

Data Availability

Databases specific to field observations are not routinely maintained. However, field observations relating to the collection of water samples may be relevant, refer Water Quality Data

Case Studies

Tuckean Swamp
Barkly karst

References

NCDWQ, 2004. Stream Identification Method Version 3 (Draft). North Carolina Division of Water Quality.