Oral Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Locating groundwater discharge into a large coastal lagoon (498)

Katie Coluccio 1 , Leanne K. Morgan 1 2 , Luke Jeffrey 3 , Marwan Katurji 4
  1. Waterways Centre for Freshwater Management, University of Canterbury, Christchurch, New Zealand
  2. School of the Environment, Flinders University, Bedford Park, SA, Australia
  3. Southern Cross GeoScience, Southern Cross University, Lismore, NSW, Australia
  4. Centre for Atmospheric Research, University of Canterbury, Christchurch, Canterbury, New Zealand

Objectives
The objective of this study was to identify the spatial distribution of groundwater seepage into Te Waihora/Lake Ellesmere, a large (200 km2), shallow coastal lagoon in Canterbury, New Zealand. This lagoon holds important ecological, cultural and recreational values, yet has suffered from significant water quality decline in recent decades.

Design and methodology
This study used broad-scale methods to identify the spatial distribution of groundwater inflow into the lagoon during the summer. An airborne thermal infrared imaging survey was flown over the lagoon to detect relative cool patches indicating possible groundwater inflow. This dataset was compared with physical and chemical parameters (radon-222, conductivity, temperature, dissolved oxygen) measured in the lagoon by boat.

Original data and results
Data analysis revealed areas of groundwater seepage into Te Waihora at locations previously identified, as well as areas not known before this study. The data identified both point-source springs and diffuse seepage. This study conducted the first broad-scale survey of seepage into the lagoon and found groundwater inflow in locations previously thought to be unlikely. This dataset will allow for follow-up work to improve the estimate of the groundwater proportion of the lagoon’s water budget in light of identifying these new seepage locations.

Conclusions
This study demonstrates the successful use of broad-scale methods for identifying the spatial distribution of groundwater discharge into a large coastal waterbody.