Groundwater discharge into river/stream

Satellite(s) Landsat-7 TIR.	Monitoring element River water temperature.

Satellite(s)

Landsat-7 TIR.

Monitoring element

River water temperature.

Description technique

Lalot et al. (2015) utilised a series of images to establish longitudinal temperature profiles of a river where it flows above an aquifer.
The groundwater discharge along the river course was quantified for each identified groundwater catchment area. A heat budget was based on river temperature variations estimated from the Thermal Infra Red (TIR) images.

Accuracy / Resolution

75% of the temperature differences, between in situ observations and TIR image-based estimations, remained within the ±1 ◦C interval.

Case study

Investigation over a 135km reach of the Loire River (France).
Width of the wet section: 200-450m.
Average flow rate 345m³/s in Orléans
(1964-2011 period).

Benefits

The advantage of Landsat satellite images over airborne images is that they are freely available at different dates, providing archives to explore inter-annual or seasonal patterns. As the surface area covered by a single satellite image would require a long time to be covered by air, longitudinal thermal profiles derived from TIR satellite images also show less bias due to change in water temperature during sampling time.

Limitations

Only large river courses can be studied using TIR satellite images, as it is usually considered that river width must exceed 3 image pixels to provide an accurate estimation of water temperature (e.g., 1 pixel of Landsat-7 of the TIR image represents 60mx60m on the ground).
River temperature can be seriously underestimated at low flow rates and high water temperatures (differences of over 2 ◦C).

Applicability for Northland

Yes, potentially.

A finer spatial scale thermal infra-red imagery (e.g., imagery acquired by UAV) would probably be required to fit Northland's river widths.

Publication references

Lalot E, Curie F, Wawrzyniak V, Baratelli F, Schomburgk S, Flipo N, Piegay H, Moatar F. 2015. Quantification of the contribution of the Beauce groundwater aquifer to the discharge of the Loire River using thermal infrared satellite imaging. Hydrol Earth Syst Sci. 19(11):4479-4492. doi:10.5194/hess-19-4479-2015.

https://hess.copernicus.org/articles/19/4479/2015/

Other comments or information

Locating groundwater discharge areas is crucial to assess the vulnerability of aquatic fauna, as these locations can act as sheltered areas.

Other references

Huang Z, Tang Q, Lo M-H, Liu X, Lu H, Zhang X, Leng G. 2019. The influence of groundwater representation on hydrological simulation and its assessment using satellite-based water storage variation. Hydrological Processes. 33(8):1218-1230. doi:10.1002/hyp.13393.

https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.13393