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Evaluation of rainfall and wetland water area variability at Thirlmere Lakes using Landsat time-series data
Banerjee, B. P.; Raval, S. & Timms, W.
Abstract
Thirlmere Lakes is a group of five freshwater
wetlands in the southwest fringe of Sydney, Australia, that
is subject to cyclic wetting and drying. The lakes are surrounded
by activities that have led to increasing pressure
on the local surface and groundwater supply including
farming and mining. The mine has been operating for more
than 30 years, and in recent times, there has been speculation
that the surface subsidence and underground pumping
may have some impact on surface water and
groundwater hydrology. A study was undertaken using
satellite imagery to examine the relation between water
area changes and rainfall variability. The study utilised
Landsat time-series data during the period 1982–2014 to
calculate changes in the lake water area (LA), through the
normalised difference water index (NDWI) threshold. High
classification accuracy was achieved using NDWI against
high-resolution data that are available for the years 2008
(88.4 %), 2010 (92.8 %), and 2013 (96.9 %). The LA
measurement was correlated against 11 historic observations
that occurred in 2009, 2010, and 2011 during drier
wetland conditions. Correlation analysis of the LA with the
residual rainfall mass spread across the past 30 years has
found that rainfall variability is a major dominant factor
associated with the wetland changes. The underground
mining operations, if verified by independent investigations,
probably play a minor or negligible contributor to
variations in total wetland area during the study period.
This study has demonstrated that remote sensing is a
technique that can be used to augment limited historic data.
Keywords
Wetland monitoring; Remote sensing; Long-term monitoring; Time-series analysis; Landsat
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