A water coverage extraction approach to track inundation in the Saskatchewan River Delta, Canada

Tracking surface water coverage changes is a complicated task for many regions of the world. It is, however, essential to monitor the associated biological changes and bioproductivity. We present a methodology to track contemporary water coverage changes using optical remote sensing and use it to estimate historical summer water coverage in a large river delta. We used a geographical information system automated routine, based on the modified normalized difference water index, to extract the surface water coverage area (SWCA) from optical satellite data sets using the surface water extraction coverage area tool (SWECAT). It was applied to measure SWCA during drought and flood peaks in the Saskatchewan River Delta in Canada, from Landsat, SPOT and RapidEye images. Landsat results compared favourably with Canadian National Hydro Network (CNHN) GeoBase data, with deviations between SWCA classifications and the base CNHN GeoBase shapefile of ~2%. Difference levels between the extracted SWCA layer from Landsat and the higher resolution commercial satellites (SPOT and RapidEye) were also less than 2%. SWCA was tightly linked to discharge and level measurements from in-channel gauges (r² > 0.70). Using the SWCA versus discharge relationship for the gauge with the longest record, we show that peak summer SWCA has declined by half over the last century, from 13% of our study area to 6%, with likely implications for fish and wildlife production.