Assessing the dynamics of El-Rayan lakes, Egypt, using remote sensing techniques

The present study provided an integrated scheme of utilizing digital elevation models (DEMs) along with five Landsat satellite images between 1973 and 2013 in order to delineate the extent and capacity of El-Rayan depression, Egypt, and to highlight temporal changes which occurred upon the two anthropogenic lakes formed from the discharge of agricultural drainage wastewater within the depression. The capacity of the valley as well as water volume was estimated from DEM data, and water surface area was estimated by applying mathematical indices compiled from spectral bands in satellite data. The modified normalized difference water index (MNDWI) was the algorithm operated in this study. Results showed that the area of the depression at the sea level approaches about 352 km², and the depression can store as much water as 6.45 billion m³. Water body of the two lakes has experienced reduction by seepage, evaporation, and shrinking to about 86 km² in July 2013. Most shrinking was encountered at the lower lake due to drifting sand and local cultivation.