Studying the Intra-Annual Variability in Surface Area and Volume of Salton Sea, California, Using Remote Sensing-Based Water Indices and GIS

摘要

The Salton Sea is one of the largest inland man-made water bodies in California and supports vital habitat for birds and wildlife. However, the lake has been in a critical situation in the past few years due to decreasing water levels, receding shorelines, and increasing salinity. In this study, we quantify and analyze the long-term changes in the surface area and volume of the Salton Sea utilizing remote sensing-based spectral water indices and GIS. Landsat TM images of every five years during the period of 1995-2015 were used. Normalized difference water index (NDWI) and modified normalized difference water index (MNDWI) were computed to delineate open water features. These spectral indexes were calculated, analyzed, and classified independently to extract the lake surface area for each year in GIS. The index threshold for water was adjusted using aerial imagery from Google Earth as reference. The index that provided clear demarcation of water-non water boundary was chosen from visual analysis at lake-river confluence. The Database for Hydrological Time Series of Inland Waters (DAHITI) was used for surface area validation. The lake surface maps were generated from all remote sensing images and overlaid to produce lake surface area change maps over the study period. The volume calculation utilized one-foot bathymetric contour data, water surface elevation, and water maps. The calculated area agreed well with the validation data set with the difference of less than 0.5%. The assessment of the area and volume over the study period demonstrated significant variations. The reduction of surface area by 7.5% and volume by 19% was observed. Volume of the lake showed the potential of significant reduction in comparison to area and elevation. The proposed method can be used for the regular assessment of Salton Sea's dynamics and can help planners for developing various mitigation, management, and restoration projects of the Salton Sea.