Using GIS for Monitoring Lacustrine Ecosystem: a Case Study of Laguna de Gallocanta, Spain

International audience; Current research presents study of the hydrological characteristics in the surroundings of the Laguna de Gallocanta (Spain) using remote sensing methods and combination of two GIS: ArcGIS and Idrisi GIS. The methodology includes following workflow: 1) selection of the multi-temporal Landsat images and creating color composites; 2) Masking and overlaying study area out of the whole image; 3) Calculation of the direction and length of stream flow in the lake basin; 4) assessment of possible risks of floods and stability of coastal slopes. The research has aim of hydrological assessment testing GIS tools for environmental monitoring. The images are presented by Landsat ETM+, MSS and TM scenes acquired on years 1976, 1987, 1992 and 2000, respectively, with a cloud cover of 0%. The images were georeferenced in ArcGIS and rectified to the Grid Coordinate System using available vector layers. The georeferenced rectified image was then re-projected to the UTM projection WGS84 datum. The combinations of various bands (channels 2-1-4, 5-4-7, and 2-4-7) were tested and visualized. Second step included processing DEM (Digital Elevation Model) Data acquired by the SRTM providing high quality elevation data. The pre-processing included mosaicing images and cutting out study area. The hydrologically conditioning the DEM was performed: the elevations are modified in order to model flow directions. Modelling flow direction and flow accumulation was performed on the conditioned DEM using ArcGIS. The next step included extracting hydrologic features such as stream directions, length and basin extents from a DEM. The pit removal tool was used to remove error pits from a DEM. Final step included calculations of the flow direction and flow length that demonstrate the direction of flow out of each cell. Finally, using Basin function all cells belonging to the watersheds of one or more target cells were calculated. The results shown that area has sensitive hydrological settings which explains its prone to the environmental change. The research demonstrated successful use of GIS for the purposes of hydrological modeling in the environmental studies.