**5.2 Catchment areas of lakes**

Water authorities need tools to monitor and assess the status and the changes of basins so as to optimize and regulate their usage and to avoid depletion of the water resources. Up to date information about land cover, land use, vegetation status and their changes over time (e.g. seasonally) is important for the understanding and modelling of hydrological processes such as infiltration, runoff rates, evapotranspiration and water needs. Additional EOderived information such as land cover, DEMs (digital elevation models) or surface water variations can be used to infer properties of surface waters and aquifers, or used in water cycle models (e.g. to calculate evapotranspiration). In order to interpret these discrepancies the water basin status and the changes that are taking place need to be analyzed.

The collected information is reviewed and analyzed and the result of the compilation is shown in the form of various maps. Multi-temporal analysis of Landsat- 5 / 7, Enhanced Thematic Mapper Plus (ETM+) scenes, Envisat MERIS and one ASTER scene have been used in the analysis of the catchment areas. Special emphasis is given on the catchment delineation using DEMs available for the lake basins. The analysis included various types of DEMs like the SRTM (100 m resolution) and ASTER (30 m resolution) DEMs. Catchments of river networks are fundamental to the automation of flow-routing management in

Fig. 16, the quality of water in the lake Ohrid is the highest among all lakes. Then follows Macro Prespa, Micro Prespa and Vegoritis while Petron shows the worst water quality. This MERIS based relative classification of lakes coincides with the classification based on the

CHL Concentration August 2007 TSM August 2007

CHL concentration August 2009 TSM August 2009

the water basin status and the changes that are taking place need to be analyzed.

Water authorities need tools to monitor and assess the status and the changes of basins so as to optimize and regulate their usage and to avoid depletion of the water resources. Up to date information about land cover, land use, vegetation status and their changes over time (e.g. seasonally) is important for the understanding and modelling of hydrological processes such as infiltration, runoff rates, evapotranspiration and water needs. Additional EOderived information such as land cover, DEMs (digital elevation models) or surface water variations can be used to infer properties of surface waters and aquifers, or used in water cycle models (e.g. to calculate evapotranspiration). In order to interpret these discrepancies

The collected information is reviewed and analyzed and the result of the compilation is shown in the form of various maps. Multi-temporal analysis of Landsat- 5 / 7, Enhanced Thematic Mapper Plus (ETM+) scenes, Envisat MERIS and one ASTER scene have been used in the analysis of the catchment areas. Special emphasis is given on the catchment delineation using DEMs available for the lake basins. The analysis included various types of DEMs like the SRTM (100 m resolution) and ASTER (30 m resolution) DEMs. Catchments of river networks are fundamental to the automation of flow-routing management in

available in situ data observations.

Fig. 16. Chl concentration and tsm

**5.2 Catchment areas of lakes** 

distributed hydrologic models and for the morphometric evaluation of river network structure. The analysis of the DEM resulted to the delineation of the hydrographic network of the area of the transnational Prespa basin. The ASTER DEM has been used to delineate the changes of the relief of the Vegoritis lake basin.

Geology plays a role in the region as it allows the interconnections of adjacent river basins, which is the case of Prespa and Ohrid lakes. Ground waters cannot be observed directly by existing EO satellites, however, location, orientation and length of lineaments can be derived from EO and can be used as input for studies of fractured aquifers (e.g. location of sites for water harvesting). Available geologic maps have been scanned, geo referenced, digitized for the whole region within the context of the GIS system, Figure 3. The original maps have been of different scales and information content. A great variety of rocks with varying age and lithology constitute the catchment areas. Available information on location of springs has been also integrated in the GIS database.

Fig. 17. Impact of anthropogenic factors to the lakes of the study area.

Monitoring Lake Ecosystems Using Integrated Remote

Prespa & Vegoritis lakes, while Ohrid lake remains stable.

and water quality characteristics of the lakes.

**6. Discussion** 

**7. References** 

Sensing / Gis Techniques: An Assessment in the Region of West Macedonia, Greece 203

An advantage of using remote sensing is that data for large areas within a single image can be collected quickly and relatively inexpensively, while this can be repeated through selected time intervals. It is clear that in order to make regional assessments, one must develop a means to extrapolate from well-studied areas, as the site of our inter-comparison, to other lakes. Since the strength of satellite imagery for lake monitoring is the regional scale dimension, more than one location has to be taken for reference in order to learn how to separate crucial environmental parameters from all kinds of important interfering phenomena. Deterioration of water quantity and quality parameters is interpreted for Macro

Monitoring of the lake ecosystems is of paramount importance for the overall development of a region. Remote sensing provides valuable information concerning different hydrological parameters of interest to a lake assessment project. Monitoring is supported due to the multi-temporal character of the data. Temporal changes for the last 30 years can be analyzed with the use of satellite imagery. Processing techniques that have been applied include integrated image processing / GIS vector data techniques. Satellite data generate GIS database information required for hydrological studies and the application of models. Neural network algorithms are quite effective for the satellite data classification. Generated database can be used to assess changes that are taking place in the lakes and its surrounding environment. The areal extent of the lakes has been mapped accurately in all cases. Using the adopted methodology various parameters concerning the lakes and their basins can be extracted related to the description of catchments, surface area, water-level, hydrogeology

Water quality parameters of the lakes can be retrieved from remote sensing. Peristrophic movements (gyres) can be clearly identified in the time series images, both in the optical and thermal bands of the Landsat satellite system for the Macro Prespa lake. Understanding the naturally occurring mixing processes in the lake aids in determining the ultimate fate of pollutants, and supports the application of good management strategies and practice. The high spatial resolution of the satellite images allow the surface currents and general circulation in lakes to be accurately identified using the multi-temporal imagery. This can assist in monitoring the clarity and general water quality of lakes. ENVISAT MERIS satellite data have been used for the assessment of spatio-temporal variability of selected water quality parameters like dispersion of suspended solids and chlorophyll concentration. Deterioration of water quantity and quality parameters is interpreted for both Macro Prespa and Vegoritis lakes. It is indicated that satellite monitoring is a viable alternative for spatiotemporal monitoring purposes of lake ecosystems. However, technology alone is insufficient to resolve conflicts among competing water uses. A more useful approach is to have specialists to support decision makers by making available to them the use of data and techniques.

Bukata, R. P., Jerome J. H., & Burton J. E. (1988). Relationships among Secchi disk depth,

Chacon-Torres, A., Ross, L., Beveridge, M. & Watson, A., 1992. The application of SPOT

waters. Journal of Great Lakes Research, 14(3), 347-355.

Mexico. International Journal of Remote Sensing, 13(4): 587-603.

beam attenuation coefficient, and irradiance attenuation coefficient for Great Lakes

multispectral imagery for the assessment of water quality in Lake Patzcuaro,

Natural and anthropogenic processes take place in the basins of Prespa and Vegoritis lakes and these have an impact on the water resources of the basins. The catchments of the three lakes have been described by the GIS based analysis of "Corine Land Cover Classification" Figure 17-D. MERIS data has been used for Corine land cover map updating because of their improved temporal resolution. Burnt areas due to the 2007 forest fires are detected and mapped on the MERIS data.

Surface mining takes place in Vegoritis lake basin with negative impacts of mining on the water resources, both surface and groundwater, which occur at various stages of the life cycle of the mines and even after their closure: 1.From the mining process itself, 2. From dewatering activities which are undertaken to make mining possible. 3. During the flooding of workings after extraction has ceased 4. By discharge of untreated waters after flooding is complete.

Anthropogenic factors seem to play a key role on the deterioration of the water resources of the region. Integrated Earth Observation / GIS techniques help to monitor changes in lake basins and can cover specific water management requirements, Table 2, Figure 17.


Table 2. Selected natural / anthropogenic impacts on the water resources of lakes

An advantage of using remote sensing is that data for large areas within a single image can be collected quickly and relatively inexpensively, while this can be repeated through selected time intervals. It is clear that in order to make regional assessments, one must develop a means to extrapolate from well-studied areas, as the site of our inter-comparison, to other lakes. Since the strength of satellite imagery for lake monitoring is the regional scale dimension, more than one location has to be taken for reference in order to learn how to separate crucial environmental parameters from all kinds of important interfering phenomena. Deterioration of water quantity and quality parameters is interpreted for Macro Prespa & Vegoritis lakes, while Ohrid lake remains stable.
